A high-speed hair dryer under low-voltage direct-current power supply and a speed regulation method thereof

Abstract

The present application relates to hair dryer control technical field, specifically to a kind of high-speed hair dryer under low-voltage direct current power supply and its speed regulation method, the low-voltage direct current voltage is 24~48VDC, method includes: S1, the current signal of motor bus is collected, to sampling current is carried out direct current bias real-time compensation processing, obtains the three-phase stator current after compensation;S2, to the three-phase stator current is carried out stationary coordinate transformation and rotation coordinate transformation in turn, obtains excitation current component and torque current component under rotation coordinate system.The present application is based on sensorless magnetic field oriented control as the basic framework, for low-voltage direct current power supply scene optimization current sampling correction, rotor position estimation and modulation driving full-link strategy, improve the existing low-voltage hair dryer high-speed running position estimation deviation, commutation timing is not accurate, current ripple is too high.

Description

Technical Field

[0001] This invention relates to the field of hair dryer control technology, specifically to a high-speed hair dryer powered by low-voltage DC and its speed adjustment method. Background Technology

[0002] High-speed hair dryers rely on the strong airflow generated by a high-speed motor to quickly remove moisture from the hair, significantly shortening drying time compared to traditional low-speed hair dryers. Combined with temperature control and negative ion functions, they reduce the damage to hair caused by high temperatures. They are now widely used in homes, hotel rooms, and other settings. Most mainstream high-speed hair dryers use brushless motors as their power source, along with drive control circuits to achieve multiple speed and temperature settings.

[0003] Most high-speed hair dryers currently use a 220V AC power supply, which poses certain electrical safety hazards in high-humidity environments such as bathrooms: First, high-voltage power supply places high demands on product insulation design, material quality, and manufacturing processes; inferior or aging materials are prone to cracking, leading to leakage risks. Second, humid environments significantly increase the lethality of high-voltage electric shocks. Third, high power corresponds to high current; repeated bending of the power cord can easily cause overheating and short circuits, and more than half of electrical fires are related to power cord damage. Fourth, if the temperature control device of a high-power heating element malfunctions, the temperature can rapidly spiral out of control, leading to safety accidents.

[0004] Most existing hair dryer solutions powered by 24~48VDC low-voltage DC power supply use a simple square wave drive method to control the brushless motor. In the high speed range of more than 100,000 rpm, the rotor position estimation deviation will increase significantly, resulting in inaccurate motor commutation timing and increased current ripple. This will not only aggravate operating noise and energy loss, but also make it difficult to maintain stable high speed output under low voltage conditions. Even with the introduction of a general sensorless FOC control framework, unique technical challenges remain in low-voltage DC power supply scenarios: First, the bus current amplitude is relatively small under low-voltage conditions, significantly increasing the proportion of DC bias error in the sampling circuit. Conventional single-calibration schemes cannot cover bias drift throughout the entire operating cycle, resulting in insufficient current control accuracy under low-current conditions. Second, the low-voltage bus voltage amplitude is limited, leading to low voltage utilization under conventional linear SVPWM modulation, making it difficult to support continuous high-speed output. Third, the back EMF amplitude is relatively low under low-voltage high-speed conditions, making traditional fixed-gain sliding mode observers unable to balance low-speed chatter suppression and high-speed convergence performance, resulting in a sharp increase in position estimation deviation as speed increases. Fourth, switching losses account for a higher proportion of total losses under low-voltage power supply, and fixed carrier frequency schemes cannot balance current ripple and switching losses across the entire speed range, resulting in low overall operating efficiency. Existing solutions cannot simultaneously meet the electrical safety requirements of high-humidity scenarios and the performance demands of high-speed dry-generating power. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-speed hair dryer powered by low-voltage DC and its speed control method, which solves the problems of large position estimation deviation, inaccurate commutation, and high losses in existing low-voltage DC powered hair dryers at high speeds, making it difficult to maintain stable high-speed output and failing to balance electrical safety and hair drying performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a speed control method for a high-speed hair dryer powered by low-voltage DC, wherein the low-voltage DC voltage is 24~48VDC, and the method includes: S1. Acquire the current signal of the motor bus, and obtain the DC bias compensation amount by combining initial static calibration and dynamic zero vector update during operation. Perform real-time DC bias compensation processing on the sampled current to obtain the compensated three-phase stator current. S2. Perform static coordinate transformation and rotating coordinate transformation on the three-phase stator current in sequence. Based on the rotor position angle and estimated speed of the previous control cycle, perform linear interpolation to predict the rotor position angle of the current cycle. Perform rotating coordinate transformation with the predicted rotor position angle to obtain the excitation current component and torque current component in the rotating coordinate system. S3. A sliding mode observer with gain adaptively adjusted with motor speed is used to estimate the back EMF of the motor. The estimated back EMF is low-pass filtered and the filter phase delay is compensated in real time according to the current speed. The rotor position angle and the estimated motor speed are output through phase-locked loop calculation. S4. Dynamically adjust the PWM carrier frequency according to the current operating speed of the motor, combine the target voltage vector to perform SVPWM modulation, configure the overmodulation control strategy to compress the zero vector action time and expand the modulation range, and generate three-phase bridge arm drive signals. S5. Based on the target speed and the estimated speed of the motor, a speed closed loop is constructed. Combined with the excitation current component and the torque current component, a current double closed loop is constructed, and the output control quantity drives the high-speed brushless motor to operate.

[0007] Furthermore, step S1 specifically includes: During the idle phase before motor startup, the current sampling value under the three-phase bridge arm fully off state is collected and stored in the register as the initial bias voltage; During motor operation, the sampling current at the zero vector action moment is calculated by moving average at fixed intervals, and the bias compensation value is dynamically updated. The sampled current is corrected by using the real-time updated bias compensation value to obtain the compensated three-phase stator current.

