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(a) Three-phase stationary coordinate system 
(b) Two-phase stationary coordinate system 
(c) Two-phase rotating coordinate system Fig. 1 The principle of the magnetic field orientation control Since the physical quantities on the stator side of the AC motor are all AC quantities, the space vector rotates at a synchronous angular frequency of 1, making control and calculation difficult. Therefore, it is necessary to transform the coordinate system from a stationary coordinate system to a synchronous rotating coordinate system by means of coordinate transformation, and the space vector is converted into a direct current amount and controlled. To illustrate the principle of transformation, three-phase stationary coordinate systems, two-phase stationary coordinate systems, and two-phase rotating coordinate systems are defined as shown in Figs. 1a, b, and c. In FIG. 1a, it is assumed that a three-phase alternating current motor is energized with three-phase balanced sinusoidal currents iA, iB and iC to generate a three-phase stator synthetic magnetomotive-space vector Fj rotating at a synchronous angular frequency w. In Fig. 1b, the same Fj can be produced when the two phase fixed windings a, b (spatial positions are 90° out of electrical) pass through the two-phase balance currents ia, ib (90° electrical angle in time). The aforementioned coordinate system is stationary. In Fig. 1c, if two direct currents id, 1q are passed through two mutually perpendicular windings d, q, two fixed magnetomotive forces Fd and Fq will be generated respectively, and d, q will be generated. The coordinate system rotates at the synchronous angular frequency w at the same time, and Fd and Fq also rotate with it, generating Fj equivalent to the foregoing. Therefore, the three-phase winding of the motor can be equivalent to two sets of windings in the d and q coordinates. In the rotating coordinate system, each vector of the motor becomes a stationary vector, and each component thereof is a direct current. Therefore, it is easy to determine the relationship between the components of the torque and the controlled vector, and the components of the controlled vector are calculated in real time. Value (DC component). Since the DC components of these controlled vectors do not physically exist, the coordinate transformation is also required. From the rotating coordinate system back to the stationary coordinate system, the above-mentioned DC-quantity is converted into a physically existing AC-amount, in the stationary coordinates. The system controls the amount of communication. 
Figure 2 The principle of magnetic field orientation control The magnetic field oriented control principle is shown in Figure 2. The speed difference is output by the amplitude of the stator current vector after adjustment by the speed regulator: the phase of the stator current vector is obtained after being detected and calculated by the rotor position detection circuit, and the amplitude of the stator current vector is given in the current given step. Summarize and convert to generate the instantaneous three-phase current reference signal: the current reference signal is compared with the converted actual current signal, and then adjusted by a current regulator and output a Pulse Width Modulation-PWM signal to control AC servo motor. The key is to control the amplitude and spatial position of the stator current vector by decoupling. Direct torque control theory The principle of direct torque control is shown in Figure 3. The theory abandons the decoupling control in the field-oriented control theory and is oriented by the stator magnetic field. The space vector analysis method is used to calculate the actual values ​​of magnetic flux and torque in the stator coordinates using the measured values ​​of the three-phase stator currents and voltages, and compare them with the given values ​​of the magnetic flux and torque, respectively. After adjusting with the flux regulator, the six switch states of the inverter are used to directly control the switching state of the inverter directly. That is, the voltage space vector is used to control the rotation speed and direction of the stator flux linkage to change the size of the magnetic flux angle, and the purpose of controlling the torque is achieved by utilizing the proportional relationship between the torque and the magnetic flux angle. It eliminates the tedious vector transformation between the stationary and rotating coordinates and a large number of coordinate transformation calculations, eliminating the need for a simplified motor math model, and without the usual PWM signal generator. It has the characteristics of simple control system structure, direct control means, and clear physical concept of signal processing. The torque response of the control system is rapid, without overshoot, which is an AC speed regulation method with high dynamic and static performance. 
