A fan speed control signal adaptive output, real-time calibration, and fault diagnosis system

Abstract

This invention discloses a fan speed control signal adaptive output, real-time calibration, and fault diagnosis system, belonging to the field of power electronics and industrial control equipment heat dissipation control. It achieves full electrical isolation between the control domain and the fan power domain through opto-isolation modules and bidirectional digital isolation modules, blocking power-side interference from entering the main control system. Through the PWM link verification inner loop and the analog feedforward calibration middle loop, it compensates for hardware distortion in the isolation link in real time. The secondary speed calibration outer loop compensates for nonlinear speed deviations caused by individual fan differences and aging, significantly improving speed control accuracy and adaptability to wide temperature environments. Simultaneously, through a switching module built with analog switches, it enables online switching between PWM speed control and analog speed control modes, and includes automatic fan type identification and fault diagnosis functions. This system solves the pain points of low accuracy, poor adaptability, and insufficient reliability in existing fan speed control circuits, and is suitable for heat dissipation control in industrial control equipment, servers, new energy storage, rail transit, and other scenarios.

Description

Technical Field

[0001] This invention belongs to the fields of power electronics technology and industrial heat dissipation control, and specifically relates to a fan speed control signal adaptive output, real-time calibration and fault diagnosis system. Background Technology

[0002] In industrial control equipment, server power supplies, new energy storage converters, and rail transit vehicle equipment, cooling fans are core components that ensure stable operation of the equipment. The accuracy, anti-interference ability, and reliability of the fan speed control system directly determine the operational stability of the entire equipment.

[0003] To prevent motor interference and surge impacts from the fan power side from entering the main control system, isolated fan speed control circuits are widely used in industrial settings. These circuits achieve electrical isolation between the control domain and the power domain through opto-isolation. However, existing isolated fan speed control circuits have the following unresolved core defects:

[0004] 1. Low speed regulation accuracy and poor environmental adaptability: The inherent transmission delay, temperature drift, and current transfer ratio (CTR) fluctuations caused by device aging of opto-isolated devices will directly cause distortion of the PWM signal duty cycle. The input and output duty cycle deviation can reach 5%-15%, and conventional shaping circuits cannot repair this dynamic deviation. In industrial wide-temperature scenarios, temperature drift will further aggravate the distortion and even cause speed regulation failure.

[0005] 2. Insufficient calibration capability, unable to achieve full-link closed loop: Most existing closed-loop speed control solutions only collect the fan's FG speed signal to perform a single speed closed loop, which can only compensate for the fan's own speed deviation. It cannot perform feedforward compensation for the hardware distortion of the isolation link itself. The calibration response speed is slow and cannot solve the two core problems of "isolation link hardware distortion" and "fan nonlinear deviation" at the same time. Moreover, most of them are single-point static calibration at the factory and cannot compensate for dynamic deviations caused by temperature drift and aging in real time online.

[0006] 3. Poor adaptability and inability to meet flexible configuration requirements on site: The output mode of the existing fan speed control circuit is fixed. It is configured as PWM speed control mode or analog speed control mode by mechanical jumper at the factory and cannot be modified online. It cannot be adapted to mainstream PWM speed control fans and 0-10V / 4-20mA analog speed control fans in industrial scenarios at the same time. Hardware circuit replacement is required for adaptation, resulting in high maintenance costs and low efficiency.

[0007] 4. Insufficient reliability and lack of redundancy protection mechanism: The existing solution only has basic overcurrent protection and cannot identify hidden faults such as PWM link distortion, analog sampling failure, speed signal disconnection, and power domain overheating. It lacks graded fault handling and redundancy switching mechanism. When a fault occurs, it is easy to cause the fan to stop, resulting in equipment overheating and shutdown, which cannot meet the functional safety requirements of high reliability industrial scenarios.

[0008] Therefore, developing an isolated fan speed control system that combines high speed regulation accuracy, strong environmental adaptability, flexible adaptability, and high reliability has become an urgent technical problem to be solved in this field. Summary of the Invention

[0009] Purpose of the invention: The purpose of this invention is to provide a fan speed control signal adaptive output, real-time calibration and fault diagnosis system, which can solve the problem of poor adaptability and inability to meet the flexible configuration requirements of the prior art.

[0010] Technical Solution: The present invention provides a fan speed control signal adaptive output, real-time calibration, and fault diagnosis system, comprising: a main control unit, an opto-isolation module, a bidirectional digital isolation module, a PWM shaping and driving module, a PWM-to-analog converter module, a mode switching module, an analog sampling module, a first PWM frequency measurement module, and a second PWM frequency measurement module; the input terminal of the main control unit is connected to the bidirectional digital isolation module, and the first output terminal of the main control unit is also connected to the bidirectional digital isolation module. The main control unit receives analog sampling signals, temperature sampling signals, and frequency signals fed back by the fan from the bidirectional digital isolation module and performs calibration calculations, outputting a mode switching digital control signal to the bidirectional digital isolation module; the second output terminal of the main control unit is connected to the PWM shaping and driving module through the opto-isolation module, and the main control unit outputs a PWM speed control signal to the PWM shaping and driving module; the output terminal of the PWM shaping and driving module is connected to the input terminal of the PWM-to-analog converter module, the first input terminal of the mode switching module, and the first PWM frequency measurement module, respectively. The input terminal is connected to the PWM shaping and driving module, which performs edge shaping and power amplification on the PWM speed control signal isolated by the opto-isolation module, and outputs a power-level PWM signal matching the fan power supply specifications to the PWM-to-analog module, the mode switching module, and the first PWM frequency measurement module. The output terminal of the PWM-to-analog module is connected to the input terminal of the analog sampling module and the second input terminal of the mode switching module. The PWM-to-analog module is used to convert the PWM signal into a DC analog voltage signal proportional to the PWM duty cycle, and transmit the DC analog voltage signal to the analog sampling module and the mode switching module. The control terminal of the mode switching module is connected to the first output terminal of the main control unit via a bidirectional digital isolation module, and the output terminal of the mode switching module is connected to the speed control pin of the fan to be controlled. The mode switching module is used to adaptively output either a PWM speed control signal or an analog speed control signal to the fan according to the digital control signal of the main control unit, so that the system can simultaneously adapt to both PWM speed control fans and analog speed control fans.

