A brushless fan PAM controller and method based on a single-phase bridge phase-controlled rectifier

Abstract

The application belongs to the technical field of brushless fan control, and specifically provides a brushless fan PAM controller and method based on a single-phase bridge phase-controlled rectifier, which separates the speed control and the commutation control, the speed control part uses a single-phase bridge phase-controlled rectifier, and the commutation control part uses a sensorless control scheme based on a three-phase inverter bridge arm structure. Specifically, the single-phase bridge phase-controlled rectifier part converts single-phase alternating current input into direct current output, adjusts the conduction angle of a thyristor to realize current closed loop, and then realizes brushless fan speed closed loop. In the case of single-phase alternating current input power supply, the single-phase bridge phase-controlled rectifier part can replace the two components of a rectifier and a DC / DC converter in the traditional structure, saves the cost, reduces the complexity of the circuit structure, improves the efficiency and reliability, and realizes sensorless commutation control of the brushless fan through a motor line voltage sampling circuit, a driving circuit and a three-phase bridge arm inverter circuit in the commutation control part, and solves the delay commutation problem of the traditional back electromotive force method.

Description

Technical Field

[0001] This invention relates to the field of brushless fan control technology, and more specifically, to a brushless fan PAM controller and method based on a single-phase bridge phase-controlled rectifier. Background Technology

[0002] With the advancement of modern technology, brushless fans have been widely used in industries such as manufacturing, home appliances, shipbuilding, aerospace, and energy. In the industrial sector, brushless fans are used in fuel cell centrifugal air compressors, turbochargers, and industrial blowers. The brushless fans used in fuel cells can reach speeds of up to 100,000 RPM, delivering a large volume of clean air to the fuel cell system, providing sufficient oxygen for the fuel cell stack reaction and thus improving fuel cell efficiency. In the home appliance sector, high-speed brushless fans are widely used in hair dryers, vacuum cleaners, and air conditioners. High-speed vacuum cleaners can quickly pick up dust from the ground. Dyson hair dryers, with speeds up to 110,000 RPM, provide powerful airflow for quickly drying hair. The application of high-speed brushless fans in home appliances has significantly improved the user experience and comfort, and more and more users are choosing home appliances with high-speed brushless fans.

[0003] The electromagnetic torque of a brushless fan is generated by the interaction between the current in the stator windings and the rotor magnetic field.

[0004]

[0005] In the formula T em ω is the electromagnetic torque; ω is the mechanical speed of the motor.

[0006] It is evident that the magnitude of the electromagnetic torque is directly proportional to the current amplitude; therefore, controlling the output current amplitude controls the electromagnetic torque of the brushless fan. The relationship between the electromagnetic torque, load torque, and speed of the brushless fan can be described using the mechanical motion equations of an electric motor.

[0007]

[0008] In the formula, T L B is the load torque; J is the damping coefficient; and J is the moment of inertia.

[0009] For fan-type loads, the load torque is proportional to the square of the rotational speed, that is:

[0010] T L =Cω 2

[0011] In the formula, C is a constant, which depends on the load. When the brushless fan speed reaches a stable value, the electromagnetic torque T... em With load torque TL Since they are equal, it can be seen that controlling the amplitude of the output current can control the speed of the brushless fan.

[0012] Traditional low- and medium-speed brushless fans are typically controlled using PWM modulation. This involves using PWM control of the switching transistors within a three-phase bridge inverter circuit to simultaneously control the motor's speed and commutation. However, due to the lower inductance values ​​in high-speed brushless fans, PWM modulation generates more harmonic components, increasing motor torque ripple and resulting in less stable operation. Because of the smaller inductance values ​​in high-speed brushless fans, PAM control is more suitable. Figure 2 As shown, motor speed control and commutation control are separated. In the PAM control method, the first stage is a current source, which controls the motor speed by controlling the amplitude of the output current. The second stage is a three-phase inverter circuit, which is responsible for the motor's commutation control. However, when powered by AC from the grid, traditional PAM-based motor controllers require a three-stage structure of rectification, DC / DC conversion, and three-phase inverter bridge arms. This leads to problems such as increased controller cost, reduced efficiency, and reduced reliability, necessitating improvements to the traditional PAM circuit structure.