[0008] Furthermore, step S2 specifically includes: Perform Clarke transformation on the compensated three-phase stator current to obtain the current components in the two-phase stationary coordinate system; Based on the rotor position angle and estimated speed of the previous control cycle, the rotor position angle of the current cycle is predicted by linear interpolation; Using the predicted rotor position angle as input, the Park transformation is performed on the current components in the two-phase stationary coordinate system to obtain the excitation current component and torque current component in the rotating coordinate system.

[0009] Furthermore, step S3 specifically includes: Using the stator voltage setpoint and current sampling value in the stationary coordinate system as input, a sliding mode observer is constructed, and the sliding mode gain of the sliding observer is adaptively adjusted with the motor speed. The back electromotive force estimate output by the sliding mode observer is subjected to low-pass filtering, and the phase delay caused by the filtering is compensated in real time according to the current rotational speed. The back EMF estimate after phase compensation is input into the phase-locked loop, and the rotor position angle and the estimated motor speed are output through closed-loop regulation.

[0010] Furthermore, step S4 specifically includes: The current operating speed of the motor is detected, and the PWM carrier frequency is reduced accordingly as the speed increases. The sector where the target voltage vector is located is determined by the positive or negative sign of the characteristic variables, and the action time of each vector is calculated based on the volt-second balance principle; When the magnitude of the target voltage vector exceeds the linear modulation range, overmodulation control is performed to compress the zero vector action time.

[0011] Furthermore, the method also includes a three-stage smooth start-up process: During the rotor pre-positioning stage, a gradually increasing DC current is supplied to the two-phase windings of the motor to drag the rotor to the preset initial position. During the open-loop acceleration phase, the V / F control mode is used to increase the frequency and amplitude of the output voltage according to a preset slope, thereby driving the motor to accelerate synchronously. During the closed-loop switching phase, when the difference between the open-loop given speed and the observer estimated speed meets the preset conditions, the system switches to sensorless FOC closed-loop control through a weighted gradual change method.

[0012] Furthermore, the method also includes an adaptive adjustment step for the commutation advance angle: The current motor speed and bus current are collected in real time. The basic value of the commutation advance angle is obtained based on the speed query, and the basic value of the commutation advance angle is dynamically corrected according to the bus current. Adjust the motor commutation timing based on the corrected commutation advance angle.

[0013] Furthermore, the method also includes a temperature-controlled speed adjustment step: Collect the air temperature data from the air outlet of the blower, and obtain the real-time air temperature value after filtering; In warm air mode, a dual closed-loop temperature control structure with an outer temperature loop and an inner power loop is constructed, and a power control signal for the heating wire is output. When the outlet temperature exceeds the safety threshold, the heating wire power is reduced and the target motor speed is increased simultaneously. Once the temperature returns to the normal range, the original operating parameters are restored.

[0014] Furthermore, the method also includes multiple fault-tolerant protection steps: Real-time monitoring of bus current, motor speed and bus voltage triggers overcurrent protection, locked rotor protection and over / under voltage protection respectively; Real-time temperature data of motor windings and main control board is collected, and the motor speed and heat generation power are reduced in stages when the temperature exceeds the standard. All protection measures employ a tiered processing logic, prioritizing the elimination of abnormal states through derating.

[0015] The present invention also provides a high-speed hair dryer powered by low-voltage DC, wherein the low-voltage DC voltage is 24~48VDC, and the hair dryer includes: The low-voltage DC input module is used to connect to a low-voltage DC power supply. It has a built-in interface switch and reverse connection protection circuit to realize on-off control and reverse connection protection. The power conversion module is connected to the low-voltage DC input module and has a built-in DC-DC conversion circuit for converting the input DC voltage into multiple working voltages such as 12V and outputting them. The main control unit, connected to the power conversion module, uses an MCU microcontroller main control chip to run the speed control algorithm and output multiple control signals. The three-phase motor drive module is connected to the low-voltage DC input module and the main control unit respectively, and is used to receive the PWM signal output by the main control unit to drive the 48V three-phase high-speed brushless motor to run. A temperature control sampling module, connected to the main control unit, uses an NTC temperature control circuit to collect air outlet temperature data and transmit it to the main control unit; The heating wire control module is connected to the low-voltage DC input module and the main control unit respectively, and is adapted to 24~48VDC bus voltage input. It is used to receive the control signal from the main control unit and adjust the heating power of the heating wire assembly. A negative ion generating module, connected to the main control unit, is used to receive start / stop control signals from the main control unit and release high-concentration negative ions; The human-computer interaction module, connected to the main control unit, includes a temperature button and a status indicator unit, used to receive user operation commands and display the operating status.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, based on a sensorless magnetic field-oriented control framework, addresses the unique technical challenges of 24-48VDC low-voltage DC power supply scenarios. It optimizes the entire power supply chain—from current sampling correction and rotor position estimation to modulation drive—to improve existing low-voltage blowers that suffer from large position estimation errors, inaccurate commutation timing, and high current ripple during high-speed operation. The current sampling stage introduces an initial calibration superimposed with a dynamically updated DC bias compensation mechanism. Before startup, the inherent bias of the sampling circuit is calibrated, and during operation, zero-vector sampling points are used to dynamically correct operating condition drift errors. This specifically addresses the high proportion of bias errors and current control distortion under low-voltage, low-current conditions, improving current control accuracy in these scenarios. The rotor position estimation employs an adaptive gain sliding mode observer combined with phase compensation and a phase-locked loop structure. The sliding mode gain is adjusted in real-time with the rotational speed to adapt to the low back EMF amplitude characteristic under low voltage conditions. This balances low-speed stability with high-speed convergence performance, maintaining a small position estimation error even at high speeds, ensuring accurate commutation timing, and reducing commutation losses and torque ripple. The modulation drive side dynamically adjusts the carrier frequency according to the speed, introduces space vector pulse width modulation and overmodulation control to balance the problem of high switching loss ratio under low voltage, and improves DC voltage utilization. With the help of adaptive correction of commutation advance angle to optimize high-speed output efficiency, the motor can stably maintain high speed continuous output under 24~48VDC low voltage power supply conditions, reduce operating noise and heat loss, and adapt to the electrical safety characteristics of low voltage DC power supply to meet the high-speed drying performance requirements in high humidity application scenarios. Attached Figure Description