[0011] Furthermore, the main control unit has a built-in three-closed-loop calibration module. The input of the three-closed-loop calibration module is connected to the output of the reverse feedback channel of the bidirectional digital isolation module, and the output of the three-closed-loop calibration module is linked to the second output of the main control unit.

[0012] Furthermore, the three-loop calibration module includes a progressively configured PWM link verification inner loop, analog quantity feedforward calibration middle loop, and speed secondary calibration outer loop. The PWM link verification inner loop is used to correct the PWM speed control signal output by the main control unit in real time based on the comparison deviation between the power stage PWM signal and the initial target PWM signal, combined with the temperature drift compensation coefficient of the temperature sampling signal, to compensate for the hardware distortion and temperature drift deviation of the isolation and shaping link. The analog quantity feedforward calibration middle loop is used to verify the duty cycle accuracy twice based on the actual analog voltage sampling signal and the theoretical analog voltage value of the target duty cycle, combined with the temperature drift compensation coefficient, to compensate for the linearity error of the analog quantity conversion. The speed secondary calibration outer loop is used to correct the PWM output signal three times through an incremental PID control algorithm based on the deviation between the actual fan speed collected by the second PWM frequency measurement module and the target speed set by the main control unit, on the basis of the two-level calibration of the PWM link verification inner loop and the analog quantity feedforward calibration middle loop, to compensate for the nonlinear speed deviation of the fan.

[0013] Furthermore, the incremental PID control algorithm takes as input the deviation between the target speed and the actual fan speed, and outputs as the incremental correction value of the PWM signal duty cycle. The incremental PID control algorithm includes a proportional unit, an integral unit, and a derivative unit. The proportional unit is used to quickly respond to speed deviation, the integral unit is used to eliminate steady-state speed error, and the derivative unit is used to suppress speed overshoot.

[0014] Furthermore, the main control unit integrates an automatic fan type identification unit, a wide-temperature adaptive calibration unit, and a fault diagnosis unit. The automatic fan type identification unit, during the power-on initialization phase, sequentially outputs detection signals through the mode switching module and, combined with the feedback signal from the second PWM frequency measurement module, automatically identifies the fan to be controlled as a PWM speed-regulating fan or an analog speed-regulating fan, and automatically controls the mode switching module to switch to the corresponding operating mode. The wide-temperature adaptive calibration unit dynamically adjusts the temperature drift compensation coefficient of the feedforward calibration unit based on the ambient temperature, calling a pre-stored optocoupler parameter compensation table to achieve dynamic calibration across the entire temperature range of -40℃ to 125℃. The fault diagnosis unit monitors fault signals in real time at each stage of the three closed-loop calibration processes: the inner loop of the PWM link verification, the middle loop of the analog feedforward calibration, and the outer loop of the secondary speed calibration. It identifies faults in the PWM link, analog link, speed link, and over-temperature faults, and reports the fault information to the upper-level system.

[0015] Furthermore, the output of the analog sampling module is connected to the first input of the three-loop calibration module in the main control unit via a bidirectional digital isolation module. The analog sampling module is used to acquire the DC analog voltage signal output by the PWM to analog module and transmit it to the three-loop calibration module.

[0016] Furthermore, the input terminal of the first PWM frequency measurement module is connected to the output terminal of the PWM shaping and driving module, and the output terminal of the first PWM frequency measurement module is connected to the first reverse feedback channel of the bidirectional digital isolation module, for acquiring the actual duty cycle, frequency, and edge parameters of the power stage PWM signal; the input terminal of the second PWM frequency measurement module is connected to the FG speed feedback pin of the fan under control, and the output terminal of the second PWM frequency measurement module is connected to the second reverse feedback channel of the bidirectional digital isolation module, for acquiring the actual speed pulse signal of the fan, converting it into a speed digital signal, and using the speed digital signal as the actual speed of the fan.

[0017] Furthermore, the PWM shaping and driving module includes a two-stage high-speed CMOS inverter and a MOSFET power switching unit. The first-stage high-speed CMOS inverter is used to repair the edge distortion of the PWM signal after isolated transmission, and the second-stage high-speed CMOS inverter is used to improve the driving capability of the PWM signal. After two inversions, the original phase of the PWM signal is restored, ensuring the accuracy of duty cycle transmission. The MOSFET power switching unit uses an N-channel MOSFET to build a common-source switching circuit, converting the low-voltage logic PWM signal into a power-level PWM signal with amplitude matching the fan supply voltage, directly adapting to the level requirements of the fan speed control pin.

[0018] Furthermore, the mode switching module includes a dual-channel input analog switch. The first input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM shaping drive module, the second input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM to analog module, and the output terminal of the dual-channel input analog switch is connected to the speed control pin of the fan to be controlled. The main control unit controls the output mode of the dual-channel input analog switch through digital control signals to realize the mutual exclusion switching between PWM speed control mode and analog speed control mode.

[0019] Furthermore, both the first PWM frequency measurement module and the second PWM frequency measurement module include a pulse shaping circuit and a main control hardware timer unit;

[0020] The pulse shaping circuit is used to limit and shape the fan speed feedback pulse and the output PWM signal; the main control hardware timer unit is used to capture the frequency and duty cycle of the pulse signal and calculate the actual fan speed and the actual duty cycle of the output PWM.

[0021] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows:

[0022] (1) A progressive three-loop calibration system is constructed, consisting of an inner loop for PWM link verification, a middle loop for analog feedforward calibration, and an outer loop for secondary speed calibration. Simultaneously, a wide-temperature adaptive calibration unit is incorporated to collect ambient temperature in real time and call upon a pre-stored optocoupler parameter compensation table to dynamically correct the temperature drift compensation coefficient. This completely solves the CTR fluctuation problems caused by transmission delay, temperature drift, and device aging of opto-isolated devices, overcomes the inherent deviation of 5%~15% in the PWM duty cycle of traditional circuits, and compensates for the shortcomings of conventional shaping circuits in repairing dynamic deviations, exacerbating signal distortion, and even causing speed control failure under wide industrial temperature environments. It effectively suppresses signal distortion and temperature drift interference in the isolation link, significantly reduces the PWM input / output duty cycle deviation, achieves adaptive dynamic compensation across the entire temperature range of -40℃ to 125℃, maintains stable speed control performance under extreme high and low temperature conditions, and significantly improves speed control accuracy and adaptability to wide industrial temperature environments.