[0013] The control strategies for brushless fans can be divided into two types: sensor-based control and sensorless control. Sensor-based control involves installing position sensors, such as Hall effect sensors, inside the motor shaft to detect the rotor's position and calculate the rotor speed and commutation timing based on the information obtained. However, installing position sensors in high-speed brushless fans significantly reduces the reliability and stability of motor operation due to factors such as high speed, high frequency, rapid temperature rise, electromagnetic radiation, and high temperatures.

[0014] All of these factors can potentially cause the position sensor to malfunction. Sensorless control schemes overcome many of the shortcomings of position sensor-based control schemes. The following are some methods for obtaining the motor rotor position using back electromotive force:

[0015] Terminal voltage method: This method detects the terminal voltage of the unconducted phase and obtains the motor rotor position information based on the terminal voltage crossing zero. Typically, the switching state of the MOSFET is switched when the terminal voltage crosses zero by 30°. The disadvantage is that the terminal voltage contains high-order harmonic noise, and the low-pass filter used to remove this noise causes a phase delay. This phase delay changes with speed, affecting the accuracy of the switching.

[0016] Third harmonic method: This method obtains the rotor position information of the motor based on the third harmonic component of the back electromotive force. Typically, the switching state of the MOSFET is switched when the third harmonic component crosses zero. The third harmonic method has high accuracy but is susceptible to noise interference.

[0017] Back EMF integration method: Position information is extracted by integrating the back EMF of the unconducted phase.

[0018] Linear back EMF method: The commutation signal is obtained by detecting the line back EMF. It can still be used at low speeds, but the phase delay is relatively large.

[0019] In sensorless control schemes for brushless fans, the method of obtaining the motor rotor position through back electromotive force is the most commonly used. However, the phase delay caused by delayed commutation and low-pass filter will lead to a decrease in the operating stability of high-speed brushless fans. Summary of the Invention

[0020] This invention addresses the technical problem in the prior art where delay in commutation and phase delay caused by low-pass filters lead to a decrease in the operational stability of high-speed brushless fans when obtaining the rotor position of a motor through back electromotive force.

[0021] This invention provides a brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier, including a single-phase bridge phase-controlled rectifier and a commutation control circuit for commutation control of the brushless fan, wherein the output terminal of the single-phase bridge phase-controlled rectifier is connected to the input terminal of the commutation control circuit.

[0022] The single-phase bridge phase-controlled rectifier adopts a current loop control mode, which adjusts the output current and controls the rotation speed by controlling the conduction angle of the thyristors.

[0023] The commutation control circuit uses rotor position feedback to activate the corresponding windings for commutation control.

[0024] Preferably, the single-phase bridge phase-controlled rectifier includes four thyristors, two in a group, with each group having a phase difference of 180 degrees. Closed-loop control of the output current is achieved by controlling the conduction angle of each group.

[0025] Preferably, a freewheeling diode and a voltage-regulating capacitor are connected in parallel at the output terminal of the single-phase bridge phase-controlled rectifier.

[0026] Preferably, the commutation control circuit includes a three-phase inverter bridge arm circuit, a motor line voltage sampling circuit, and a drive circuit;

[0027] The motor line voltage sampling circuit is used to obtain the rotor position in real time. Based on the expected value of the rotor position and the actual value of the rotor position feedback, the circuit drives the six switching transistors of the three-phase bridge arm to turn on and off.

[0028] Preferably, the three-phase inverter bridge arm circuit includes six MOSFETs, with two MOSFETs forming a group to form a three-phase bridge arm. Inversion is achieved by controlling the six MOSFETs to be turned on or off within one cycle.