[0017] Figure 1 This is an overall flowchart of the high-speed hair dryer speed adjustment method of the present invention; Figure 2 This is a module architecture diagram of the low-voltage DC high-speed hair dryer of the present invention; Figure 3 This is a schematic diagram of the hardware structure of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some 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.

[0019] Please see Figure 1 This invention provides a speed control method for a high-speed hair dryer powered by low-voltage DC, wherein the low-voltage DC voltage is 24~48VDC, and the method includes: S1. Acquire the current signal of the motor bus, and obtain the DC bias compensation amount by combining initial static calibration and dynamic zero vector update during operation. Perform real-time DC bias compensation processing on the sampled current to obtain the compensated three-phase stator current. S2. Perform static coordinate transformation and rotating coordinate transformation on the three-phase stator current in sequence. Based on the rotor position angle and estimated speed of the previous control cycle, perform linear interpolation to predict the rotor position angle of the current cycle. Perform rotating coordinate transformation with the predicted rotor position angle to obtain the excitation current component and torque current component in the rotating coordinate system. S3. A sliding mode observer with gain adaptively adjusted with motor speed is used to estimate the back EMF of the motor. The estimated back EMF is low-pass filtered and the filter phase delay is compensated in real time according to the current speed. The rotor position angle and the estimated motor speed are output through phase-locked loop calculation. S4. Dynamically adjust the PWM carrier frequency according to the current operating speed of the motor, combine the target voltage vector to perform SVPWM modulation, configure the overmodulation control strategy to compress the zero vector action time and expand the modulation range, and generate three-phase bridge arm drive signals. S5. Based on the target speed and the estimated speed of the motor, a speed closed loop is constructed. Combined with the excitation current component and the torque current component, a current double closed loop is constructed, and the output control quantity drives the high-speed brushless motor to operate.

[0020] Specifically, this embodiment's speed control process is based on sensorless field-oriented control, and it optimizes the entire chain to address the unique problems of large small-current sampling errors, high-speed position estimation deviations, insufficient voltage utilization, and high switching losses in 24~48VDC low-voltage DC power supply scenarios. The current signal is acquired from the motor bus sampling circuit, corrected by bias compensation, and then enters the coordinate transformation stage to convert the three-phase stationary quantity into a rotating DC quantity. The converted current component is fed into the current closed-loop regulator and also fed into the sliding mode observer for rotor position estimation. The speed and position signals output by the observer are fed back to the coordinate transformation stage for angle calculation and also fed into the speed closed loop to form the outer loop regulation. The speed loop outputs a torque current setpoint, which is compared with the current sampling value and then outputs a target voltage vector through the regulator. This target voltage vector is then modulated by SVPWM to generate a drive signal that acts on the three-phase bridge arms. A dynamic carrier frequency adjustment mechanism switches the switching frequency in real time according to the speed, balancing current ripple and switching losses at different speeds. The entire control process is completed within a single main control chip, with each stage executed sequentially according to a fixed control cycle, and data updated and transmitted periodically. This eliminates current errors caused by sampling bias, improves rotor position estimation accuracy in high-speed ranges, optimizes switching loss distribution, and ensures stable control of speed and current through a three-stage closed-loop structure. It can achieve continuous and stable output of over 100,000 RPM under low-voltage DC power supply conditions, reduce motor operating noise and heat loss, and take into account both electrical safety and dry-running performance requirements.

[0021] In a specific embodiment, step S1 specifically includes: During the idle phase before motor startup, the current sampling value under the three-phase bridge arm fully off state is collected and stored in the register as the initial bias voltage; During motor operation, the sampling current at the zero vector action moment is calculated by moving average at fixed intervals, and the bias compensation value is dynamically updated. The sampled current is corrected by using the real-time updated bias compensation value to obtain the compensated three-phase stator current.

[0022] Specifically, DC bias compensation employs an initial calibration superimposed with dynamic updates, covering bias error correction throughout the entire operating cycle of the equipment and adapting to the significant impact of bias errors under low-voltage, low-current conditions. Current sampling is achieved through a precision sampling resistor connected in series with the bus. The sampled voltage is conditioned by an operational amplifier and input to the analog-to-digital converter port of the main control chip, converting it into a digital quantity for subsequent calculations. When the bridge arm is fully off before motor startup, no current flows through the windings. The sampled value at this time is the inherent bias of the sampling circuit. After multiple consecutive samplings, the average value is stored in a register as the initial compensation value, which can quickly eliminate inherent system deviations. During motor operation, at the zero-vector action moment, the three-phase windings are in a short-circuited state, and the ideal value of the stator current is zero. The sampling deviation at this time can reflect the real-time bias error under the current operating conditions. The analog-to-digital conversion sampling trigger point is set at the zero-vector action midpoint of each PWM cycle, avoiding switching spike interference and improving sampling accuracy. The fixed interval for bias updates can be set according to the control cycle, for example, performing a bias update once every 16 control cycles, balancing the update rate and computational load. Moving average calculation can filter out random fluctuations caused by sampling noise. The window length can be adjusted according to the sampling noise level, and is usually set to 8 sampling times. The real-time corrected three-phase stator current can accurately reflect the true current state of the winding, avoid current control deviation caused by bias error, and reduce torque ripple and current ripple. It can significantly improve control accuracy, especially under low voltage and low current conditions.