[0023] (2) Breaking away from the traditional single FG speed closed-loop architecture, this system achieves full-link closed-loop control of isolated link feedforward calibration, analog-to-digital conversion calibration, and fan speed post-calibration. It introduces an incremental PID algorithm for precise speed correction and adopts an online real-time dynamic calibration mode throughout the process. This addresses the shortcomings of existing solutions that can only compensate for fan speed deviation and cannot provide feedforward compensation for isolated link hardware distortion, overcoming the two major challenges of not being able to simultaneously handle "isolated link hardware distortion" and "fan nonlinear deviation." It also abandons the factory single-point static calibration mode, solving the problem of not being able to compensate for temperature drift and dynamic deviations caused by device aging online. The calibration covers the entire link of signal isolation, analog-to-digital conversion, and speed feedback, significantly improving the calibration response speed. It can simultaneously offset the inherent errors of the hardware link and the nonlinear speed deviations caused by individual fan differences, aging, and load fluctuations, providing real-time online compensation for temperature drift and aging drift throughout the process, eliminating the lag and limitations of static calibration.

[0024] (3) A hardware mode switching module is built using a dual-channel analog switch, integrating an automatic fan type identification unit. Upon power-up, it automatically detects the fan type and autonomously controls the online switching of modes. This overcomes the drawbacks of traditional speed control circuits, which have fixed output modes, rely on mechanical jumpers for manual configuration, and cannot be modified online. It also solves the problem of not being able to simultaneously support mainstream industrial PWM speed control fans and 0-10V / 4-20mA analog speed control fans, requiring hardware replacement for on-site adaptation, resulting in high maintenance costs and low configuration efficiency. No manual modification of hardware jumpers or circuit replacement is required. Upon power-up, it automatically identifies the fan type and adaptively switches to the corresponding speed control mode. It is compatible with two types of mainstream industrial speed control fans, eliminating the need for hardware modification and manual configuration on-site, greatly improving adaptation flexibility, and significantly reducing on-site maintenance costs and equipment modification cycles.

[0025] (4) A full-link fault diagnosis unit is built based on the three-closed-loop calibration link, which can accurately identify four major types of faults: PWM link, analog link, speed link, and power domain over-temperature, and is equipped with a three-level graded fault handling mechanism. This makes up for the shortcomings of the existing solution, which only has basic overcurrent protection and cannot identify hidden faults such as link distortion, sampling failure, speed disconnection, and over-temperature; it solves the problem that without graded processing logic, faults can easily cause fan stoppage and equipment overheating shutdown, making it difficult to meet industrial functional safety requirements. It realizes real-time monitoring of the entire link operation status and accurate location of hidden faults, and has the ability to provide fault early warning and emergency shutdown graded protection. It eliminates the risk of fans stopping without reason and the whole equipment overheating shutdown, and meets the functional safety design requirements of high reliability scenarios such as industrial control, energy storage, and rail transit. Attached Figure Description

[0026] Figure 1 This is a system block diagram of the present invention;

[0027] Figure 2 This is a circuit diagram of the opto-isolation module in this invention;

[0028] Figure 3 This is a circuit diagram of the PWM shaping and driving module in this invention;

[0029] Figure 4 This is a flowchart of the automatic fan type identification process in this invention;

[0030] Figure 5 This is the logic diagram for the three-closed-loop real-time calibration and full-link fault diagnosis in this invention. Detailed Implementation

[0031] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0032] like Figure 1 As shown, the fan speed control signal adaptive output, real-time calibration and fault diagnosis system of the present invention includes: a main control unit, an opto-isolation module, a bidirectional digital isolation module, a PWM shaping and driving module, a PWM to analog quantity conversion module, a mode switching module, an analog quantity sampling module, a first PWM frequency measurement module, a second PWM frequency measurement module, a temperature sampling module and a three-closed-loop calibration module.

[0033] The main control unit's input is connected to a bidirectional digital isolation module, and its first output is also connected to the same module. The main control unit receives analog sampling signals, temperature sampling signals, and frequency signals from the fan feedback from the bidirectional digital isolation module, performs calibration calculations, and outputs a mode-switching digital control signal to the module. The second output of the main control unit is connected to a PWM shaping and driving module via an opto-isolation module, and the main control unit outputs a PWM speed control signal to this module. In this embodiment, the main control unit is built using an industrial-grade MCU, with a built-in PWM generator, hardware timer capture unit, and processing unit. It outputs the target PWM speed control signal and mode-switching control signal, receives the isolated feedback signal, and performs calibration calculations to achieve full-process control of the system.

[0034] The main control unit uses an STM32F103C8T6 industrial-grade MCU, which integrates one advanced timer (supporting 25kHz PWM output), three 16-bit general-purpose timers (supporting pulse capture), and four GPIO digital output ports. Its operating temperature range is -40℃ to 105℃, meeting the requirements of industrial applications. The main control unit is powered by a 3.3V logic power supply in the control domain, grounded at the control domain GND, and completely isolated from the fan power domain GND-F.

[0035] The input terminal of the opto-isolation module is connected to the second output terminal (PWM output terminal) of the main control unit, and the output terminal of the opto-isolation module is connected to the input terminal of the PWM shaping and driving module. The opto-isolation module is used to achieve full electrical isolation between the control domain and the fan power domain of the main control unit and to transmit PWM speed control signals. In this embodiment, the opto-isolation module adopts a high-speed push-pull output type isolation optocoupler. Its input side power supply is the 3.3V / 5V logic power supply of the control domain, and the input side is connected in series with a current-limiting resistor to protect the internal light-emitting diode. The output side power supply is the fan power domain power supply, which achieves full electrical isolation between the control domain and the fan power domain of the main control unit. At the same time, it supports the distortion-free transmission of mainstream 1~25kHz fan speed control PWM signals and blocks motor interference and surge impacts from the power side from entering the main control unit.