[0029] Preferably, the motor line voltage sampling circuit is used to scale and filter the acquired motor line voltage through two operational amplifiers; then, the three motor line voltages are compared pairwise by a hardware comparator to obtain the commutation point, thereby realizing the commutation control of the motor.

[0030] Preferably, the drive circuit is used to obtain the commutation point by comparing the line voltages of each motor, and to drive the six MOS transistors of the three-phase inverter bridge arm through a bootstrap circuit.

[0031] Preferably, each phase of the three-phase inverter bridge arm has two MOSFETs, one upper and one lower. The source S of the lower MOSFET is grounded, and the source S of the upper MOSFET is floating. The output is sent to the gate of the MOSFET through a bootstrap circuit to drive the three-phase inverter bridge arm.

[0032] Preferably, the single-phase bridge phase-controlled rectifier includes two PI controllers and a phase-controlled rectifier bridge, and the closed-loop control of the motor speed is achieved by controlling the conduction angle of the thyristors in the rectifier bridge;

[0033] The commutation control circuit adopts a sensorless control scheme based on motor line voltage. The motor line voltage is sampled by a sampling circuit to obtain a commutation signal, which is then controlled by a drive circuit to control the three-phase inverter bridge arm to achieve commutation control.

[0034] This invention also provides a PAM control method for a brushless fan based on a single-phase bridge phase-controlled rectifier. This control method is used to control the PAM controller of a brushless fan based on a single-phase bridge phase-controlled rectifier, and includes the following steps:

[0035] S1, the strong drag stage, controls the motor bus current to stabilize at the set value, and at the same time controls the six switching transistors of the three-phase inverter bridge arm to switch on and off periodically in sequence, thereby accelerating the frequency of switching transistors and completing the motor start-up.

[0036] S2, autonomous commutation stage: by sampling the motor line voltage, the switching transistors of the three-phase bridge arm are turned on according to the comparison result obtained by the hardware comparator, and the bus current is controlled to drive the motor to accelerate.

[0037] S3, the closed-loop speed control stage, completes the motor speed control based on the speed setpoint and the actual speed of the motor.

[0038] Beneficial effects: The present invention provides a brushless fan PAM controller and method based on a single-phase bridge phase-controlled rectifier. The single-phase AC input is converted into DC output by the single-phase bridge phase-controlled rectifier. The current closed loop is achieved by adjusting the conduction angle of the thyristors, thereby realizing the brushless fan speed closed loop. Under AC input power supply, the use of a single-phase bridge phase-controlled rectifier saves costs, reduces the complexity of the circuit structure, and improves efficiency and reliability.

[0039] The commutation control section adopts a sensorless control algorithm, which realizes the commutation control of the brushless fan through the motor line voltage sampling circuit, drive circuit and three-phase bridge arm inverter circuit, thus solving the problem of delayed commutation in the traditional back EMF method.

[0040] The controller separates speed control and commutation control. The speed control section uses a single-phase bridge phase-controlled rectifier, while the commutation control section uses a sensorless control scheme. In order to adapt to the characteristics of high-speed / ultra-high-speed brushless fans such as small inductance, difficult start-up, and high speed, a three-stage start-up closed-loop control strategy is used. A sensorless control scheme for high-speed brushless fans with no commutation delay based on a single-phase bridge phase-controlled rectifier is proposed. Attached Figure Description

[0041] Figure 1 A flowchart of a brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier is provided for this invention.

[0042] Figure 2 The background diagram shows the conventional PAM structure circuit of a brushless fan in the prior art of this invention.

