Brushless direct current motor driving system with PID (Proportion Integration Differentiation) control

Abstract

The utility model provides a brushless direct current motor driving system with PID control. A motor comprises a PID speed ring, a PID current ring and a three-phase brushless direct current motor. The PID speed ring comprises an MCU, a driving chip and an AD converter; the PI D current loop comprises an MCU, a driving chip and a current sensor; the MCU sends control information to the driving chip through an SPI interface and generates a PWM signal with an adjustable duty ratio to the driving chip at the same time, and the driving chip drives the three-phase brushless direct current motor to operate through the three-phase bridge; the AD converter detects the back electromotive force of the three-phase brushless direct current motor in real time to achieve the rotating speed, and signals are fed back to the MCU to achieve rotating speed adjustment. The current sensor detects current information of the three-phase bridge, and a signal is fed back to the MCU to limit the maximum current of the motor; according to the utility model, a speed loop and a current loop are combined, so that the motor can stably operate within a set safe current, and the motor is enabled to respond quickly due to the high-performance single-chip microcomputer processor.

Description

Technical Field

[0001] The utility model relates to the technical field of brushless DC motors, in particular to a brushless DC motor drive system containing PID control. Background Art

[0002] Brushless DC motors (BLDC) have been widely used in aerospace models, power tools, home appliances, automotive electronics and other fields due to their high efficiency, high output power, low noise, long life and high reliability. The control of BLDC motors usually relies on electronic devices to adjust the current and phase of the motor. However, existing brushless motor drivers are usually optimized for specific application scenarios and load conditions during design, which limits their performance under varying operating conditions.

[0003] In addition, the traditional speed loop can only keep the motor running at a constant speed. When encountering greater resistance, the motor operating current will rise rapidly. When the current is too large, the circuit board will be at risk of burning out. Utility Model Content

[0004] The utility model aims to provide a brushless DC motor that realizes dual control of speed and current to adapt to various application scenarios.

[0005] In order to achieve the above object, the utility model proposes a brushless DC motor drive system with PID control, including a PID speed loop, a PID current loop and a three-phase brushless DC motor;

[0006] The PID speed loop includes MCU, driver chip and speed sensor; the PID current loop includes MCU, driver chip and current sensor;

[0007] The MCU sends control information to the driver chip through the SPI interface, and generates a PWM signal with adjustable duty cycle to the driver chip. The driver chip drives the three-phase brushless DC motor through a three-phase bridge.

[0008] The speed sensor detects the rotation speed of the three-phase brushless DC motor in real time, and the signal is fed back to the MCU; the current sensor detects the current information of the three-phase bridge, and the signal is fed back to the MCU.

[0009] Furthermore, the speed sensor is an AD converter for measuring the back electromotive force of the three-phase brushless DC motor when it is running.

[0010] Furthermore, it also includes a control button, which is communicatively connected with the MCU.

[0011] Furthermore, the control chip generates three complementary PWM signals to the three-phase bridge to control the speed of the motor body.

[0012] Furthermore, signal transmission is achieved between the MCU and the control chip through the SPI interface, PWM interface and IO interface.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] 1. When the motor of the utility model is under heavy load, the maximum output current is limited due to the existence of the current loop, and the motor will not overheat or stall.

[0015] 2. This utility model is based on the application of high-performance single-chip processor, combining the speed loop and the current loop. During the startup process, it is not a traditional constant frequency or linear open loop startup. Instead, it will detect the starting load with a small pulse, combined with a current limiting strategy, to ensure that the motor starts with maximum efficiency.