[0036] like Figure 2 As shown, the opto-isolation module uses a TLP5774 high-speed push-pull output type isolation optocoupler, supporting a maximum signal transmission rate of 1Mbps, fully adapting to the transmission requirements of a 25kHz fan speed control PWM signal. Pin 3 (cathode) of the optocoupler is connected to the PWM output terminal of the main control unit through a 300Ω current-limiting resistor; pin 1 (anode) is connected to the control domain VCC; pin 6 (VCC) is connected to the 24V power supply VFAN+ of the fan power domain; pin 4 (GND) is connected to the power domain GND-F; and pin 5 (output terminal) is connected to the input terminal of the PWM shaping drive module, achieving full electrical isolation between the control domain and the power domain, with an isolation withstand voltage of up to 2500VAC.

[0037] The bidirectional digital isolation module is a multi-channel bidirectional electrical isolation device with an isolation withstand voltage of not less than 2500VAC. It supports industrial wide-temperature operation from -40℃ to 125℃ and includes at least one forward control transmission channel and three reverse feedback transmission channels to achieve full-link bidirectional electrical isolation between the control domain of the main control unit and the fan power domain. The input of the forward control transmission channel is connected to the digital control output (i.e., the first output) of the main control unit, and the output of the forward control transmission channel is connected to the control terminal of the analog switching module. The forward control transmission channel is used to isolate the transmission of mode switching control signals. The three reverse feedback channels isolate and transmit PWM parameters, fan speed, and analog sampling feedback signals to the main control unit, respectively, completely preventing power-side interference from entering the control domain of the main control unit.

[0038] The bidirectional digital isolation module uses the NSI8241W0-DSWR four-channel bidirectional digital isolator, with an isolation withstand voltage of 3000V, a maximum transmission rate of 150Mbps, and an operating temperature range of -40℃ to 125℃. The channel configuration is as follows: the forward channel of the NSI8241W0-DSWR transmits mode switching control signals; reverse channel 1 transmits power stage PWM signals; reverse channel 2 transmits fan speed signals (FG); and reverse channel 3 transmits analog sampling signals. The isolator's input side is powered by a 3.3V control domain power supply, and the output side is powered by a 3.3V power domain regulated power supply. Both power supply pins are equipped with 0.1μF ceramic decoupling capacitors to ensure power stability.

[0039] The output of the PWM shaping and driving module is connected to the input of the PWM-to-analog converter module, the first input of the mode switching module, and the input of the first PWM frequency measurement module, respectively. The PWM shaping and driving module is used to shape the edges and amplify the power of the PWM speed control signal isolated by the opto-isolation module, outputting a power-level PWM signal matching the fan power supply specifications to the PWM-to-analog converter module, the mode switching module, and the first PWM frequency measurement module. In this embodiment, the PWM shaping and driving module includes two stages of high-speed CMOS inverters and a MOSFET power switching unit. The first stage of the high-speed CMOS inverter is used to repair edge distortion of the PWM signal after isolation transmission and filter out noise glitches during transmission. The second stage of the high-speed CMOS inverter is used to improve the driving capability of the PWM signal and match the input impedance of the subsequent circuit. After two inversions, the original phase of the PWM signal is restored, ensuring the accuracy of the duty cycle transmission. The MOSFET power switching unit uses an N-channel MOSFET to build a common-source switching circuit, converting the low-voltage logic PWM signal into a power-level PWM signal with an amplitude matching the fan power supply voltage (12V / 24V / 48V), directly adapting to the level requirements of the fan speed control pin.

[0040] like Figure 3As shown, the PWM shaping and driving module includes a two-stage inverting shaping unit and a MOSFET power switching unit. The two-stage inverting shaping unit uses two 74AHC1G04GV high-speed CMOS inverters to build a two-stage inverting circuit. The input of the first-stage inverter is connected to the PWM output of the opto-isolation module, and the output is connected to the input of the second-stage inverter. After two inversions, the original phase of the PWM signal is restored, and the signal edge distortion after isolation transmission is corrected, improving the driving capability of the PWM signal. The inverter is powered by 24V VFAN+ regulated by a 5.1V Zener diode BZX84-C5V1 to ensure stable logic levels. The MOSFET power switching unit uses a BSS123 N-channel MOSFET to build a common-source switching circuit. The gate is connected to the output of the second-stage inverter through a 300Ω current-limiting resistor, and the gate is also connected to GND-F through a 4.7K pull-down resistor to prevent the MOSFET from being mis-turned on. The drain is connected to 24V VFAN+ through a 15K pull-up resistor, and the source is connected to GND-F. The drain outputs a 24V power stage PWM signal to match the speed control pin level requirements of a 24V fan.

[0041] The output of the PWM to analog module is connected to the input of the analog sampling module and the second input of the mode switching module. The PWM to analog module converts the PWM signal into a DC analog voltage signal proportional to the PWM duty cycle and transmits the DC analog voltage signal to the analog sampling module and the mode switching module. In this embodiment, the PWM to analog module is built using a high-order RC low-pass filter circuit. The cutoff frequency of the filter circuit is lower than 1 / 10 of the PWM signal frequency, which smoothly converts the PWM square wave signal into a DC analog voltage signal. The output DC voltage amplitude equals the fan supply voltage multiplied by the PWM signal duty cycle, thus achieving a simple conversion from PWM signal to analog signal.

[0042] The PWM to analog converter module is built using an active low-pass filter circuit. The core is a TPA1834 four-channel rail-to-rail industrial-grade operational amplifier. The circuit is entirely located within the fan power domain and is powered by a single power supply (VAN+) with the power domain ground (GND-F) as the reference ground. The first stage is a non-inverting input buffer using a voltage follower architecture to enhance the PWM signal driving capability. The second stage is a first-order RC low-pass filter circuit, built with 2KΩ precision resistors and 10μF ceramic capacitors. Its cutoff frequency is approximately 8Hz, far below the 25kHz speed-regulating PWM frequency, smoothly converting the PWM square wave signal into a low-ripple DC voltage. The output voltage is consistent with the PWM signal. The duty cycle exhibits a strictly linear relationship; the third stage is an output buffer, also employing a voltage follower architecture, used to eliminate the influence of the input impedance of the analog sampling and analog switch in the subsequent stage on the filtering effect, thereby improving the load-carrying capacity and stability of the analog signal; the module finally outputs an analog signal, which is sent to the analog switch mode switching module as an analog speed regulation drive signal, and another path is sent to the analog sampling module to provide accurate analog feedback data for the feedforward calibration inner loop, ensuring calibration accuracy.