[0043] Figure 3 A block diagram of a sensorless control program based on motor line voltage-based delay-free commutation provided by the present invention;

[0044] Figure 4a The input voltage waveform diagram provided for this invention;

[0045] Figure 4b The output average voltage waveform diagram provided for this invention;

[0046] Figure 4c The output average current waveform diagram provided for this invention;

[0047] Figure 4d The waveform diagram of the thyristor conduction time provided by the present invention;

[0048] Figure 5 The schematic diagram of the motor line voltage sampling circuit provided by the present invention;

[0049] Figure 6a The motor line voltage diagram collected by this invention;

[0050] Figure 6b The waveform obtained after passing through a differential amplifier is provided by the present invention.

[0051] Figure 6c The waveform obtained after passing through a low-pass filter is provided by the present invention.

[0052] Figure 7 A flowchart of the motor operation procedure provided by the present invention. Detailed Implementation

[0053] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0054] Figure 1 This invention provides a brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier, comprising a single-phase bridge phase-controlled rectifier and a commutation control circuit for commutation control of the brushless fan. The output terminal of the single-phase bridge phase-controlled rectifier is connected to the input terminal of the commutation control circuit. The single-phase bridge phase-controlled rectifier adopts a current loop control mode, and adjusts the output current by controlling the conduction angle of the thyristors to control the speed. The commutation control circuit uses rotor position feedback to correspondingly activate the corresponding windings for commutation control.

[0055] The commutation control circuit mainly includes a three-phase inverter bridge arm circuit, a motor line voltage sampling circuit, and a three-phase inverter bridge arm drive circuit. Based on the results of the motor line voltage sampling circuit, and according to the expected and actual values, the commutation control circuit drives the six switching transistors of the three-phase bridge arm to turn on and off through the drive circuit, ultimately achieving commutation control of the motor.

[0056] With this scheme, speed regulation is achieved by the front stage, and the three-phase bridge arm of the rear stage does not need to generate high-frequency PWM. Therefore, it has lower switching losses and lower winding current harmonics, making it more suitable for high-speed / ultra-high-speed brushless fan applications.

[0057] The controller's control process includes: a sensorless control scheme based on motor line voltage and a start-up control process, which includes three stages: a strong drag stage, an autonomous commutation stage, and a speed closed-loop stage.

[0058] The initial startup phase involves controlling the current to periodically turn on the switching transistor to drive the motor. The autonomous commutation phase utilizes the sensorless control scheme described in this invention to complete the commutation operation, during which the control current drives the motor to accelerate. The speed closed-loop phase involves closed-loop control of the motor's speed and commutation based on the set speed value. This three-stage startup control process refines the functionality, adapting to the characteristics of high-speed / ultra-high-speed brushless fans, such as low inductance, difficult startup, and high speed, thus facilitating smooth motor startup and reliable operation.

[0059] Preferred solutions, such as Figure 1 As shown, a single-phase bridge phase-controlled rectifier rectifies alternating current (AC) to direct current (DC). For a 50Hz single-phase AC input, this rectifier employs full-bridge phase control. Four thyristors, VT1 to VT4, are used in this rectifier, arranged in pairs, with each pair separated by a 180-degree phase difference. Closed-loop control of the output current is achieved by controlling the conduction angle of each pair.

[0060] In the preferred embodiment, in addition to the four thyristors serving as the rectifier bridge, a freewheeling diode D1 is connected in parallel at the output of the single-phase bridge phase-controlled rectifier. This allows for inductor freewheeling when all thyristors are turned off, ensuring continuous current flow. A voltage-regulating capacitor C is also used at the output of the rectifier circuit. f It plays a role in stabilizing voltage, which is beneficial for the subsequent three-phase bridge arm inverter circuit to control the motor.

[0061] Specifically, the 50Hz AC power from household use is directly rectified into the required DC power using a single-phase bridge phase-controlled rectifier circuit constructed with thyristors, inductors, and capacitors. Thyristors VT1 and VT4 form one group, and thyristors VT2 and VT3 form another group, with the two groups separated by 180 degrees. By controlling the conduction angle, the output DC power of the bridge rectifier circuit can be controlled, thereby achieving control of the bus current, i.e., closed-loop control of the motor speed. The inductor L in the single-phase bridge phase-controlled rectifier circuit... f It serves as an energy storage device, maintaining a stable output current. The capacitor C... f Diode D1 acts as a voltage regulator, while diode D1 acts as a freewheeling current generator, allowing current to flow between the inductor L and the voltage regulator even when the bridge arm is off. f and capacitor C f This forms a loop. Unlike the quasi-current source section in the traditional PAM structure, the single-phase bridge phase-controlled rectifier module in this invention has both rectification and amplitude modulation functions.

