0 Introduction
    Since the 1980s, the development of power electronics, computer technology and automatic control theory has created conditions for the development of AC electric drive products, making AC drives gradually have the technical performance of wide speed regulation range, high precision, fast dynamic response and good four-quadrant operation. Today, electric motors have become the most important power source and occupy an important position in production and life. The AC three-phase asynchronous motor has a dominant position among AC motors due to its simple structure, convenient manufacturing, reliable operation, low price and flexible control. With the widespread application of high-performance digital processing chips DSP, the speed regulation of three-phase asynchronous motors has entered a new stage, and its speed regulation performance is almost comparable to that of DC motors. This paper uses DSC (digital signal controller), which is an embedded controller that integrates the control function of a single-chip microcomputer (MCU) and the computing power of a digital signal processor (DSP), and is cheap.

1 System hardware design
1.1
    The mathematical model of the vector-controlled asynchronous motor in the three-phase stationary coordinate system is very complex, mainly due to its complex magnetic flux relationship. Therefore, to simplify the mathematical model, the mathematical model of the asynchronous motor must be transformed from the three-phase stationary coordinate system to the two-phase synchronous rotating coordinate system through coordinate transformation. The transformation from the three-phase stationary coordinate system (ABC coordinate system) to the two-phase stationary coordinate system (Oab coordinate system) is called Clarke transformation, and the transformation from the two-phase stationary coordinate system to the two-phase synchronous rotating coordinate system (OMT coordinate system) is called Park transformation.
    Vector control is also called field-oriented control. Through coordinate transformation, the current vector is decomposed into the excitation current component ism that generates magnetic flux and the torque current component ist that generates torque in the two-phase synchronous rotating coordinate system, and the two components are made perpendicular to each other and independent of each other, and then adjusted separately. In this way, the torque control of the AC motor is similar to that of the DC motor in terms of principle and characteristics. This is the core idea of ​​vector control.
1.2 Hardware system solution
    This system uses the dsPICDEM1.1 motor development board of Microchip Corporation of the United States, and the main chip is dsPICD30F6010. The overall structure is shown in Figure 1. The speed sensor is used to detect the speed; the controller is used to receive the detected stator current signal and speed signal and send out a PWM signal; the drive power supply is used to detect the stator current signal and perform AC-DC-AC conversion to control the motor.

1.3 Introduction to dsPIC30F6010 chip
    dsPIC30F6010 includes 16-bit data modified Harvard structure; CPU has 24-bit width instruction; linear program storage (ROM) capacity is 4Mx24b; linear random access memory (RAM) capacity is 32Kx16b; 16×16 working register array; software stack; fast and stable interrupt response; can support 3 operands instruction A+B=C; extended addressing mode. The chip operating voltage is 5V; at -40～85℃, the maximum operation speed is 30MIPS. The related modules involved in this system are motor control PWM (MCPWM) module, analog-to-digital conversion (A/D) module, and orthogonal encoder interface (QEI) module.
1.4 Principle and selection of driving power supply
    The driving power supply design of three-phase AC asynchronous motor generally adopts AC-DC-AC mode, that is, first converting AC into DC (rectification, filtering), and then converting DC into frequency-adjustable AC (inversion).
    The driving power supply part adopts DR15A of Shanghai Jiashang Electronics. It has an integrated IPM (6 IGBTs inside), with multiple protections such as overheating, overvoltage, overcurrent, and overload. It also has functions such as two-phase stator current detection, DC bus voltage detection, and temperature detection.
1.5 Design of current sensor level conversion
    Since the stator phase current value of the AC motor changes according to the sine, it has directionality, so the value is positive and negative. The output voltage range of the current sensor in this article is -4~4 V, while the A/D conversion reference voltage range of dsPIC is 0~5 V. In order to use the controller's A/D conversion to output the correct value, the detection current signal must be level-shifted and converted.
1.6 Selection of speed sensor
    The speed sensor adopts the LF type photoelectric encoder produced by Changchun Yuheng. The main parameters are as follows:
    A, B, Z three-phase output; 5 V voltage supply; output voltage (unit: V) VH>3.5, VL<0.5; rise time <1μs; fall time <1μs; response frequency is 0-100 Hz; maximum allowable speed is 6000 r/min; starting torque is 0.05 N·m; maximum axial and radial load is 50 N; inertia moment is 1.3×10-5N-m·s2; allowable angular acceleration is 1000 rad/s2. It can meet the measurement of speed and position.
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2 System Software Design
    The software design is programmed and debugged according to the control strategy and hardware system introduced above, and mainly completes the following functions: main program of vector control, PWM time base interrupt subroutine, A/D conversion completion interrupt subroutine, fault handling interrupt subroutine, speed and current PI adjustment, etc.