[0043] The mode switching module's control terminal is connected to the main control unit's digital control output terminal (i.e., the first output terminal) via a bidirectional digital isolation module. The output terminal of the mode switching module is connected to the speed control pin of the fan under control. The mode switching module is used to adaptively output PWM speed control signals or analog speed control signals to the fan according to the digital control signals from the main control unit, enabling the system to simultaneously adapt to both PWM speed control fans and analog speed control fans. In this embodiment, the mode switching module is constructed using a dual-channel input analog switch; the first input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM shaping drive module, the second input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM-to-analog module, and the output terminal of the dual-channel input analog switch is connected to the speed control pin of the fan under control. The main control unit controls the output mode of the dual-channel input analog switch through digital control signals to achieve mutually exclusive switching between PWM speed control mode and analog speed control mode.

[0044] The dual-channel input analog switch is built using a single-pole double-throw integrated low on-resistance analog switch chip. The mode switching module supports a wide voltage signal input range of 1.8V to 24V. Its two independent signal input terminals are: the first signal input terminal is connected to the output terminal of the PWM shaping module (PWM speed control channel), and the second signal input terminal is connected to the output terminal of the PWM to analog quantity module (analog quantity speed control channel). Its common output terminal is connected to the speed control pin of the fan under control. Its control terminal is connected to the output terminal of the positive control transmission channel of the bidirectional digital isolation module. The main control unit controls the complementary on / off state of the two channels through digital control signals to achieve mutually exclusive switching between PWM speed control mode and analog quantity speed control mode, replacing the original mechanical jumpers and supporting online digital configuration.

[0045] The mode switching module is built using the ADI ADG419 single-pole double-throw analog switch chip, supporting 0~44V signal input, fully matching the speed control level requirements of a 24V fan. The chip's IN pin (control terminal) is connected to the positive control channel output of the bidirectional digital isolation module, the S1 pin is connected to the output of the PWM shaping module (PWM speed control channel), the S2 pin is connected to the output of the PWM to analog converter module (analog speed control channel), and the D pin (common output terminal) is connected to the fan's speed control pin PWM-FAN. When the IN pin is low, S1 and D are conducting, and the system operates in PWM speed control mode; when the IN pin is high, S2 and D are conducting, and the system operates in analog speed control mode.

[0046] The output of the analog sampling module is connected to the first input of the three-loop calibration module in the main control unit via a bidirectional digital isolation module. The analog sampling module is used to acquire the DC analog voltage signal output by the PWM to analog module and transmit it to the three-loop calibration module. (The last sentence is a repetition of the previous one and can be omitted.)

[0047] The analog sampling module is located in the fan power domain and is built using an ADC chip with a precision of 16 bits or higher. Its input is connected to the output of the PWM to analog module, and its output is connected to the third reverse feedback channel of the bidirectional digital isolation module. It is used to collect the actual analog voltage signal output by the PWM to analog module, convert it into a digital sampling signal, and then transmit it to the main control unit through isolation. This avoids the influence of cross-ground common-mode voltage on the sampling accuracy and accurately represents the actual duty cycle of the PWM signal after isolation drive.

[0048] The analog sampling module is located in the fan power domain and is built using the SGM58031XMS10G / TR, a 16-bit high-precision ADC chip. The ADC is powered by a 5V regulated power supply in the power domain. The analog input terminal uses a high-precision resistor voltage divider circuit to scale the 0-24V analog voltage signal to 0-2.5V to match the ADC's input range. The ADC transmits the sampled digital signal to the main control unit via an I2C interface and a bidirectional digital isolation module to avoid the influence of cross-ground common-mode voltage on the sampling accuracy. The sampling resolution can reach 0.5mV.

[0049] The input of the first PWM frequency measurement module is connected to the output of the PWM shaping and driving module, and the output of the first PWM frequency measurement module is connected to the first reverse feedback channel of the bidirectional digital isolation module. This module is used to acquire the actual duty cycle, frequency, and edge parameters of the power stage PWM signal. The input of the second PWM frequency measurement module is connected to the FG speed feedback pin of the fan under control, and the output of the second PWM frequency measurement module is connected to the second reverse feedback channel of the bidirectional digital isolation module. This module is used to acquire the actual fan speed pulse signal, convert it into a digital speed signal, and use this digital speed signal as the actual fan speed to provide feedback data for the outer loop of the secondary speed calibration. In this embodiment, the first and second PWM frequency measurement modules include a pulse shaping circuit and a main control hardware timer unit. The pulse shaping circuit is used to limit and shape the fan speed feedback pulse and the output PWM signal. The main control hardware timer unit is used to capture the frequency and duty cycle of the pulse signal and calculate the actual fan speed and the actual duty cycle of the output PWM. The pulse shaping circuit limits, debouncing, and smooths the edges of the PWM signal. The main control hardware timer capture unit automatically captures the rising and falling edges of the pulse and accurately measures the actual duty cycle, frequency, and edge parameters of the output PWM signal, providing reference data for PWM link inner loop verification.

[0050] The first and second PWM frequency measurement modules use a TLV3501AID comparator to build a pulse shaping circuit, which works in conjunction with the main controller's hardware timer capture unit to achieve frequency measurement. The PWM signal or FG speed pulse signal is connected to the positive input of the comparator after passing through a voltage divider resistor, and the inverting input of the comparator is connected to a 2.5V reference voltage. The output is connected to the inverting feedback channel input of the bidirectional digital isolation module, and after isolation, it is connected to the main controller's timer capture pin. The comparator limits, debounces, and smooths the edges of the pulse signal. The main controller automatically captures the rising and falling edges of the pulse through the timer's input capture mode, and accurately calculates the pulse frequency, period, and duty cycle.

