TMS320F2808 realizes vector control variable frequency speed regulation system

Abstract: By using the powerful computing power and fast real-time processing capability of TI's digital signal processing chip TMS320F2808, the problem of the difficulty in implementing the complex control algorithm of vector control was solved , and the hardware and software design of the vector control variable frequency speed regulation system was completed. The experimental results show that the system has good stability, dynamic characteristics, and fast fault handling function.

Keywords: vector control; asynchronous motor; TMS320F2808

introduction

Vector control is a high-performance control technology that appeared in the 1970s, which improves the static and dynamic performance of AC speed regulation systems.

Based on the basic principles of vector control, this paper uses TI's digital processing chip TMS320F2808 with powerful computing power and fast real-time processing capabilities as the control chip, designs a fully digital vector control hardware system, and gives the protection circuit, current detection circuit, speed detection circuit, and part of the program flow.

1 Basic principles of vector control

The basic theory of vector control is to simulate the law of DC motor torque control on a three-phase AC motor, apply the coordinate transformation Clarke transformation to convert the three-phase AC system into a two-phase AC system, and then convert the two-phase AC system into a rotating DC system through Park transformation. In the rotor magnetic field orientation coordinates, the stator current vector is decomposed into the excitation component that generates the magnetic flux and the torque component that generates the electromagnetic torque, and the two components are made perpendicular to each other, realizing the decoupling of the stator current excitation component and the torque component, achieving the purpose of controlling the magnetic flux and torque of the asynchronous motor separately, thereby obtaining the same excellent static and dynamic speed regulation performance as the DC motor speed regulation system. Its basic principle is shown in Figure 1.

2 System Hardware Circuit Design

2.1 Main circuit

This system adopts a voltage-type "AC-DC-AC" frequency conversion structure in the main circuit, which is mainly composed of a rectifier circuit, a filter circuit and an inverter circuit. In order to make the main circuit structure simple and easy to replace and repair the components, this design adopts a modular structural design scheme. Figure 2 is a block diagram of the asynchronous motor vector control system based on TMS320F2808.

This design uses Mitsubishi's rectifier inverter brake module CP10TD1-24A. Its features are: using LPT-CSTBTTM silicon chip technology and integrated injection molded small package for rectification, inverter, brake, and NTC temperature detection, low saturation voltage drop, low module thermal resistance, and built-in NTC temperature sensor.

2.2 Control loop

Since the vector control system requires a large amount of calculation, the control loop uses TI's DSP chip TMS320F2808 and its peripheral circuits to implement the vector control core algorithm and related voltage and current detection and processing functions.

2.2.1 Power supply circuit

Figure 3 shows the power supply circuit. In order to improve the stability of the control system and extend the service life of the device, this design uses a high-performance voltage regulator chip and a low-dropout voltage regulator LM1117 to provide a reliable power supply for the TMS 320F2808. 3.3 V and 1.8 V fixed voltage output chips are used to power the DSP, respectively. The output current can reach 800 mA, the output voltage accuracy is within ±1%, and it has current limiting and thermal protection functions.

2.2.2 JTAG simulation debugging interface circuit

In order to facilitate the connection between the speed control system and the host computer, realize the access of the simulator to the DSP and simulate and debug the vector control speed control program, the JTAG simulation and debugging interface circuit is indispensable in the variable frequency speed control design. The specific circuit diagram is shown in Figure 4.

2.2.3 Overvoltage and undervoltage protection circuit

In order to improve the reliability of the system and better protect the inverter components and asynchronous motors, the speed control system should be equipped with a set of accurate protection measures to prevent various faults. This paper adopts the over- and under-voltage protection circuit of the DC bus voltage, as shown in Figure 5. When the detected DC bus voltage exceeds or is lower than the predetermined voltage, all control signals will be turned off, thereby playing a protective role. Among them, LM393 is a dual voltage comparator.

2.3 System detection circuit

The detection circuit is an important part of the speed control system. Its function is to convert the detected signal into a DSP recognizable signal after analog/digital conversion, and then output the required signals of each part of the circuit through a certain algorithm, so as to realize the predetermined function and provide necessary protection for the system and the motor. Therefore, whether the detected signal is reasonable and accurate is directly related to the reliability and control accuracy of the entire system. According to the needs of the vector control system, this paper carries out stator current detection and motor speed detection.

2.3.1 Stator current detection circuit

In the vector control system, the accuracy and real-time performance of the stator current are important factors affecting the control accuracy of the speed control system. This paper uses the Hall current sensor TBC-05SY with high accuracy, good linearity, wide bandwidth, fast response, strong overload capacity and loss-free measurement circuit to detect the stator current. Figure 6 shows the stator current detection circuit. Among them, LMC6464 is a low-power, rail-to-rail input and output CMOS operational amplifier.

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