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    The vector dual closed-loop control system scheme is shown in Figure 2. The closed-loop subroutine is shown in Figure 3. The specific ideas are as follows:
    (1) The stator current iA and iB output by the inverter are measured by the Hall current sensor, converted into digital quantities by the A/D converter of the dsPIC30F6010, and calculated using the formula iC=-(iA+iB). The currents iA, iB, and iC are transformed into DC components iM and iT in the rotating coordinate system through Clarke transformation and Park transformation, where iM and iT serve as the negative feedback of the current loop.
    (2) The mechanical angular displacement of the motor is measured using a 1 024-line incremental encoder with a 4-fold frequency increase, and converted into the PU value of the speed n. The speed n serves as the negative feedback of the speed loop.
    (3) As is known to all, the rotor mechanical speed of an asynchronous motor is not synchronized with the rotor flux speed, so the rotor flux position is calculated using the current-flux position conversion module. When the components iM, iT of the stator current M, T coordinate system and the motor speed n are known, the rotor flux position θ can be calculated for the calculation of Park transformation and inversion.
    (4) The deviation between the given speed nref and the speed feedback n passes through the speed PI regulator, and its output is used as the current T-axis reference component iTref for torque control. The deviation between iTref and iMref (using constant magnetism and setting its value to 0) and the current feedback iT, iM passes through the current PI regulator, and the phase voltages UMref and UTref of the M, T rotating coordinate system are output respectively. UMref and UTref are then converted into the components Uαref and Uβref of the stator phase voltage vector in the α, β rectangular coordinate system through the Park inverse transformation.
    (5) When the components Uαref and Uβref of the stator phase voltage vector and the number of sectors they are in are known, the seven-segment voltage space vector SVPWM technology is used to generate a PWM control signal to control the inverter.

3 System test
    This test uses the YS-7124 series squirrel cage three-phase AC asynchronous motor, which has a power of 370 W, a rated current of 1.94A/1.12A, a rated voltage of 220 V/380 V, a rated frequency of 50 Hz, a rated speed of 1 400 r/min, an efficiency of 69.5%, a power factor of 0.72, a stall torque/rated torque of 2.4, a stall current/rated current of 6, and a maximum torque/rated torque of 2.4.
    Open-loop SVPWM control tests, speed single closed-loop SVPWM control tests, and vector double closed-loop control tests were carried out. Taking 1000 r/min as an example, the stator current is shown in Figure 4. It can be seen that the speed fluctuation of the vector control double closed loop is smaller than the motor speed fluctuation during startup, and under the same PI adjustment parameters, the speed regulation is smoother than the single closed loop. Figure 5 is the speed waveform of the vector double closed loop control. It can be seen that the control system has a fast speed response, stable operation, and a small speed error when stable, indicating that the system operates well.

4 Conclusion
    This paper uses the dsPIC30F6010 chip to realize full software digitization. Compared with the single-chip microcomputer, it eliminates a lot of hardware while ensuring control accuracy, avoiding the instability of the hardware system that is too complicated, and is cheaper than the corresponding DSP in price. Therefore, this system simplifies the hardware circuit and saves costs. From the experimental results, it can be seen that the system has a fast speed response, stable operation, and small speed error when stable, indicating that the system operates well.