[0051] The main control unit incorporates a three-loop calibration module. The input of this module is connected to the output of the reverse feedback channel of the bidirectional digital isolation module, and its output is linked to the second output (PWM output) of the main control unit. The three-loop calibration module comprises a progressively configured inner loop for PWM link verification, a middle loop for analog feedforward calibration, and an outer loop for secondary speed calibration, as detailed below:

[0052] The PWM link verification inner loop is used to correct the PWM speed control signal output by the main control unit in real time based on the comparison deviation between the power stage PWM signal and the initial target PWM signal, combined with the temperature drift compensation coefficient of the temperature sampling signal. This compensates for the hardware distortion and temperature drift deviation of the isolation and shaping links. Specifically, the PWM link verification inner loop compares the actual parameters of the power stage PWM signal collected by the first PWM frequency measurement module with the initial target PWM signal output by the main control unit in real time. Combined with the temperature drift compensation coefficient output by the wide-temperature adaptive calibration unit, it calculates the duty cycle deviation and delay asymmetry of the isolation and shaping links, and corrects the PWM pulse width output by the main control unit in real time, compensating for the hardware distortion and temperature drift deviation of the isolation link from the source.

[0053] The analog signal feedforward calibration loop is used to compensate for the linearity error of analog signal conversion by comparing the actual analog voltage sampling signal with the theoretical analog voltage value corresponding to the target duty cycle, and combining the temperature drift compensation coefficient to verify the duty cycle accuracy a second time. Specifically, the analog signal feedforward calibration loop performs a differential comparison between the actual analog voltage signal collected by the analog sampling module and the theoretical analog voltage value corresponding to the target duty cycle, combines the temperature drift compensation coefficient to verify the duty cycle accuracy a second time, calculates the linearity error of analog signal conversion, and corrects the PWM duty cycle output by the main control for the second time, providing a calibration benchmark for analog speed control mode.

[0054] The secondary speed calibration outer loop is used to correct the PWM output signal three times based on the deviation between the actual fan speed collected by the second PWM frequency measurement module and the target speed set by the main control unit. This is done on top of the two-stage calibration process of the PWM link verification inner loop and the analog feedforward calibration middle loop. The incremental PID control algorithm is used to compensate for the nonlinear speed deviation caused by individual fan differences, aging, and load fluctuations. The PWM link verification inner loop, the analog feedforward calibration middle loop, and the secondary speed calibration outer loop can improve speed regulation accuracy and environmental adaptability. In this embodiment, the input of the incremental PID control algorithm is the deviation between the target speed and the actual fan speed, and the output is the incremental correction value of the PWM signal duty cycle. The incremental PID control algorithm includes a proportional unit, an integral unit, and a derivative unit. The proportional unit is used to quickly respond to speed deviations, the integral unit is used to eliminate steady-state speed error, and the derivative unit is used to suppress speed overshoot.

[0055] The following is the three-closed-loop real-time calibration workflow:

[0056] like Figure 5 As shown, after the system enters the normal speed regulation process, the three-closed-loop calibration module runs in real time with a 10ms cycle, and the workflow is as follows:

[0057] The main control unit receives the target speed command from the upper-level system, converts it into the corresponding target PWM duty cycle, and outputs the initial target PWM signal;

[0058] The temperature sampling module collects the ambient temperature in the power domain in real time, and the wide-temperature adaptive calibration unit calls the pre-stored optocoupler parameter compensation table to update the temperature drift compensation coefficient.

[0059] PWM link verification inner loop operation: The first channel of the PWM frequency measurement module collects the actual duty cycle and frequency parameters of the shaped PWM, compares them with the initial target PWM signal in real time, calculates the deviation of the isolation and shaping link in combination with the temperature drift compensation coefficient, corrects the PWM pulse width output by the main control in real time, and compensates for link distortion and temperature drift deviation.

[0060] Analog signal feedforward calibration loop operation: The analog signal sampling module collects the actual DC voltage of the PWM to analog signal conversion, compares it with the theoretical voltage corresponding to the target duty cycle, calculates the linear deviation in combination with the temperature drift compensation coefficient, and corrects the PWM output duty cycle in the second step.

[0061] Secondary speed calibration outer loop operation: The second channel of the PWM frequency measurement module acquires the fan FG speed pulse, calculates the actual speed, compares it with the target speed to calculate the speed deviation, and uses an incremental PID algorithm to correct the PWM output duty cycle three times on the basis of the first two calibrations to compensate for the fan nonlinear deviation;

[0062] The system executes the above calibration process cyclically to achieve real-time closed-loop speed regulation.

[0063] The main control unit integrates an automatic fan type identification unit, a wide-temperature adaptive calibration unit, and a fault diagnosis unit. For example... Figure 4As shown, the automatic fan type identification unit automatically identifies the type of fan to be controlled and automatically controls the mode switching module to switch to the corresponding working mode. It has high adaptability and can meet flexible on-site configuration needs without requiring manual on-site configuration. After the system is powered on, the main control unit completes reset, clock configuration, and peripheral initialization. Hardware such as the opto-isolation module, bidirectional digital isolation module, and PWM shaping drive module complete self-tests. The automatic fan type identification unit starts and enters the automatic identification process. The main control unit sends a low-level control signal to the mode switching module through the positive control channel of the bidirectional digital isolation module, switching the analog switch to the PWM speed control channel and outputting a standard detection signal: the main control unit outputs a standard PWM detection signal with fixed parameters, which, after opto-isolation and PWM shaping drive, is output to the fan speed control pin through the mode switching module. The second PWM frequency measurement module begins to collect the pulse signal from the fan's FG speed feedback pin. If a stable and valid speed pulse signal is detected, and the speed and the output PWM duty cycle are linearly related, it is determined to be a PWM speed control fan. If no valid speed pulse is detected, or if the speed and PWM duty cycle do not show a clear linear relationship, the analog speed control fan detection phase begins. To avoid fan surges caused by level jumps, the main control unit first smoothly reduces the current PWM duty cycle to 0, then sends a high-level control signal to switch the analog switch to the analog speed control channel. The main control unit outputs a 50% duty cycle PWM signal, which is converted into a corresponding DC voltage by the PWM-to-analog converter and output to the fan speed control pin. The second PWM frequency measurement module again acquires the fan FG speed feedback signal and monitors it continuously for 500ms. If a stable and valid speed pulse signal is detected, and the speed and the output analog voltage show a linear relationship, it is determined to be an analog speed control fan. If no valid speed pulse is detected, it is determined that the fan is not connected or there is a hardware fault, and a "fan connection fault" alarm is reported to the higher-level system. The wide-temperature adaptive calibration unit is used to call the pre-stored optocoupler parameter compensation table according to the power domain ambient temperature collected by the temperature sampling module, dynamically adjust the temperature drift compensation coefficient of the three closed-loop calibration module, and simultaneously apply it to the inner loop of PWM link verification and the middle loop of analog feedforward calibration to achieve dynamic calibration in the full temperature range of -40℃ to 125℃.