[0016] 3. The BLDC PID driving method of the utility model can adapt to the long-term wear of the motor through a closed-loop circuit structure and reduce maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural block diagram of a brushless DC motor in an embodiment of the utility model;

[0018] Figure 2 This is a schematic diagram of the control structure of the three-phase bridge circuit in the embodiment of the utility model;

[0019] Figure 3 This is a six-step commutation timing diagram in an embodiment of the utility model;

[0020] Figure 4 It is a current trend diagram of the three-phase bridge winding in the embodiment of the utility model;

[0021] Figure 5 It is a timing diagram of the back electromotive force in the embodiment of the utility model;

[0022] Figure 6 This is a block diagram of a PID loop in an embodiment of the utility model;

[0023] Figure 7 This is a schematic diagram of the PID closed-loop control principle in an embodiment of the present utility model.

[0024] Figure 8 This is a circuit diagram of a driver chip in an embodiment of the utility model;

[0025] Fig. 9 1 is a circuit diagram of a controller in an embodiment of the present utility model. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the utility model clearer, the technical solution of the utility model will be further described below.

[0027] like Figure 1 As shown, the utility model proposes a brushless DC motor, including a control button, an MCU, a control chip, a three-phase bridge, a motor body, a speed sensor and a current sensor; the control button is communicatively connected to the MCU, the MCU is signal-connected to the control chip, the control chip generates three complementary PWM signals to the three-phase bridge, and controls the rotation speed of the motor body; the speed sensor detects the rotation speed of the motor body and feeds it back to the MCU, and the current sensor detects the current signal of the three-phase bridge and transmits it to the MCU.

[0028] In this embodiment, STM8S105K6T6 is selected as the main controller. The MCU has the following main features:

[0029] ·16MHz advanced STM8 core, Harvard architecture and 3-stage pipeline.

[0030] Up to 32Kbyte Flash and 2Kbyte RAM.

[0031] Advanced control timer: 16bit. 4 capture channels, 3 output comparison channels. Support dead time.

[0032] · SPI interface up to 8Mbit / s.

[0033] Up to 10 10-bit, ±1LSB ADC channels, supporting scan mode.

[0034] The operating circuit of the controller is as follows Fig. 9 shown.

[0035] The driver chip uses the A4960 chip produced by Allegro, which is a three-phase sensorless brushless DC (BLDC) motor controller that can be used with an external N-channel power MOSFET. The motor is driven by blocking commutation (trapezoidal commutation), which does not require a separate position sensor and can be determined by monitoring the motor's back electromotive force. The programmable motor startup design allows the A4960 to be adjusted for a large number of motor and load combinations. Integrated diagnostics can indicate undervoltage, overtemperature, and power bridge faults, and can be configured to protect the power MOSFET in most short-circuit conditions; the operating circuit of the driver chip is as follows: Figure 8 shown.

[0036] The control button is two Hall sensors, one for controlling the motor speed and the other for controlling the motor rotation direction. After the MCU reads the information from the Hall sensor, it sends the control information to the driver chip through the SPI interface, and generates a PWM signal with adjustable duty cycle to the driver chip to control the motor speed. The driver chip generates 3 complementary PWM signals to the three-phase bridge circuit, such as Figure 2shown.

[0037] like Figure 3 As shown, each time the motor commutates, one winding is connected to the positive pole of the control power supply (current enters the winding), the second winding is connected to the negative pole (current flows out of it), and the third winding is in a de-energized state, such as Figure 3 The torque is generated by the interaction between the magnetic field generated by the stator coil and the permanent magnet. Ideally, the torque peaks when the two magnetic fields are orthogonal and is weakest when the two magnetic fields are parallel. To keep the motor turning, the magnetic field generated by the stator windings should constantly change position because the rotor rotates in a direction parallel to the stator magnetic field. "Six-step commutation" defines the order in which the windings are energized.

[0038] When the BLDC motor rotates, each winding generates a voltage called back EMF (back EMF), such as Figure 5 As shown, according to Lenz's law, its direction is opposite to the main voltage supplied to the winding. The polarity of this back EMF is opposite to the excitation voltage. Based on this principle, we can implement speed sensor commutation detection. For a BLDC motor, taking a typical single-pole pair as an example, the motor rotates one circle for every 6 commutations. First, commutation is performed according to the set frequency to make the motor rotate. This process is called "open-loop start". When the motor rotates, a back EMF is generated. The number of steps the motor is currently running can be known based on the back EMF, and then commutation is performed to keep the motor running continuously. This process is called "closed-loop operation". Through the analysis of the operating principle of the motor, it can be known that as long as the commutation frequency is measured, the speed of the motor can be known.

