Abstract: Vector control is a high-performance AC motor control method, which has the advantages of small control torque and less harmonic components. This paper introduces a kind of vector control variable frequency speed control system design based on TI's TMS320F2812, describes the structure and design features of each hardware functional unit, and presents the design scheme and the design method of hardware and software.
Keywords: asynchronous motor; vector control; current regulation
DSP-based vector control of asynchronous electromotor
Ma Zhaoxun Yang Guowei
(Harbin Jiuzhou Electric Co., LTD. Haerbin 150081 Heilongjiang)
This paper introduces a system design that based on vector control VVVF to TI's TMS320F2812 as the core, description of the Hardware functional unit of the structure and design features, and gives the design proposal and design methods of hardware and software.
Key words:asynchronous electromotor;vector control;current Regulator
1 Introduction
In recent years, with the rapid development of power electronics, the appearance of various new types of high-power semiconductor devices, such as IGBTs, has made power electronic devices move toward large-capacity, high-frequency, easy-to-drive, low-loss, and intelligent modularization. To promote the rapid development of AC drive. It has entered the phase of competition with DC drives and has a tendency to replace them. Compared with DC motors, AC motors are simple in structure, low in price, and reliable in operation. The rapid development of AC motor control theory, microcomputer technology, and especially power electronics technology has led to great development in high-performance AC variable frequency speed control technology. Widely used in various fields of production and life. Digital signal processor (referred to as DSP) is a microprocessor with special structure which is rapidly developing at present. It integrates three disciplines of microelectronics, digital signal processing and computer technology. The internal structure of DSP adopts the Harvard architecture separated from the program bus and the data bus. It has dedicated hardware multipliers and adopts pipeline operations, so it can quickly implement various digital signal processing algorithms and is suitable for real-time control.
2. Vector control principle of asynchronous motor
Vector control realizes the decoupling control of the motor torque and flux by transforming the current, voltage and flux linkage of the motor into the synchronous coordinate system, so as to achieve fast torque response and higher efficiency operation. This method controls the amplitude and phase of the AC at the same time and is therefore called vector control. The vector control simulates the mechanism by which the commutator of the DC motor maintains perpendicular magnetic flux and the armature magnetomotive force, so that the control performance of the AC motor reaches the level of the DC motor.
Induction motor vector control can be divided into rotor field orientation, stator field orientation and air gap field orientation vector control according to the different orientation directions of the adopted coordinate system. Stator field-oriented vector control Although the decoupling of magnetic flux and torque is incomplete, decoupling control can be achieved by feed-forward compensation. Because stator magnetic field orientation control directly controls the stator flux, this makes it possible to make maximum use of the bus voltage and the current output capability of the inverter, and is more suitable for the control under the weak magnetic field. Air gap field oriented vector control employs an airgap flux linkage that can be directly measured by a sensor. The saturation of the motor flux is consistent with the air gap flux and is more suitable for dealing with saturation effects, but its flux and torque are decoupled. Not completely, the control is a bit complicated. The rotor field-oriented vector control, excitation current and torque current decoupling the most complete, and thus in the asynchronous motor vector control has been widely used.
Voltage equation: ![]()
For asynchronous motors, ![]()
Flux equation: ![]()
Matrix expression: ![]()
Mechanical equations of motion: ![]()
In the study of asynchronous motor vector control strategy, two coordinate systems are mainly used: ab coordinate system and dq coordinate system.
3. Hardware control circuit section
The control chip of this system adopts the latest digital signal processor TMS320F2812 of TI Company, a special-purpose DSP chip that is specially applied in the field of motor and other motion control. The entire system uses AC-DC-AC variable-voltage inverter circuit. The main circuit consists of an inverter circuit composed of a rectifier bridge, a filter circuit, and an intelligent module. The control circuit takes the DSP chip TMS320C2812 as the core to form a fully functional control circuit. The current detection circuit consists of a Hall sensor circuit connected to the output of the inverter bridge. The phase voltage detection circuit is a Hall sensor circuit. The interface circuit mainly refers to the keyboard and display circuit and the memory expansion circuit. When designing the hardware circuit of this system, modular chips are used to reduce the complexity of peripheral circuits. The motor model can be derived and compensated by the feed forward method. The disturbance of the speed controller needs the observation of the load torque to compensate; the performance indicator of the current regulator can be determined after the switching frequency and the motor parameters are determined, and the speed is adjusted. The device may want different indicators for different applications. Therefore, the current regulator design of the general product is built-in, only the speed regulator allows users to manually adjust according to different application requirements.
4. Current regulation in vector control
In an asynchronous motor, whether the electromagnetic torque or the magnetic field is controlled by the stator current of the motor, it can be considered that the control effect of the stator current directly affects the performance of the speed control system. Since the current regulation is essentially the same as the flux and torque regulation, in many cases these two regulation steps are often combined and are not strictly differentiated. The actual control system often needs to be simplified or combined according to different requirements, and the task of the current regulator is to select the correct voltage vector.
The basic reason for choosing the stator current as a control variable is that when the magnetic field is oriented, the electromagnetic torque and flux are directly controlled by the torque component and magnetic flux component of the stator current after decoupling, and the stator current can be effectively controlled by controlling the stator current. Torque and flux. In addition, the current regulator can be regarded as a characteristic of an ideal current source in a certain sense, and the degree of control system can be reduced and the level of the control system can be reduced irrespective of the dynamic behavior of the stator side of the motor due to resistance, inductance, or back electromotive force. The complexity of the control link. 5. Control System Software Design
All the control of the induction motor in this system is realized by the software of the DSP chip TMS320C2812. The software program consists of a main program and a timer underflow interrupt subroutine. The main program's job is to initialize, convert the frequency adjustment ratio of the external input to the corner frequency, and determine the amplitude of the reference voltage according to the U/f curve. The interrupt subroutine's job is to calculate the compare value of the three compare registers of the next PWM cycle in each PWM cycle and send them to the compare register.
6 Conclusion
This paper takes the asynchronous motor as the control object and applies the vector control technology in the speed control system of the asynchronous motor. The vector control is much more advanced than the previous V/F control. In particular, the encoder performs speed feedback. It can complete the torque control, and the low-speed performance is greatly improved. General-purpose frequency converter usually adopts SPWM control mode, and generates SPWM wave through real-time calculation. The real-time calculation requires very high operation speed of the controller, and DSP is the most ideal controller that meets this requirement and is the most cost-effective controller. The speed of the motor has a relatively fast speed and strong anti-disturbance capability, achieving satisfactory control results.
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