[0062] In the preferred embodiment, the commutation control circuit mainly includes a three-phase inverter bridge arm circuit, a motor line voltage sampling circuit, and a drive circuit for the three-phase inverter bridge arm. Based on the results of the motor line voltage sampling circuit (i.e., the actual rotor position feedback value), and according to the desired rotor position and the actual rotor position feedback value, the commutation control circuit drives the six switching transistors of the three-phase bridge arm to turn on and off via the drive circuit, ultimately achieving commutation control of the motor.

[0063] In the preferred embodiment, the three-phase inverter bridge arm circuit uses a total of six MOSFETs, with two MOSFETs grouped together to form the three-phase bridge arm. The inverter circuit only needs to control the on / off state of these six MOSFETs within one cycle to achieve the inverter effect, eliminating the need for modulation of the motor voltage amplitude through these six switching transistors. This significantly reduces the switching frequency of the switching transistors in the three-phase inverter circuit, reduces switching losses, lowers the requirements for the switching transistors, and increases the possibility of increasing motor speed.

[0064] In the preferred embodiment, the motor line voltage sampling circuit scales and filters the acquired motor line voltages using two operational amplifiers. Then, a hardware comparator compares the three motor line voltages pairwise to determine the commutation point, thereby achieving commutation control of the motor. The low-pass filter in the motor line voltage comparison circuit acts as an integrator, filtering the waveform while delaying it by 90 degrees, which is more convenient than the traditional back-EMF commutation method and reduces commutation delay operations.

[0065] Specifically, the motor line voltage sampling circuit is as follows: Figure 5 As shown, the first operational amplifier acts as a differential amplifier, primarily amplifying or reducing the acquired signal. The second operational amplifier forms a low-pass filter, designed to remove high-order harmonic interference from the signal, resulting in a motor line voltage containing only the fundamental component. In conventional schemes, back-EMF commutation requires a 30-degree delay. In this invention, the motor line voltage sampling circuit causes a 90-degree waveform delay, requiring only a 60-degree delay to achieve commutation. For sensorless square wave control schemes, which inherently perform sequential commutation at 60-degree intervals, this commutation operation only needs to be completed at the previous commutation point, eliminating the need for further delay. The motor line voltage sampling circuit in this invention avoids delayed commutation, increasing operational reliability.

[0066] In the preferred embodiment, the drive circuit obtains the commutation point through the motor line voltage comparison circuit, and completes the driving of the six MOSFETs of the three-phase inverter bridge arm through the bootstrap circuit. The bootstrap circuit only needs to perform simple switching operations on the six MOSFETs, without the need for PWM modulation, thus reducing switching losses.

[0067] In the preferred embodiment, the drive circuit uses a bootstrap driving method. Since each phase bridge arm has two switching transistors (MOSFETs), the source (S) of the lower transistor is grounded, so applying a relatively low voltage to its gate (G) is sufficient to turn it on. However, the source (S) of the upper transistor is floating, and applying a relatively low voltage to its gate (G) is insufficient to turn it on. Therefore, a bootstrap method is used in the drive circuit, employing a bootstrap capacitor to switch the upper transistor.

[0068] In the preferred embodiment, the speed control section uses a single-phase bridge phase-controlled rectifier mainly composed of two PI controllers and a phase-controlled rectifier bridge. Closed-loop control of the motor speed is achieved by controlling the conduction angle of the thyristors in the rectifier bridge. For the commutation control section, the commutation control circuit adopts a sensorless control scheme based on the motor line voltage. The motor line voltage is sampled by a sampling circuit to obtain the commutation signal, which is then used by the drive circuit to control the three-phase inverter bridge arms to achieve commutation control.