Fig. 3 Principle of direct torque control Fig. 2 Digital AC servo control module DSP digital AC servo control module and its structure We adopt the digital AC servo control module based on DSP, and design two parallel control templates. The template integrates a DSP minimum system, an In-System Programming-ISP device, an A/D conversion device, and the like. With this template, only the hardware control module required by the software can be configured according to the control object. In order to reduce the complexity of the template structure and improve versatility and reliability, ISP devices form a single-chip digital input/output (I/O) hardware circuit. In actual application, only by calling the I/O software and control software, it is possible to form an all-digital magnetic field orientation control module and an all-digital direct torque control module. The former is applied to the control of a synchronous motor, and the latter is applied to the control of an asynchronous motor. In the experiment, the motor we used was an AC permanent magnet synchronous servo motor, so the field oriented control module was used. Its structure is shown in Figure 4. 
Figure 4 The structure of the magnetic field orientation control module The working principle is: The hardware (A/D, ISP) converts the feedback signal into a digital signal. The DSP samples and calculates the digital signal, according to the speed given signal, according to the determined magnetic field. The directional control law controls the controlled object, and its control signal is output to the PWM signal generation circuit in the ISP device to generate the required PWM signal, and the motor is controlled by the intelligent power device. The digital I/O circuit uses the ISP device ispLSI1032-80 to design the digital I/O circuit. Its integrated scale is a 6000PLD equivalent gate. One ISP device can completely accommodate the entire digital I/O circuit, and the parameters of the gate and flip-flop in the same chip are consistent. In addition, the anti-interference performance is greatly improved compared to the circuit composed of separate devices. The digital I/O circuit is shown in Figure 5. 
Figure 5 Digital I / O circuit using the ISP device's output tri-state buffer characteristics, constitute the output tri-state gate, connected to the DSP data bus, gate control signal from the DSP's read / write signal, chip select signal in the gate signal generation The circuit is combined and connected to the enable terminal of the tri-state gate. The digital quadrupling circuit subdivides the quadrature coded pulses (A-phase, B-phase) generated by the photoelectric encoder to generate a quadrupled pulse and a motor steering signal for counting and sampling. The sampling signal constitutes a circuit to synthesize a sampling pulse and a quadruple frequency pulse sent from the DSP, and sends a pulse signal in the order of data latching, interrupt application, and counter clearing to control the sequence of the sampling logic. In the application, according to the I/O requirements of different control objects, the related I/O software is called and downloaded into the ISP device, and the required digital I/O circuit can be formed. 3 Experimental results We conducted experiment on DSP AC AC servo control module in AC permanent magnet synchronous motor. The motor used is MFA150MB5. Rated output power 1.5kW, rated current 7.5A, rated speed 2000r/min, encoder output pulse 2500 pulse / r. The experimental results are shown in Figures 6 and 7. 
Figure 6 motor phase current waveform 
Figure 7 motor speed step response characteristic curve Figure 6 is the phase current waveform of the motor: Figure 7 is the speed step response characteristic curve from standstill to 500r/min when the motor is unloaded. The experimental results show that the designed DSP digital AC servo control module has higher control accuracy and faster response speed. The module was tested in a multi-coordinated linkage numerical control system. The result of the operation shows that, as one of the coordinates of the closed-loop speed control inner loop, it can ensure the position servo control precision meets the design requirements. 4 Conclusion The DSP digital AC servo control module designed has the characteristics of high integration, compact structure, easy maintenance and debugging, and adaptability to various control objects. The module has a wide range of applications. In addition, for DC motor servo control, stepping motor control and AC linear motor control, control software can also be designed as needed to form the required control module.
Digital AC Servo Control Strategy and Design
Modern AC servo system requirements for control are: fast response, high precision, and low torque ripple. The realization of high-performance control of AC motor instantaneous torque is a key factor to meet these requirements. Therefore, the control strategies of modern high-precision AC servo systems mostly adopt the field-oriented control theory and direct torque control theory. In addition, with the development of microelectronics technology, digitization has become an important development direction of AC servo systems. The digital control system composed of digital signal processing (DSP) devices not only has high accuracy and high reliability, but also simplifies the system structure and increases system functions and flexibility. 1 Digital AC servo control From the current development status of AC servo control system, the field-oriented control theory and direct torque control theory have their own advantages and applications are not the same. The control of synchronous motors generally uses field-oriented control, especially for the control of AC permanent magnet synchronous motors. It has the characteristics of simple control structure and easy realization of control software. It can be used for the control of asynchronous motors, but recent studies In direct torque control, this is mainly because the field-oriented control of asynchronous motors is extremely complicated, and the control effect is far inferior to synchronous motors.