As a method of AC asynchronous motor control, vector control technology has become the preferred solution for high-performance variable frequency speed regulation systems. In vector control systems, the observation accuracy of flux linkage directly affects the control performance of the system. In a rotor flux linkage oriented vector control system, torque current and excitation current can be completely decoupled [1]. Generally speaking, there are two methods for rotor flux linkage observation: current model method and voltage model method. The current model observation method of flux linkage requires the rotor time constant of the motor, which is easily affected by temperature and magnetic saturation. To overcome these shortcomings, it is necessary to observe the rotor parameters of the motor in real time, but this will make the system more complex. The voltage model observation method of flux linkage does not contain rotor parameters and is less affected by changes in motor parameters. Vector control has a large computational load and requires a certain real-time performance, which puts forward higher requirements for the operation speed of the control chip. This paper introduces a design method for an asynchronous motor vector control system, which uses a voltage model observer [2] to estimate the rotor flux linkage. In view of the error accumulation and DC drift problem of the integral link, an integrator with saturation feedback [3] is used to replace the pure integral link in the voltage model observer. The entire algorithm is implemented on the TMS320F2812 DSP chip, which boasts fast processing speed and ensures excellent real-time performance of the system. Asynchronous Motor Vector Control Strategy The basic principle of vector control is: based on the principle of magnetic flux equivalence, the three-phase system is equivalent to a two-phase system using coordinate transformation. Then, through synchronous rotation transformation oriented by the rotor magnetic field, the stator current is decomposed into two mutually orthogonal components: the excitation current component isd and the torque current component isq. That is, the armature reaction magnetic field generated by these two current components is used to equivalently represent the armature reaction magnetic field generated by the original three-phase stator winding current. Then, isd and isq are controlled independently, thus allowing a three-phase asynchronous motor to be controlled as an equivalent DC motor, achieving the same good static and dynamic performance as a DC speed control system. The principle block diagram of the asynchronous motor vector control system introduced in this paper is shown in Figure 1. [align=center] Figure 1 Induction Motor Vector Control System[/align] The system adopts a double closed-loop structure with speed outer loop control and current inner loop control. When the system's operating synchronous frequency is below the motor's rated frequency, the excitation current ISD is the motor's rated excitation current; above the rated frequency, field weakening control is employed. The system shown in Figure 1 uses three PI regulators. The speed regulator outputs the setpoint value of the torque current based on the speed difference, while the torque current regulator and excitation current regulator adjust the torque current and excitation current components, respectively. The rotor flux linkage observer observes the magnitude and angle of the rotor flux linkage based on the actual motor input current and voltage. From a control theory perspective, the accuracy of a control system primarily depends on the accuracy of the feedback signal. Therefore, the accuracy of rotor flux linkage-oriented vector control mainly depends on the accuracy of flux linkage estimation. As can be seen from the observation equation of the flux linkage voltage of the asynchronous motor [img=165,37]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf22.jpg[/img] (1), the flux linkage is obtained by integrating the back electromotive force. In order to solve the problems of integrator saturation initial value caused by pure integration, this system adopts an integrator with saturation feedback [3] to replace the pure integration link. Its principle block diagram is shown in Figure 2. The output of the flux linkage observer is: [img=141,39]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf23.jpg[/img]（2） Where, [img=131,33]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf24.jpg[/img], [img=14,18]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf25.jpg[/img] is the back electromotive force of the motor; and is the output of the saturation circuit. When the observed rotor flux linkage is less than or equal to the given value of the rotor flux linkage, i.e., [img=57,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf26.jpg[/img], [img=43,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf27.jpg[/img]; when the observed rotor flux linkage is greater than the given value of the rotor flux linkage, i.e., [img=57,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf28.jpg[/img], [img=38,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf29.jpg[/img]. Therefore, when [img=57,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf30.jpg[/img], the flux linkage observation model is: [img=47,33]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf31.jpg[/img] (3) The above observation model becomes a pure integral element, that is, the ordinary voltage observation model. When [img=56,20]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf32.jpg[/img], the flux linkage observation model is: [img=128,36]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf33.jpg[/img] (4) As can be seen from the above formula, when the size of [img=12,16]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf34.jpg[/img] is reasonably selected, even if there is a DC bias signal in the input, the rotor flux linkage observation model output will not show integral saturation, which can effectively suppress DC offset. The selection of [img=12,16]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf34.jpg[/img] in