[0069] In a specific implementation scenario:

[0070] First, single-phase alternating current must pass through a single-phase bridge phase-controlled rectifier. A bridge rectifier circuit, consisting of thyristors, inductors, and capacitors, is used. Figure 3 The phase-controlled rectifier section is shown. The input is single-phase AC power, and the AC voltage is:

[0071] u2=U2sin 50t

[0072] Input voltage waveform as follows Figure 4a As shown. With a conduction angle of α, the average rectified output voltage is:

[0073]

[0074] The output average voltage waveform is as follows Figure 4b As shown. Because the rectifier circuit in this invention has a large inductance L as its load. f This allows the output current to be nearly constant, while the load still has a relatively large resistance R. f Capacitor C f It serves to stabilize the voltage, and the average rectified output current is:

[0075] IBUS = (U d -V out ) / R f

[0076] The average voltage of the rectified output U d Substituting into the above equation, we can obtain the relationship between the rectified output average current IBUS and the conduction angle α as follows:

[0077] IBUS=(0.9U2cosα-V out ) / R f

[0078] Output average current waveform as follows Figure 4c As shown, Figure 4d The waveform shows the thyristor's conduction timing. From the waveform and the above equation, it can be seen that the average rectified output voltage U can be adjusted by changing the conduction angle α. d With the control of the conduction angle α changing from 0 to π, the average rectified output voltage U d The effective value changes from the maximum value to 0. This is due to the inductance L in the circuit. f The function of this system is to prevent sudden changes in the rectified output average current IBUS, which remains relatively stable. The effective value of the rectified output average current IBUS is determined by the rectified output average voltage U. d The effective value is determined by the conduction angle α. Therefore, controlling the conduction angle α can realize the control of the rectified output average current IBUS. At the same time, the rectified output average current IBUS is the input current of the three-phase bridge arm inverter circuit. By controlling the magnitude of the input current, the motor speed can be controlled. That is, the single-phase bridge phase-controlled rectifier circuit in this invention has both rectification and amplitude regulation functions.

[0079] Then, to complete the control of the motor, a commutation control circuit is also needed. This mainly consists of three parts: a motor line voltage sampling circuit module, a drive circuit module, and a three-phase bridge arm inverter circuit module. The motor line voltage sampling circuit module is as follows: Figure 5 As shown, terminal voltages BEMF_A and BEMF_B are obtained from the motor terminals. These are differentially amplified by operational amplifier U1 to obtain the line voltages BEMF_AB of phases A and B. Then, they are low-pass filtered by operational amplifier U2 to obtain the line voltage BEMF_AB containing only the fundamental frequency component. * Then, based on the line voltage BEMF_AB * The motor commutation point can then be obtained, eliminating the need for further delayed commutation. For example... Figure 6a The figure shows the collected motor terminal voltage values. t1, t2, t3, t4, t5, and t6 represent six commutation points within one cycle. Commutation of phases B and C is performed at point t2. Generally, the zero-crossing point of the back electromotive force is used as the commutation basis. Here, the commutation point needs to be delayed by 30 degrees. For example... Figure 6b The waveform shown is the result after passing through the first operational amplifier, i.e., the differential amplifier. Subtracting BEMF_A from BEMF_B yields BEMF_AB, at which point the waveform contains a significant number of harmonic components. Figure 6c The image shows the waveform obtained after passing through the second operational amplifier, i.e., the low-pass filter. This waveform is delayed by 90 degrees. At this point, no commutation operation is needed; only the obtained BEMF_AB needs to be adjusted. * BEMF_BC * and BEMF_CA * By performing pairwise comparisons, the reversal points can be obtained. Taking point t2 as an example, at this point BEMF_AB * From less than BEMF_CA * Change to greater than BEMF_CA * Therefore, simply turn off the lower pipe of phase B arm and turn on the lower pipe of phase C arm. Similarly, at point t3, BEMF_BC * From less than BEMF_CA * Change to greater than BEMF_CA * Then, by turning off the upper tube of phase A bridge arm and turning on the upper tube of phase B bridge arm, and so on, six switching states can be achieved to control the motor rotor to rotate one revolution.