[0023] In one specific embodiment, step S2 specifically includes: Perform Clarke transformation on the compensated three-phase stator current to obtain the current components in the two-phase stationary coordinate system; Based on the rotor position angle and estimated speed of the previous control cycle, the rotor position angle of the current cycle is predicted by linear interpolation; Using the predicted rotor position angle as input, the Park transformation is performed on the current components in the two-phase stationary coordinate system to obtain the excitation current component and torque current component in the rotating coordinate system.

[0024] Specifically, coordinate transformation includes two steps: static coordinate transformation and rotating coordinate transformation. The Clarke transformation, derived from the constraint that the sum of the instantaneous values ​​of the three-phase currents in a three-phase three-wire system is zero, can reduce the three-phase currents to two orthogonal currents, reducing subsequent calculations and improving the execution efficiency of the control cycle. The transformation formula is as follows:

[0025] In the formula, , The two-phase stator current sampling values ​​after compensation. The α-axis stationary current component This represents the β-axis static current component.

[0026] Rotor position prediction is used to offset the control delay caused by sampling, calculation, and drive output, avoiding control deviations caused by position angle lag. In low-voltage, high-speed conditions, it can effectively reduce the impact of control delay on current control accuracy. Linear interpolation prediction calculates the position angle of the current cycle based on the rotor position angle and estimated speed from the previous control cycle. The calculation method is to add the position angle of the previous cycle and the estimated speed multiplied by the control cycle duration, achieving delay compensation without complex calculations.

[0027] The Park transformation, based on the principle of coordinate rotation projection, projects the current components from the two-phase stationary coordinate system onto a coordinate system that rotates synchronously with the rotor, obtaining the DC current for convenient closed-loop regulation. This transformation uses the predicted rotor position angle as the reference angle, and the transformation formula is as follows:

[0028] In the formula, Predict the rotor position angle for the current cycle. This is the excitation current component. This represents the torque current component.

[0029] The Clarke transform and Park transform are progressively related. First, the three-phase to two-phase stationary coordinates are reduced, then the stationary to rotating coordinates are transformed, ultimately decoupling the excitation and torque components. In actual operation, if the sampled phase a current is 2A and the phase b current is -1A at a certain moment, the Clarke transform can calculate the α-axis current as 2A and the β-axis current as 0A. If the predicted rotor position angle is 30°, the Park transform can calculate the d-axis current as approximately 1.732A and the q-axis current as approximately -1A. The transformed DC currents can be controlled without steady-state error using a PI controller, adjusting the motor's excitation and torque outputs separately to improve control performance.

[0030] In one specific embodiment, step S3 specifically includes: Using the stator voltage setpoint and current sample value in the stationary coordinate system as input, a sliding mode observer is constructed, and the sliding mode gain of the sliding mode observer is adaptively adjusted with the motor speed. The back electromotive force estimate output by the sliding mode observer is low-pass filtered, and the phase delay caused by the filtering is compensated in real time according to the current rotational speed. The back EMF estimate after phase compensation is input into the phase-locked loop, and the rotor position angle and the estimated motor speed are output through closed-loop regulation.

[0031] Specifically, the sliding mode observer is constructed based on the motor stator voltage equation. It estimates the stator-side back electromotive force (EMF) using a sliding mode control law, and then extracts the rotor position information. Conventional fixed-gain sliding mode observers struggle to balance low-speed chatter suppression with high-speed convergence performance; therefore, a gain-adaptive adjustment scheme is adopted. At high speeds, the back EMF amplitude increases, requiring a larger gain to ensure rapid observer convergence; at low speeds, the back EMF amplitude is lower, and reducing the gain can suppress sliding mode chatter and improve operational stability. The adaptive sliding mode gain is calculated as follows:

[0032] In the formula, For real-time sliding mode gain, Based on the gain, This is the speed proportional coefficient. Estimate the electrical angular velocity of the motor.

[0033] The base gain and proportional coefficient can be determined through bench testing. During the testing process, the parameters are gradually adjusted, and the degree of current chattering during low-speed operation and the position estimation error during high-speed operation are observed. The parameter combination with stable convergence and small error across the entire speed range is selected as the final calibration value. For example, if the base gain is set to 15 and the proportional coefficient is set to 0.008, when the estimated electric angular velocity of the motor is 1000 rad / s, the real-time sliding mode gain is 23, which can suppress low-speed chattering while ensuring the observation convergence speed.

[0034] The back EMF signal output by the sliding mode observer contains switching ripple and chattering components, requiring first-order low-pass filtering to extract a smooth back EMF signal. Low-pass filtering introduces phase delay, which increases with the input signal frequency. At low voltage and high speeds, the high electrical frequency amplifies the impact of phase delay on position estimation accuracy. Therefore, the delay angle needs to be calculated in real-time based on the electrical frequency corresponding to the current rotational speed and superimposed on the output position angle to achieve phase compensation, avoiding phase deviations in position estimation. The phase-compensated back EMF signal is input to a phase-locked loop (PLL), which tracks the phase of the back EMF through closed-loop regulation, outputting smooth rotor position angle and rotational speed signals. The PLL bandwidth can be adapted to the operating speed conditions; reducing bandwidth at low speeds improves filtering effectiveness, while increasing bandwidth at high speeds ensures dynamic response.