[0039] The rotor position information is determined by detecting the back electromotive force signal. After obtaining the motor rotor position signal, the motor movement can be realized according to the six-step commutation principle.

[0040] like Figure 6 As shown, based on the above-mentioned brushless DC motor, the utility model proposes a brushless DC motor drive system with PID control, including a PID speed loop, a PID current loop and a three-phase brushless DC motor; the PID speed loop includes an MCU, a driver chip and a speed sensor; the PID current loop includes an MCU, a driver chip and a current sensor; the MCU sends control information to the driver chip through an SPI interface, and generates a PWM signal with adjustable duty cycle to the driver chip to control the speed of the three-phase brushless DC motor; the speed sensor detects the speed of the three-phase brushless DC motor and feeds back to the MCU; the current sensor detects the current information of the three-phase bridge and feeds back to the MCU. This system combines the advantages of common PID control and combines the current loop and the speed loop together. At the same time, the design of an external driver chip is adopted, which can realize the stable and rapid response of the high-speed operation of the three-phase brushless sensorless motor.

[0041] like Figure 7 As shown, the control method of the above PID control system is:

[0042] Step 1: Initialize software information;

[0043] Step 2: Get whether the speed reference value set by the external setting is greater than the threshold;

[0044] Step 3: If it is greater than the threshold, write the parameters to the driver chip;

[0045] Step 4: The driver chip drives the motor to operate based on the parameter settings;

[0046] Step 5: Run the speed loop and current loop;

[0047] The speed loop detects the back electromotive force of the motor based on the AD converter, and then measures the commutation frequency to obtain the motor speed; the speed loop feeds back the speed information detected by the AD converter to the MCU, and adjusts the speed to be consistent with the set speed through the driver chip.

[0048] The current loop feeds back the current information detected by the current sensor to the MCU, and limits the maximum current of the motor through the driver chip; the maximum current is limited by reducing the speed.

[0049] Step 6: Detect whether the speed reference value V1 set externally is greater than a threshold value;

[0050] Step 7: If it is less than the threshold, the motor executes the command and stops running; if it is greater than the threshold, the motor continues to run according to the set parameters.

[0051] The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, may make any equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which shall be deemed as the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A brushless DC motor drive system with PID control, characterized in that: Including PID speed loop, PID current loop and three-phase brushless DC motor; The PID speed loop includes an MCU, a driver chip and a speed sensor; the PID current loop includes the MCU, the driver chip and a current sensor; The MCU sends control information to the driver chip through the SPI interface, and generates a PWM signal with adjustable duty cycle to the driver chip, and the driver chip drives the three-phase brushless DC motor to operate through a three-phase bridge; The speed sensor detects the rotation speed of the three-phase brushless DC motor in real time, and the signal is fed back to the MCU; the current sensor detects the current information of the three-phase bridge, and the signal is fed back to the MCU.

2. The brushless DC motor drive system with PID control according to claim 1, characterized in that: The speed sensor is an AD converter for measuring the back electromotive force when the three-phase brushless DC motor is running.

3. The brushless DC motor drive system with PID control according to claim 1, characterized in that: It also includes a control button, which is communicatively connected with the MCU.

4. The brushless DC motor drive system with PID control according to claim 1, characterized in that: The driving chip generates three complementary PWM signals to the three-phase bridge to control the speed of the motor.

5. The brushless DC motor drive system with PID control according to claim 1, characterized in that: Signal transmission is achieved between the MCU and the driver chip via the SPI interface, PWM interface and IO interface.

Images