[0080] Analyze the low-pass filter, such as Figure 5 As shown, resistors R3 and R5 are 2kΩ, resistor R4 is 100kΩ, and capacitor C1 is 100nF. Bode plot analysis yields the results shown in Table 1 below:

[0081] Table 1 Rotational speed and delay phase

[0082] motor speed angular frequency Delayed phase 1000rpm 114 rad / s 48.6 degrees 5000rpm 569rad / s 80 degrees 10000rpm 1047 rad / s 84.6 degrees 60000rpm 6283 rad / s 89.1 degrees 120000rpm 12566rad / s 89.5 degrees

[0083] The table shows that the phase delay reaches 89.1 degrees when the motor speed reaches 60,000 rpm, and 89.5 degrees when the motor speed reaches 120,000 rpm. Therefore, it can be considered that for a high-speed brushless fan, this low-pass filter is an integrator, causing a 90-degree phase delay in the motor line voltage. After passing through the low-pass filter, an ideal line voltage waveform is obtained, containing only the fundamental component with a 90-degree phase delay. The designed low-pass filter not only filters out higher harmonics but also solves the commutation delay problem.

[0084] Finally, to make the motor run as required, a program needs to be written into the controller. The program block diagram is as follows: Figure 2 As shown, the flowchart of the program execution is as follows: Figure 7 As shown. First is the forced-drive stage, where the current is already in closed-loop control, but the speed is not. Current closed-loop control is achieved by using the setpoint and actual value of the motor bus current to obtain the conduction angle α, which is then controlled by a single-phase phase-controlled rectifier circuit. Changing the current setpoint changes the motor speed. The purpose of the forced-drive stage is to start the motor; this is achieved by periodically and sequentially turning on the switches on the three-phase inverter bridge arms in the commutation control section. Next is the autonomous commutation stage, where the motor line voltage is significant, allowing for direct commutation control based on the line voltage. The goal of this stage is to rapidly increase the motor speed, quickly approaching the ultra-high speed setpoint. Finally, there is the speed closed-loop stage. The setpoint and actual value of the motor speed are used to obtain the bus current setpoint, and the actual value of the bus current is used to obtain the conduction angle α, completing the current control of the motor. Simultaneously, commutation control is performed based on the line voltage, ensuring that the commutation operation matches the motor speed, thus completing the motor speed closed-loop control.

[0085] This invention also provides a PAM control method for a brushless fan based on a single-phase bridge phase-controlled rectifier. This method controls the PAM controller of the brushless fan based on the single-phase bridge phase-controlled rectifier as described above, and includes the following steps:

[0086] S1, the strong drag stage, controls the motor bus current to stabilize at the set value, and at the same time controls the six switching transistors of the three-phase inverter bridge arm to switch on and off periodically in sequence, thereby accelerating the frequency of switching transistors and completing the motor start-up;

[0087] S2, autonomous commutation stage: by sampling the motor line voltage, the switching transistors of the three-phase bridge arm are turned on according to the comparison result obtained by the hardware comparator, and at the same time, the bus current is controlled to drive the motor to accelerate.

[0088] S3, the closed-loop speed control stage, completes the motor speed control based on the speed setpoint and the actual speed of the motor.

[0089] Beneficial effects:

[0090] 1. It can directly use household single-phase AC power without the need for additional DC power supply equipment. Compared with the traditional PAM structure controller, it saves costs, reduces complexity, and improves efficiency and reliability.