[0064] The fault diagnosis unit is used to monitor fault signals in real time at each stage of the three closed-loop calibration processes: the inner loop of PWM link verification, the middle loop of analog feedforward calibration, and the outer loop of speed secondary calibration. It identifies four types of faults: PWM link faults, analog link faults, speed link faults, and over-temperature faults, and reports the fault information to the upper-level system. It executes a three-level fault handling mechanism: Level 1 correctable faults trigger software compensation and early warning; Level 2 mode failure faults trigger mode soft switching and fault alarms; Level 3 severe faults trigger emergency shutdown protection, comprehensively ensuring the safety and reliability of system operation.

[0065] like Figure 5 As shown, the end-to-end fault diagnosis and tiered handling process is as follows:

[0066] During system operation, the fault diagnosis and protection unit monitors fault signals in real time at each stage of the three-closed-loop calibration and executes a three-level fault handling mechanism:

[0067] Fault identification: It can identify four types of core faults: PWM link fault (duty cycle deviation exceeds limit, waveform loss, channel failure), analog link fault (ADC failure, sampling disconnection, linearity deviation), speed link fault (fan stall, FG disconnection, speed runaway), and power domain over-temperature fault (ambient temperature exceeds rated threshold).

[0068] Level 1 fault handling: For minor faults that can be corrected, such as small temperature drift deviations or minor interference glitches, trigger the software compensation algorithm, continuously monitor the fault status, and report early warning signals to the superior system.

[0069] Level 2 fault handling: For faults that cause the current mode to fail, such as no output from the PWM link or failure of analog signal sampling, a soft switching process is triggered to automatically and seamlessly switch to the backup speed control mode to keep the fan running normally, while reporting a fault alarm signal to the upper-level system.

[0070] Level 3 fault handling: For serious faults, such as fan stall, severe overheating of the power domain, or hardware short circuit, immediately shut down the speed control output, trigger an emergency shutdown, and simultaneously report an emergency fault signal to the superior system to prevent equipment damage.

[0071] The main control unit also integrates a soft switching control unit, which is used to control the gradual transition of the PWM signal duty cycle or analog output voltage during mode switching. Specifically, the soft switching control unit first smoothly reduces the current PWM duty cycle to 0 in steps of 10% / 20ms, and then controls the analog switch to complete the channel switching. After the switching is completed, the speed control signal is gradually increased to the target value in steps of 10% / 20ms to avoid sudden changes in fan speed, noise impact and device damage caused by the level jump at the moment of switching.

[0072] The temperature sampling module is located in the fan power domain. It uses a 10kΩ NTC thermistor and a 10kΩ 0.5% precision metal film resistor to build a voltage divider circuit. The NTC thermistor is placed on the power domain circuit board, close to the bidirectional digital isolation module, the PWM shaping drive module and the fan interface. Its output is connected to the ADC chip in the analog sampling module to accurately acquire the operating ambient temperature of the core components in the power domain. The voltage-divided signal is connected to the second analog input of the SGM58031XMS10G / TR, and after ADC conversion and digital isolation, it is transmitted to the main control unit to provide temperature data for wide-temperature adaptive calibration.

[0073] Fan interface and protection circuit: The fan speed control pin interface is equipped with a P6SMB36CA TVS diode and an S07K30-CN varistor to form a two-stage protection circuit to suppress interface surges, ESD static electricity, and overvoltage impacts, and protect the analog switch and subsequent circuits; the fan power supply circuit is connected in series with a 1A self-resetting fuse to achieve overcurrent protection.

[0074] This invention achieves full electrical isolation between the control domain and the fan power domain through opto-isolation modules and bidirectional digital isolation modules, blocking power-side interference from entering the main control system. It compensates for hardware distortion in the isolation link in real time through an inner loop of PWM link verification and a middle loop of analog feedforward calibration. It also compensates for nonlinear speed deviations caused by individual fan differences and aging through an outer loop of secondary speed calibration, significantly improving speed control accuracy and adaptability to wide temperature environments. Furthermore, it utilizes a mode switching module built with analog switches to achieve online switching between PWM and analog speed control modes, along with automatic fan type identification and fault diagnosis functions. This invention addresses the pain points of low accuracy, poor adaptability, and insufficient reliability in existing fan speed control circuits, and can be widely applied to heat dissipation control in industrial control equipment, servers, new energy storage, rail transit, and other scenarios.

[0075] This invention solves the dual problems of isolation link distortion and fan nonlinear deviation through a three-closed-loop calibration architecture, realizes online adaptive configuration of speed control mode through analog switch switching, and is equipped with redundant protection function to comprehensively improve the performance and reliability of fan speed control system.

Claims

1. A fan speed regulation signal adaptive output, real-time calibration and fault diagnosis system, characterized in that: include: Main control unit, opto-isolation module, bidirectional digital isolation module, PWM shaping and driving module, PWM to analog quantity module, mode switching module, analog quantity sampling module, first PWM frequency measurement module, second PWM frequency measurement module; The input terminal of the main control unit is connected to the bidirectional digital isolation module, and the first output terminal of the main control unit is also connected to the bidirectional digital isolation module. The main control unit receives the analog sampling signal, temperature sampling signal, and frequency signal fed back by the fan from the bidirectional digital isolation module and performs calibration calculations. It then outputs a mode switching digital control signal to the bidirectional digital isolation module. The second output terminal of the main control unit is connected to the PWM shaping and driving module through an opto-isolation module, and the main control unit outputs a PWM speed regulation signal to the PWM shaping and driving module. The output terminal of the PWM shaping and driving module is connected to the input terminal of the PWM to analog module, the first input terminal of the mode switching module, and the input terminal of the first PWM frequency measurement module, respectively. The PWM shaping and driving module is used to perform edge shaping and power amplification on the PWM speed regulation signal isolated by the opto-isolation module, and output a power-level PWM signal that matches the fan power supply specifications to the PWM to analog module, the mode switching module, and the first PWM frequency measurement module. The output terminal of the PWM to analog module is connected to the input terminal of the analog sampling module and the second input terminal of the mode switching module. The PWM to analog module is used to convert the PWM signal into a DC analog voltage signal that is proportional to the PWM duty cycle, and transmit the DC analog voltage signal to the analog sampling module and the mode switching module. The control terminal of the mode switching module is connected to the first output terminal of the main control unit via a bidirectional digital isolation module. The output terminal of the mode switching module is connected to the speed control pin of the fan to be controlled. The mode switching module is used to adaptively output a PWM speed control signal or an analog speed control signal to the fan according to the digital control signal of the main control unit, so that the system can simultaneously adapt to both PWM speed control fans and analog speed control fans.

2. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The main control unit has a built-in three-closed-loop calibration module. The input of the three-closed-loop calibration module is connected to the output of the reverse feedback channel of the bidirectional digital isolation module, and the output of the three-closed-loop calibration module is linked to the second output of the main control unit.

3. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 2, characterized in that: The three-closed-loop calibration module includes a PWM link verification inner loop, an analog quantity feedforward calibration middle loop, and a speed secondary calibration outer loop, which are progressively set from the inside out. The inner loop of the PWM link verification is used to correct the PWM speed regulation signal output by the main control unit in real time based on the comparison deviation between the power stage PWM signal and the initial target PWM signal, combined with the temperature drift compensation coefficient of the temperature sampling signal, to compensate for the hardware distortion and temperature drift deviation of the isolation and shaping link. The analog quantity feedforward calibration loop is used to verify the duty cycle accuracy twice based on the actual analog voltage sampling signal and the theoretical analog voltage value of the target duty cycle, combined with the temperature drift compensation coefficient, to compensate for the linear error of analog quantity conversion. The outer loop of the secondary speed calibration is used to correct the PWM output signal three times through an incremental PID control algorithm based on the deviation between the actual fan speed collected by the second PWM frequency measurement module and the target speed set by the main control unit, on the basis of the two-stage calibration of the inner loop of PWM link verification and the middle loop of analog quantity feedforward calibration, in order to compensate for the nonlinear speed deviation of the fan.

4. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 3, characterized in that: The incremental PID control algorithm takes the deviation between the target speed and the actual fan speed as input and outputs the incremental correction value of the PWM signal duty cycle. The incremental PID control algorithm includes a proportional unit, an integral unit, and a derivative unit. The proportional unit is used to quickly respond to speed deviations, the integral unit is used to eliminate steady-state speed error, and the derivative unit is used to suppress speed overshoot.

5. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The main control unit integrates a fan type automatic identification unit, a wide temperature adaptive calibration unit, and a fault diagnosis unit. The automatic fan type identification unit is used to automatically identify whether the fan to be controlled is a PWM speed-regulating fan or an analog speed-regulating fan by sequentially outputting detection signals through the mode switching module during the power-on initialization phase, combined with the feedback signal of the second PWM frequency measurement module, and automatically control the mode switching module to switch to the corresponding working mode. The wide-temperature adaptive calibration unit is used to call the pre-stored optocoupler parameter compensation table according to the ambient temperature, and dynamically adjust the temperature drift compensation coefficient of the feedforward calibration unit to achieve dynamic calibration in the full temperature range of -40℃ to 125℃. The fault diagnosis unit is used to monitor fault signals in real time at each stage of the three closed-loop calibration processes: the inner loop of PWM link verification, the middle loop of analog quantity feedforward calibration, and the outer loop of speed secondary calibration. It identifies faults in the PWM link, analog quantity link, speed link, and over-temperature faults, and reports the fault information to the upper-level system.

6. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The output of the analog sampling module is connected to the first input of the three-loop calibration module in the main control unit via a bidirectional digital isolation module. The analog sampling module is used to collect the DC analog voltage signal output by the PWM to analog module and transmit it to the three-loop calibration module.

7. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The input terminal of the first PWM frequency measurement module is connected to the output terminal of the PWM shaping and driving module, and the output terminal of the first PWM frequency measurement module is connected to the first reverse feedback channel of the bidirectional digital isolation module, which is used to acquire the actual duty cycle, frequency and edge parameters of the power stage PWM signal. The input terminal of the second PWM frequency measurement module is connected to the FG speed feedback pin of the fan under control, and the output terminal of the second PWM frequency measurement module is connected to the second reverse feedback channel of the bidirectional digital isolation module. It is used to collect the actual speed pulse signal of the fan and convert it into a speed digital signal. The speed digital signal is used as the actual speed of the fan.

8. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The PWM shaping and driving module includes two-stage high-speed CMOS inverters and a MOSFET power switching unit. The first-stage high-speed CMOS inverter is used to repair the edge distortion of the PWM signal after isolation transmission, and the second-stage high-speed CMOS inverter is used to improve the driving capability of the PWM signal. After two inversions, the original phase of the PWM signal is restored. The MOSFET power switching unit uses an N-channel MOSFET to build a common-source switching circuit, which converts the low-voltage logic PWM signal into a power-level PWM signal with an amplitude matching the fan supply voltage, directly adapting to the level requirements of the fan speed control pin.

9. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: The mode switching module includes a dual-channel input analog switch. The first input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM shaping drive module, the second input terminal of the dual-channel input analog switch is connected to the output terminal of the PWM to analog module, and the output terminal of the dual-channel input analog switch is connected to the speed control pin of the fan to be controlled. The main control unit controls the output mode of the dual-channel input analog switch through digital control signals, realizing the mutual exclusion switching between PWM speed regulation mode and analog speed regulation mode.

10. The fan speed control signal adaptive output, real-time calibration, and fault diagnosis system according to claim 1, characterized in that: Both the first PWM frequency measurement module and the second PWM frequency measurement module include a pulse shaping circuit and a main control hardware timer unit; The pulse shaping circuit is used to limit and shape the fan speed feedback pulse and the output PWM signal. The main control hardware timer unit is used to capture the frequency and duty cycle of the pulse signal, and calculate the actual fan speed and the actual duty cycle of the output PWM.

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