[0035] The four stages—sliding mode observation, low-pass filtering, phase compensation, and phase-locked loop—are sequentially connected, with the output of each stage serving as the input for the next, ultimately yielding stable and accurate rotor position and speed signals. This observation scheme maintains a small position estimation error in the high-speed range above 100,000 RPM, ensuring accurate commutation timing and reducing commutation losses and torque ripple.

[0036] In one specific embodiment, step S4 specifically includes: The current operating speed of the motor is detected, and the PWM carrier frequency is reduced accordingly as the speed increases. The sector where the target voltage vector is located is determined by the positive or negative sign of the characteristic variables, and the action time of each vector is calculated based on the volt-second balance principle; When the magnitude of the target voltage vector exceeds the linear modulation range, overmodulation control is performed to compress the zero vector action time.

[0037] Specifically, dynamic carrier frequency adjustment can balance current ripple and switching losses. Switching losses account for a higher proportion of total losses under low-voltage power supply. Dynamic adjustment can effectively optimize operating efficiency across the entire speed range. A higher carrier frequency is used at low speeds to reduce current ripple and operating noise, while the carrier frequency is lowered at high speeds to reduce the number of switching operations on power devices, thereby reducing switching losses and improving energy utilization efficiency under low-voltage power supply. The relationship between carrier frequency and speed can be calibrated through loss testing. The overall operating efficiency at multiple carrier frequencies is tested at different speed points, and the corresponding value with the best efficiency is stored in a lookup table. During operation, the corresponding carrier frequency can be directly obtained from the table based on the current speed. For example, the carrier frequency is set to 20kHz when the speed is below 30,000 RPM, and lowered to 12kHz when the speed is above 100,000 RPM, with a smooth linear transition in the intermediate speed range.

[0038] Space vector pulse width modulation (SVM) is based on the volt-second balance principle. It decomposes the target voltage vector into a combination of adjacent basic vectors and a zero vector. By combining the positive and negative values ​​of three characteristic variables, the sector in which the voltage vector resides can be quickly determined, reducing the computational burden of sector identification. The duration of each vector is calculated according to the volt-second balance principle, ensuring that the average output voltage within one switching cycle matches the target voltage. When the target voltage vector amplitude exceeds the linear modulation range corresponding to the inscribed circle of the hexagon, the modulation range is expanded by gradually compressing the zero vector duration, improving DC bus voltage utilization and overcoming the low-voltage bus amplitude limitation to achieve higher speed output. The overmodulation process employs a smooth transition strategy, gradually compressing the zero vector time as the voltage amplitude increases to avoid current surges and speed fluctuations caused by modulation mode switching.

[0039] In one specific embodiment, the method further includes a three-stage smooth startup step: During the rotor pre-positioning stage, a gradually increasing DC current is supplied to the two-phase windings of the motor to drag the rotor to the preset initial position. During the open-loop acceleration phase, the V / F control mode is used to increase the frequency and amplitude of the output voltage according to a preset slope, thereby driving the motor to accelerate synchronously. During the closed-loop switching phase, when the difference between the open-loop given speed and the observer estimated speed meets the preset conditions, the system switches to sensorless FOC closed-loop control through a weighted gradual change method.

[0040] Specifically, the three-stage starting scheme solves the problem of unknown initial position in sensorless motors, ensuring a smooth and reliable starting process, avoiding start-up step loss and overcurrent impact, and adapting to the characteristic of small overcurrent tolerance margin under low-voltage power supply. In the rotor pre-positioning stage, a slowly increasing DC current is applied to two designated phase windings, generating a stator magnetic field in a fixed direction, dragging the rotor to the preset position, providing an initial position reference for subsequent open-loop operation. The current ramp-up slope can be adjusted according to the motor load inertia to avoid rotor oscillation caused by excessively rapid current rise; it is typically set to ramp up to the target current within several hundred milliseconds.

[0041] During the open-loop acceleration phase, a constant voltage-to-frequency ratio control method is employed, synchronously increasing the frequency and amplitude of the output voltage to drive the motor to accelerate in sync with the magnetic field. The voltage-to-frequency ratio parameter can be determined based on the motor's rated voltage and rated speed, ensuring stable motor flux during acceleration and preventing over-excitation or under-excitation issues. The acceleration slope can be adjusted according to starting performance requirements, balancing starting speed and operational smoothness.

[0042] When the deviation between the open-loop given speed and the observer's estimated speed remains below a preset threshold, the observer is deemed to have achieved stable convergence, and the system enters the closed-loop switching phase. The preset threshold can be set as a certain percentage of the rated speed, such as 15% of the rated speed. The switching process employs a weighted gradual strategy, progressively increasing the weight of the closed-loop control variable and decreasing the weight of the open-loop control variable within a set switching duration, ultimately switching completely to sensorless FOC closed-loop control. The switching duration can be set to several hundred milliseconds to ensure a smooth transition in speed and current without significant impact during the switching process.

[0043] In one specific embodiment, the method further includes a commutation advance angle adaptive adjustment step: The current motor speed and bus current are collected in real time. The basic value of the commutation advance angle is obtained based on the speed query, and the basic value of the commutation advance angle is dynamically corrected according to the bus current. Adjust the motor commutation timing based on the corrected commutation advance angle.

[0044] Specifically, commutation advance angle adjustment is used to compensate for the current phase delay caused by winding inductance during high-speed operation, ensuring that the current is in the optimal phase at the commutation moment, thereby improving the motor's torque output capability and operating efficiency. The optimal commutation advance angle base value at different speeds can be obtained through bench calibration. By gradually adjusting the advance angle value at a fixed speed and recording the corresponding motor efficiency and torque output, the value with the highest efficiency is selected as the base value of the advance angle at that speed. Multiple sets of speed-corresponding values ​​are stored in a lookup table, and the base value can be directly obtained from the table based on the current speed during operation.

