FPGA-based three-phase DC brushless motor frequency conversion control circuit for offshore fishing equipment

　　Project Name: Circuit Design of Ocean Fishing Device Based on FPGA for Three-Phase DC Brushless Motor Frequency Control

　　Main content of the project: In the actual operation process, the offshore fishing device should have the function of automatically adjusting to the acceleration or deceleration state according to the weight of the squid, and should have the ability to measure the length of the fishing line to realize the function of automatically stopping the fishing machine when the fishing line is fully rolled up.

　　This project uses FPGA to control the three-phase DC motor. The EAB can be used to form a control waveform data table required to store the current of each phase of the motor. The digital comparator designed using FPGA can synchronously generate multiple PWM current waveforms to flexibly control the three-phase DC motor, thereby meeting the needs of the actual operation of the deep-sea fishing equipment.

　　Innovation: Using XLINX's FPGA, power device intelligent module IPM PS21865 and Hall sensor position detection, the brushless DC motor drive and speed regulation are realized. The brushless DC motor BLDC uses an electronic commutator to replace the mechanical commutation device of the traditional DC motor, overcoming the noise, sparks, electromagnetic interference, short life and other drawbacks caused by the brush and commutator. The brushless DC motor has the advantages of simple structure, reliable operation and convenient maintenance of AC motors. However, it is difficult to achieve the same control effect with traditional single-chip microcomputers and DSP controls.

　　Practicality: Using FPGA to realize multi-channel PWM control, without the need for external D/A converter, greatly simplifies the peripheral control circuit, makes the control method simple, has high control accuracy and good control effect; the controller adopts the general microcontroller AT89S51, which has mature technology and low cost.

　　Achievability:

　　The FPGA module design obtains the stored PWM waveform data by querying the ROM, and then generates the corresponding PWM waveform output through the digital comparator. After receiving the command sent by the controller AT89S51 module, the FPGA module obtains different PWM waveform data by controlling the address counter, and can output the control signal of the rotation direction, rotation speed, and working/stop status of the three-phase DC motor.

　　The IPM module amplifies the control signal output by the FPGA module to achieve the control of the speed of the three-phase DC motor. At the same time, the IPM module will also return the overload protection and error protection signals of the three-phase DC motor to the controller AT89S51 module. After receiving the overload protection and error protection signals, the controller module will send a stop command to the FPGA module. The FPGA module stops the operation of the three-phase DC motor according to the command, thereby protecting the motor.

　　Project Implementation Plan

　　Basic structure diagram of the solution

　　Description of the program

　　At present, most of the power control of ocean fishing devices equipped by ocean fishing vessels still adopts the previous steady output mode, that is, the signal of the power control motor is stable to achieve uniform speed control of the fishing line device. Many problems are exposed in the actual application process. The traditional control method cannot automatically respond to some special situations, such as the sudden increase in the number of fish caught, causing the fishing machine to overload, or the fishing device to be unloaded due to shedding, and the fishing line device has been recovered. The motor cannot stop automatically. At this time, it is impossible to control the power output of the motor in time, which is very likely to cause accidents. Therefore, the problem of motor frequency conversion and control needs to be solved in time. Our team members plan to use FPGA technology to design a circuit for ocean fishing devices with variable frequency control of three-phase DC brushless motors. In order to achieve flexible and intelligent control of the fishing line device to deal with special situations.

　　Brushless DC Motor Control Principle

　　The stator winding of the motor is mostly made into a three-phase symmetrical star connection, which is very similar to a three-phase asynchronous motor. The rotor of the motor is attached with a magnetized permanent magnet. In order to detect the polarity of the motor rotor, a position sensor is installed in the motor. The driver is composed of power electronic devices and integrated circuits, etc. Its functions are: receiving the start, stop, and brake signals of the motor to control the start, stop, and brake of the motor; receiving the position sensor signal and the forward and reverse signals to control the on and off of each power tube of the inverter bridge to generate continuous torque; receiving the speed command and speed feedback signal to control and adjust the speed; providing protection and display, etc. The control principle diagram of the brushless DC motor is shown in Figure 3-2.

　　The main circuit is a typical voltage-type AC-DC-AC circuit, and the inverter provides a symmetrical alternating rectangular wave of equal amplitude and frequency 5-24KHz modulation wave. The permanent magnet NS is alternately exchanged, so that the position sensor generates H3, H2, and H1 square waves with a phase difference of 120°, thereby generating an effective six-state encoding signal: 010, 011, 001, 101, 100, 110, and through the logic component processing, V6-V1 conduction, V5-V6 conduction, V4-V5 conduction, V3-V4 conduction, V2-V3 conduction, V1-V2 conduction are generated, that is, the DC bus voltage is sequentially added to U->V, W->V, W->U, V->U, V->W, U->W, so that every time the rotor rotates through a pair of NS poles, the power tubes of V1, V2, V3, V4, V5, and V6 are sequentially turned on according to the fixed combination of six states. In each state, only two-phase windings are energized, and the state is changed one by one. The axis of the magnetic field generated by the stator winding rotates 60° electrical angle in space, and the rotor follows the stator magnetic field to rotate at a spatial position equivalent to 60° electrical angle. The rotor is in the new position, causing the position sensors U, V, and W to generate a new set of codes as agreed. The new codes change the conduction combination of the power tube, causing the axis of the magnetic field generated by the stator winding to advance another 60° electrical angle. This cycle continues, and the brushless DC motor will generate continuous torque and drag the load for continuous rotation.