the model is crucial. Selecting it too high will result in a large DC component in the output, while selecting it too low will cause significant output distortion. In this system, [img=53,21]http://www.ca800.com/uploadfile/maga/servo2007-2/___wmf34.jpg[/img] (rotor flux linkage given) is used. [font=黑体] [color=black] Hardware Implementation of the Vector Control System [/color][/font] The structural block diagram of the AC variable frequency speed regulation system based on the TMS320F2812 vector control scheme is shown in Figure 3. Figure 2 Rotor flux linkage voltage observation model with saturation feedback Figure 3 Circuit structure diagram of the vector control system [align=left] The entire system is an AC-DC-AC transformer-frequency converter circuit, consisting of three main parts: the main circuit, the control circuit, and the auxiliary circuit. The frequency converter used in the main circuit is an AC-DC-AC voltage source transformer-frequency converter, which consists of a diode rectifier and a six-tube packaged IGBT power module to form the inverter. The control circuit adopts a digital design, with a DSP digital processor as the core, to complete the vector control core algorithm, SVPWM pulse generation, related current detection and processing, and communication with the host computer. The auxiliary circuit is the switching power supply section, which provides the required voltage to each chip in the system. The entire system control strategy is implemented using a DSP (TMS320F1812). This is a fixed-point chip designed by TI specifically for motor control, with a main frequency of up to 150MHz. It has two on-chip event managers (EVA and EVB), each with two general-purpose timers, six PWM output channels with programmable dead-time functionality, two external hardware interrupt pins, six capture units, and two quadrature encoding units. These functional modules greatly facilitate algorithm calculations and data output during motor control. Power Drive Section The asynchronous motor's power drive uses an AC-DC-AC PWM method, employing a PIM (Power Integrated Module) FP75R12KE3, which includes a three-phase uncontrolled rectifier circuit, an inverter circuit composed of six IGBTs, and an IGBT for energy-saving braking. The PWM1-6 pins of the DSP provide PWM trigger signals, which are used to control the on/off state of the IGBT in the power module through the isolation drive circuit to achieve SVPWM inverter output. The two PWM trigger signals of the same bridge arm are interlocked to effectively prevent the shoot-through phenomenon of the bridge arm in hardware. At the same time, the fault signal is output to the PDPINTA pin of the DSP at the corresponding fault pin, and the PWM pulse output is blocked through hardware interrupt. [font=黑体]Switching power supply section[/font] The switching power supply adopts a single-ended flyback topology design[4], and the control chip adopts the current-type PWM generator chip UC3844. The resonant resistor and resonant capacitor are adjusted to make it work at 80kHz. The control mode adopts voltage outer loop control and peak current inner loop control mode. TL431 and optocoupler NEC2501 form an output voltage sampling circuit to feed back the output voltage of the secondary side of the transformer to UC3844. The UC3844 compares the actual feedback voltage with its own generated 2.5V reference voltage to generate an output voltage error, which is then amplified by an error amplifier and used as a threshold voltage, forming the outer voltage loop. Simultaneously, it samples the primary current of the switching transformer and sends the threshold voltage and the sampled current voltage together to a current comparator, forming the inner current loop. When the sampled current voltage exceeds the threshold voltage, the comparator output turns off the power transistor and maintains this state until the next cycle. Therefore, based on the change in output voltage, the pulse width modulator output pulse width is adjusted accordingly to achieve a stable output voltage. [Simulation and Experimental Results ] This paper uses MATLAB to simulate the rotor flux linkage observation model shown in Figure 2. The simulation waveforms are shown in Figures 4 and 5. Figure 4 Comparison of a pure integrator and an integrator with saturation feedback. In Figure 4, curve 1 is the input signal with DC offset, curve 2 is the output signal of the ordinary voltage observation model, and curve 3 is the output signal of the voltage observation model with saturation feedback. It can be seen that due to the addition of positive DC offset, curve 2 shows a significant deviation as the error accumulates. Curve 3, after feedback from the saturation characteristic circuit, only exhibits some distortion in its upper part. Figure 5 shows the observed waveform of the rotor flux linkage obtained using the flux linkage observation model shown in Figure 2, demonstrating the good sinusoidal nature of the flux linkage signal. Figure 5: Lissajous waveform of the rotor flux linkage signal. The experiment of this system was conducted on an 11kW Y-connected three-phase asynchronous motor. The clock frequency of the DSP TMS320F2812 was set to 150MHz, the switching frequency of the SVPWM was 5kHz, and the dead time was 3.2μs. The voltage and current waveforms at a frequency of 20Hz are shown in Figure 6, and the current and voltage waveforms at a frequency of 40Hz are shown in Figure 7. Figure 6 shows the output voltage and current waveforms at 20Hz. Figure 7 shows the output voltage and current waveforms at 40Hz. [Conclusion] This paper details the design method of each part of an asynchronous motor vector control system based on DSP. This system features simple hardware circuitry and flexible structure. The voltage observation model with saturation feedback loop used provides high accuracy in observing rotor flux linkage and effectively suppresses errors caused by DC drift and initial value uncertainty. Simulation and experiments demonstrate that the asynchronous motor vector control system designed using this method has excellent control performance.