[0045] The bus current reflects the motor's load condition. As the load increases, the bus current rises, and the winding voltage drop and current phase change accordingly. Therefore, a current correction term needs to be introduced to adjust the base value of the advance angle. The correction calculation method is as follows:

[0046] In the formula, This is the corrected commutation advance angle. This is the base value of the advance angle at the corresponding speed. This is the current correction factor. This represents the real-time bus current.

[0047] The current correction factor can be determined through calibration. By varying the load at a fixed speed and recording the optimal commutation advance angle for different bus currents, the correction factor value can be obtained through fitting. For example, if the base advance angle at a certain speed is 12° electrical angle and the current correction factor is set to 0.5° / A, when the bus current is 4A, the corrected commutation advance angle is 14°, which can offset the phase lag caused by increased load and ensure optimal commutation timing. By adaptively adjusting the commutation advance angle, commutation timing can be optimized across the entire speed and load range, reducing commutation losses, improving the motor's output capability at high speeds, and adapting to the performance requirements of low-voltage power supply scenarios.

[0048] In one specific embodiment, the method further includes a temperature-controlled speed adjustment step: Collect the air temperature data from the air outlet of the blower, and obtain the real-time air temperature value after filtering; In warm air mode, a dual closed-loop temperature control structure with an outer temperature loop and an inner power loop is constructed, and a power control signal for the heating wire is output. When the outlet temperature exceeds the safety threshold, the heating wire power is reduced and the target motor speed is increased simultaneously. Once the temperature returns to the normal range, the original operating parameters are restored.

[0049] Specifically, the air outlet temperature is sampled using a negative temperature coefficient thermistor. The sampled signal is then processed by a first-order low-pass filter to obtain a smooth real-time air temperature value, filtering out sampling noise caused by airflow fluctuations and improving the stability of temperature detection. In heating mode, a dual closed-loop temperature control structure is employed. The outer temperature loop outputs a power setpoint based on the deviation between the set air temperature and the real-time air temperature, while the inner power loop outputs a control signal based on the deviation between the power setpoint and the real-time heating power, adjusting the duty cycle of the heating element to achieve precise and stable air temperature control. This dual closed-loop structure improves temperature response speed while ensuring steady-state control accuracy, preventing large fluctuations in air temperature.

[0050] When the outlet temperature exceeds the safety threshold, the temperature control linkage protection is triggered. This reduces the output power of the heating element to decrease heat generation and simultaneously increases the target motor speed to increase airflow and accelerate heat dissipation, causing the outlet temperature to quickly drop back to a safe range. The safety threshold can be set according to product safety specifications, and the recovery threshold can be set below the safety threshold, creating a hysteresis loop to prevent frequent activation and deactivation of the protection mechanism. Once the temperature returns to the normal range, the heating element power and motor speed are gradually restored to their original settings, ensuring a good user experience while preventing high-temperature damage to hair and improving safety.

[0051] In one specific embodiment, the method further includes multiple fault-tolerant protection steps: Real-time monitoring of bus current, motor speed and bus voltage triggers overcurrent protection, locked rotor protection and over / under voltage protection respectively; Real-time temperature data of motor windings and main control board is collected, and the motor speed and heat generation power are reduced in stages when the temperature exceeds the standard. All protection measures employ a tiered processing logic, prioritizing the elimination of abnormal states through derating.

[0052] Specifically, multiple fault-tolerant protections cover various abnormal operating conditions, including electrical, mechanical, and temperature-related factors, ensuring safe equipment operation, extending service life, and adapting to the device tolerance characteristics of low-voltage power supply systems. Bus current monitoring enables overcurrent protection, with thresholds set according to the current tolerance capabilities of power devices and motors, divided into a primary derating threshold and a secondary shutdown threshold. When the current exceeds the primary threshold, the motor torque output is reduced to limit the current; when the current exceeds the secondary threshold, the drive output is directly shut off to prevent damage to power devices and motors. Motor speed monitoring combined with current detection enables stall protection. When the speed remains below the set threshold and the bus current is high, a stall state is identified, and derating or shutdown operations are executed to prevent motor overheating and burnout. Bus voltage monitoring enables over / undervoltage protection. The normal voltage range is set according to the power supply specifications; when the voltage exceeds the normal range, corresponding protection is triggered to prevent device damage due to abnormal voltage.

[0053] Temperature sampling of the motor windings and main control board enables overheat protection. Temperature thresholds are set according to the temperature resistance rating of the components, and are also divided into two levels. When the temperature reaches the first-level threshold, the motor speed and power output are reduced in stages to decrease heat generation. When the temperature reaches the second-level threshold, a shutdown operation is performed, waiting for the temperature to drop. All protections employ a tiered processing strategy, prioritizing derating to eliminate abnormal states without direct shutdown, minimizing the impact on user experience. Shutdown protection is only implemented when abnormal states cannot be eliminated through derating, balancing equipment safety and operational continuity.