[0091] 2. The separation of speed control and commutation control is beneficial for driving high-speed brushless fans, and the single-phase bridge rectifier section realizes the dual functions of rectification and amplitude regulation;

[0092] 3. Improved the shortcomings of the sensorless control algorithm based on back EMF and solved the problem of commutation delay.

[0093] It should be noted that the descriptions of each embodiment in the above embodiments have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0094] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0095] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier, characterized in that, include: The single-phase bridge phase-controlled rectifier adopts a current loop control mode, which adjusts the output current and controls the speed by controlling the conduction angle of the thyristors. The commutation control circuit uses the rotor's position feedback to activate the corresponding windings for commutation control. The output terminal of the single-phase bridge phase-controlled rectifier is connected to the input terminal of the commutation control circuit. The commutation control circuit includes a three-phase inverter bridge arm circuit, a motor line voltage sampling circuit, and a drive circuit. The motor line voltage sampling circuit is used to obtain the rotor position in real time. Based on the expected value of the rotor position and the actual value of the rotor position feedback, the circuit drives the six switching transistors of the three-phase bridge arm to turn on and off. The motor line voltage sampling circuit is used to scale and filter the acquired motor line voltage through two operational amplifiers; then, the three motor line voltages are compared pairwise by a hardware comparator to obtain the commutation point, thereby realizing the commutation control of the motor.

2. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 1, characterized in that, The single-phase bridge phase-controlled rectifier includes four thyristors, two in a group, with each group having a phase difference of 180 degrees. Closed-loop control of the output current is achieved by controlling the conduction angle of each group.

3. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 2, characterized in that, A freewheeling diode and a voltage regulator capacitor are connected in parallel at the output terminal of the single-phase bridge phase-controlled rectifier.

4. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 1, characterized in that, The three-phase inverter bridge arm circuit includes six MOSFETs, with two MOSFETs forming a group to form a three-phase bridge arm. Inversion is achieved by controlling the six MOSFETs to turn on or off within one cycle.

5. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 1, characterized in that, The drive circuit is used to obtain the commutation point by comparing the line voltages of each motor, and to drive the six MOS transistors of the three-phase inverter bridge arm through the bootstrap circuit.

6. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 5, characterized in that, Each phase of the three-phase inverter bridge arm has two MOSFETs, one upper and one lower. The source S of the lower MOSFET is grounded, while the source S of the upper MOSFET is floating. The output is sent to the gate of the MOSFET through a bootstrap circuit to drive the three-phase inverter bridge arm.

7. The brushless fan PAM controller based on a single-phase bridge phase-controlled rectifier according to claim 1, characterized in that, The single-phase bridge phase-controlled rectifier includes two PI controllers and a phase-controlled rectifier bridge, and achieves closed-loop control of the motor speed by controlling the conduction angle of the thyristors in the rectifier bridge. The commutation control circuit adopts a sensorless solution based on motor line voltage. The motor line voltage is sampled by a sampling circuit to obtain a commutation signal, which is then controlled by a drive circuit to control the three-phase inverter bridge arm to achieve commutation control.

8. A PAM control method for a brushless fan based on a single-phase bridge phase-controlled rectifier, characterized in that, The control method is used to control the PAM controller of a brushless fan based on a single-phase bridge phase-controlled rectifier as described in any one of claims 1-7, and includes the following steps: S1, the strong drag stage, controls the motor bus current to stabilize at the set value, and at the same time controls the six switching transistors of the three-phase inverter bridge arm to switch on and off periodically in sequence, thereby accelerating the frequency of switching transistors and completing the motor start-up. S2, autonomous commutation stage: by sampling the motor line voltage, the switching transistors of the three-phase bridge arm are turned on according to the comparison result obtained by the hardware comparator, and the bus current is controlled to drive the motor to accelerate. S3, the closed-loop speed control stage, completes the motor speed control based on the speed setpoint and the actual speed of the motor.

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