　　This solution uses a 120-degree square wave algorithm to drive the built-in IGBT of the IPM to drive the DC brushless motor. The distribution of IGBT signals must be closely related to the position of the motor. The position signal fed back from the Hall sensor of the BLDC is encoded into six states: 010, 011, 001, 101, 100 and 110, so the IGBT drive signal can be distributed according to these six position state information. Here we prefer to use the upper bridge arm of the IGBT to distribute PWM signals, and the lower bridge arm to distribute high and low level driving methods, so the terminal voltage applied to the DC brushless motor can be changed by changing the duty cycle of the upper bridge arm PWM. The relationship between signal distribution and position is shown in Figure 3-3.

　　Among them: V1, V2, V3, V4, V5 and V6 represent the three-phase full-controlled bridge circuit composed of IGBT. The three power tubes V1, V3 and V5 of the upper bridge and the three power tubes V2, V4 and V6 of the lower bridge respectively control the flow direction of the three-phase DC power of U, V and W, as shown in Figure 1-1. H1, H2 and H3 are the three signal output lines of the Hall sensor.

　　If the relationship between the forward position signal and the drive signal is as shown in Figure 2: 010 (H3 H2 H1) V6-V1, 011 (H3 H2 H1) V5-V6, 001 (H3 H2 H1) V4-V5, 101 (H3 H2 H1) V3-V4, 100 (H3 H2 H1) V2-V3, 110 (H3 H2 H1) V1-V2, then we can also give the commutation relationship of the drive signal during reverse rotation based on the position signal. That is: 001 (H3 H2 H1) V1-V2, 011 (H3 H2 H1) V2-V3, 010 (H3 H2 H1) V3-V4, 110 (H3 H2 H1) V4-V5, 100 (H3 H2 H1) V5-V6, 101 (H3 H2 H1) V6-V1. The phase sequence of the specific motor must be made clear. If the commutation is incorrect or improper, the DC brushless motor will vibrate left and right and not rotate at all, or the current will be very large and the current waveform will be incorrect.

　　The on/off of each power tube is controlled by the above control signal, so that the current flows into the three-phase coils U, V, and W in sequence, and a rotating magnetic field is generated inside the DC brushless motor, as shown in Figure 3-4, which points out the relationship between the voltage and current direction of each phase under the action of the control signal.

　　Add PWM to the signal of the control power component and adjust the duty cycle of PWM, that is, the Duty of the output PWM, so as to adjust the terminal voltage of the input motor and control the speed of the DC brushless motor. There are four ways to add the control signal PWM: upper phase PWM, lower phase PWM, first half PWM and second half PWM, as shown in Figure 3-5.

　　FPGA modulation PWM waveform principle

　　It is planned to use FPGA to control three-phase DC motor. The EAB can be used to form a control waveform data table for storing the current of each phase of the motor, and the digital comparator designed by FPGA can synchronously generate multiple PWM current waveforms to flexibly control the three-phase DC motor. Using FPGA to realize multi-channel PWM control, there is no need for an external D/A converter, which greatly simplifies the peripheral control circuit, makes the control method simple, and has high control accuracy and good control effect. It is difficult to achieve the same control effect using a single-chip microcomputer and a DSP.

　　The FPGA module design is composed of PWM counter, waveform ROM address counter, PWM waveform ROM memory, comparator and other modules. Among them, the PWM counter counts up under the action of the pulse width clock to generate a periodic sawtooth wave with a step-shaped rise, and is loaded to one end of each digital comparator at the same time; the data output by the PWM waveform ROM is loaded to the other end of each digital comparator. When the count value of the PWM counter is less than the output value of the waveform ROM, the comparator outputs a low level; when the count value of the PWM counter is greater than the output value of the waveform ROM, the comparator outputs a high level. In this way, a periodic PWM waveform can be output. According to the requirements of the three-phase DC motor for the current waveform, the values ​​corresponding to the subdivided current waveform at each moment are stored in the waveform ROM, and the address of the waveform ROM is generated by the address counter. By controlling the address counter, the rotation direction, rotation speed, and working/stop state of the three-phase DC motor can be changed.