[0054] Please see Figures 2-3 The present invention also provides a high-speed hair dryer powered by low-voltage DC power, comprising: The low-voltage DC voltage is 24~48VDC, and the hair dryer includes: The low-voltage DC input module is used to connect to a low-voltage DC power supply. It has a built-in interface switch and reverse connection protection circuit to realize on-off control and reverse connection protection. The power conversion module is connected to the low-voltage DC input module and has a built-in DC-DC conversion circuit for converting the input DC voltage into multiple working voltages such as 12V and outputting them. The main control unit, connected to the power conversion module, uses an MCU microcontroller main control chip to run the speed control algorithm and output multiple control signals. The three-phase motor drive module is connected to the low-voltage DC input module and the main control unit respectively, and is used to receive the PWM signal output by the main control unit to drive the 48V three-phase high-speed brushless motor to run. A temperature control sampling module, connected to the main control unit, uses an NTC temperature control circuit to collect air outlet temperature data and transmit it to the main control unit; The heating wire control module is connected to the low-voltage DC input module and the main control unit respectively, and is adapted to 24~48VDC bus voltage input. It is used to receive the control signal from the main control unit and adjust the heating power of the heating wire assembly. A negative ion generating module, connected to the main control unit, is used to receive start / stop control signals from the main control unit and release high-concentration negative ions; The human-computer interaction module, connected to the main control unit, includes a temperature button and a status indicator unit, used to receive user operation commands and display the operating status.

[0055] Specifically, the low-voltage DC input module connects to an external 24~48VDC low-voltage DC power supply. A built-in interface switch controls the power supply to the entire unit, and a reverse connection protection circuit prevents damage to downstream components from reversed polarity. The power conversion module includes a DC-DC converter circuit, converting the input DC voltage to a 12V operating voltage to power the main control chip, drive circuit, sampling circuit, and other units. The main control unit uses an MCU microcontroller chip as the control center, with built-in memory and a processing unit. It can run the aforementioned speed control algorithm and protection logic, and output various control signals. Specifically, pin PA13 is used to detect the button input level; pin PA12 outputs a PWM signal to control the heating wire power; pin PA7 acquires the NTC temperature signal; pins PA5 and PA6 are used for current sampling to achieve overcurrent and stall protection; pin PA3 detects the input voltage to achieve over / undervoltage protection; and pins PA31, PA30, and PA32 are used for motor inductance detection to control motor commutation. The three-phase motor drive module includes a three-phase power bridge and drive circuit. It amplifies the PWM signal output from the main control unit and drives the power transistors to switch on and off, controlling the energization of the motor windings and driving a 48V three-phase high-speed brushless motor. The motor's maximum no-load speed can reach 110,000 rpm, and the air velocity at 2cm from the outlet is greater than 20m / s. The temperature control sampling module uses an NTC thermistor to build a temperature control circuit, collecting the temperature signal from the air outlet and transmitting it to the main control unit. This enables real-time temperature monitoring 100 times per second, preventing high-temperature damage to hair. The heating wire control module includes a power switch device. Based on the PWM control signal output from the main control unit, it adjusts the duty cycle of the heating wire assembly to regulate the heating power. The heating wire resistance is 3~5Ω, supporting both cool and warm air temperature modes. The negative ion generator module produces high-voltage ionized air, releasing 200 million high-concentration negative ions to deeply nourish hair and smooth frizz. The human-machine interface module includes temperature buttons and status indicator lights. It receives user commands for fan speed and temperature settings and displays the current operating status via the indicator unit. It supports two-speed fan adjustment. All modules work collaboratively according to power and signal flow to jointly control the speed, temperature, and auxiliary functions of the blower. The overall design complies with relevant national standards such as GB4706.1 and GB4706.15.

[0056] In summary, this invention, based on a sensorless magnetic field-oriented control framework, addresses the unique technical challenges of 24-48VDC low-voltage DC power supply scenarios. It optimizes the entire power supply chain—from current sampling correction and rotor position estimation to modulation drive—to improve existing low-voltage blowers that suffer from large position estimation errors, inaccurate commutation timing, and high current ripple during high-speed operation. The current sampling stage introduces an initial calibration superimposed with a dynamically updated DC bias compensation mechanism. Before startup, the inherent bias of the sampling circuit is calibrated, and during operation, zero-vector sampling points are used to dynamically correct operating condition drift errors. This specifically addresses the high proportion of bias errors and current control distortion under low-voltage, low-current conditions, improving current control accuracy in these scenarios. The rotor position estimation employs an adaptive gain sliding mode observer combined with phase compensation and a phase-locked loop structure. The sliding mode gain is adjusted in real-time with the rotational speed, adapting to the low back EMF amplitude characteristic under low voltage conditions. This balances low-speed stability with high-speed convergence performance, maintaining a small position estimation error even at high speeds, ensuring accurate commutation timing, and reducing commutation losses and torque ripple. The modulation drive side dynamically adjusts the carrier frequency according to the speed, introduces space vector pulse width modulation and overmodulation control to balance the problem of high switching loss ratio under low voltage, and improves DC voltage utilization. With the help of adaptive correction of commutation advance angle to optimize high-speed output efficiency, the motor can stably maintain high speed continuous output under 24~48VDC low voltage power supply conditions, reduce operating noise and heat loss, and adapt to the electrical safety characteristics of low voltage DC power supply to meet the high-speed drying performance requirements in high humidity application scenarios.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A speed control method for a high-speed hair dryer powered by low-voltage DC power, characterized in that, The low-voltage DC voltage is 24~48VDC, and the method includes: S1. Acquire the current signal of the motor bus, and obtain the DC bias compensation amount by combining initial static calibration and dynamic zero vector update during operation. Perform real-time DC bias compensation processing on the sampled current to obtain the compensated three-phase stator current. S2. Perform static coordinate transformation and rotating coordinate transformation on the three-phase stator current in sequence. Based on the rotor position angle and estimated speed of the previous control cycle, perform linear interpolation to predict the rotor position angle of the current cycle. Perform rotating coordinate transformation with the predicted rotor position angle to obtain the excitation current component and torque current component in the rotating coordinate system. S3. A sliding mode observer with gain adaptively adjusted with motor speed is used to estimate the back EMF of the motor. The estimated back EMF is low-pass filtered and the filter phase delay is compensated in real time according to the current speed. The rotor position angle and the estimated motor speed are output through phase-locked loop calculation. S4. Dynamically adjust the PWM carrier frequency according to the current operating speed of the motor, combine the target voltage vector to perform SVPWM modulation, configure the overmodulation control strategy to compress the zero vector action time and expand the modulation range, and generate three-phase bridge arm drive signals. S5. Based on the target speed and the estimated speed of the motor, a speed closed loop is constructed. Combined with the excitation current component and the torque current component, a current double closed loop is constructed, and the output control quantity drives the high-speed brushless motor to operate.

2. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The S1 step specifically includes: During the idle phase before motor startup, the current sampling value under the three-phase bridge arm fully off state is collected and stored in the register as the initial bias voltage; During motor operation, the sampling current at the zero vector action moment is calculated by moving average at fixed intervals, and the bias compensation value is dynamically updated. The sampled current is corrected by using the real-time updated bias compensation value to obtain the compensated three-phase stator current.

3. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The S2 step specifically includes: Perform Clarke transformation on the compensated three-phase stator current to obtain the current components in the two-phase stationary coordinate system; Based on the rotor position angle and estimated speed of the previous control cycle, the rotor position angle of the current cycle is predicted by linear interpolation; Using the predicted rotor position angle as input, the Park transformation is performed on the current components in the two-phase stationary coordinate system to obtain the excitation current component and torque current component in the rotating coordinate system.

4. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The S3 step specifically includes: Using the stator voltage setpoint and current sample value in the stationary coordinate system as input, a sliding mode observer is constructed, and the sliding mode gain of the sliding mode observer is adaptively adjusted with the motor speed. The back electromotive force estimate output by the sliding mode observer is low-pass filtered, and the phase delay caused by the filtering is compensated in real time according to the current rotational speed. The back EMF estimate after phase compensation is input into the phase-locked loop, and the rotor position angle and the estimated motor speed are output through closed-loop regulation.

5. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The S4 step specifically includes: The current operating speed of the motor is detected, and the PWM carrier frequency is reduced accordingly as the speed increases. The sector where the target voltage vector is located is determined by the positive or negative sign of the characteristic variables, and the action time of each vector is calculated based on the volt-second balance principle; When the magnitude of the target voltage vector exceeds the linear modulation range, overmodulation control is performed to compress the zero vector action time.

6. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The method also includes a three-stage smooth start procedure: During the rotor pre-positioning stage, a gradually increasing DC current is supplied to the two-phase windings of the motor to drag the rotor to the preset initial position. During the open-loop acceleration phase, the V / F control mode is used to increase the frequency and amplitude of the output voltage according to a preset slope, thereby driving the motor to accelerate synchronously. During the closed-loop switching phase, when the difference between the open-loop given speed and the observer estimated speed meets the preset conditions, the system switches to sensorless FOC closed-loop control through a weighted gradual change method.

7. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The method also includes an adaptive adjustment step for the commutation advance angle: The current motor speed and bus current are collected in real time. The basic value of the commutation advance angle is obtained based on the speed query, and the basic value of the commutation advance angle is dynamically corrected according to the bus current. Adjust the motor commutation timing based on the corrected commutation advance angle.

8. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The method also includes a temperature-controlled speed adjustment step: Collect the air temperature data from the air outlet of the blower, and obtain the real-time air temperature value after filtering; In warm air mode, a dual closed-loop temperature control structure with an outer temperature loop and an inner power loop is constructed, and a power control signal for the heating wire is output. When the outlet temperature exceeds the safety threshold, the heating wire power is reduced and the target motor speed is increased simultaneously. Once the temperature returns to the normal range, the original operating parameters are restored.

9. The speed control method for a high-speed hair dryer under low-voltage DC power supply according to claim 1, characterized in that, The method also includes multiple fault-tolerant protection steps: Real-time monitoring of bus current, motor speed and bus voltage triggers overcurrent protection, locked rotor protection and over / under voltage protection respectively; Real-time temperature data of motor windings and main control board is collected, and the motor speed and heat generation power are reduced in stages when the temperature exceeds the standard. All protection measures employ a tiered processing logic, prioritizing the elimination of abnormal states through derating.

10. A high-speed hair dryer powered by low-voltage DC power, used to execute the speed adjustment method of a high-speed hair dryer powered by low-voltage DC power as described in any one of claims 1 to 9, characterized in that, The low-voltage DC voltage is 24~48VDC, and the hair dryer includes: The low-voltage DC input module is used to connect to a low-voltage DC power supply. It has a built-in interface switch and reverse connection protection circuit to realize on-off control and reverse connection protection. The power conversion module is connected to the low-voltage DC input module and has a built-in DC-DC conversion circuit for converting the input DC voltage into multiple working voltages such as 12V and outputting them. The main control unit, connected to the power conversion module, uses an MCU microcontroller main control chip to run the speed control algorithm and output multiple control signals. The three-phase motor drive module is connected to the low-voltage DC input module and the main control unit respectively. It is adapted to 24~48VDC bus voltage input and is used to receive the PWM signal output by the main control unit to drive the 48V three-phase high-speed brushless motor to run. A temperature control sampling module, connected to the main control unit, uses an NTC temperature control circuit to collect air outlet temperature data and transmit it to the main control unit; The heating wire control module is connected to the low-voltage DC input module and the main control unit respectively, and is used to receive the control signal from the main control unit and adjust the heating power of the heating wire assembly. A negative ion generating module, connected to the main control unit, is used to receive start / stop control signals from the main control unit and release high-concentration negative ions; The human-computer interaction module, connected to the main control unit, includes a temperature button and a status indicator unit, used to receive user operation commands and display the operating status.

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