罗克韦尔自动化 Vector Control System-Based DSP & Its Embedded Internet Technology
- 关键词：vector,control,,DSP,technology,,embedded,Internet
- 作者：张新曼 韩九强 许学斌
1. Introduction
Based on DSP technology speed sensorless vector control system is accomplished and the drive is directly accessed to Internet by means of the embedded Internet technology to complete remote control. In combination with the above functions this is my paper thesis.
2. System Structure & Function
As a control mode of AC induction motor, vector control technology is the first scheme of advanced performance frequency conversion timing system. Based on mathematics model of induction motor, this technology decomposes magnetic flux current and torque current of motor winding coupling together in the selected coordinates system, and controls magnetic flux and torque separately in order to make the induction motor approach DC motor’s characteristic.
TMS320F240 which is our drive core option, is a low price and high performance 16 bit DSP in 1997 from TI corporation of USA. It is a flash EEPROM specially designed digital motor control. It not only has high performance CPU core deployed with high speed digital signal processor, but has the peripheral device function just as single chip motor control. Combined with high speed operation function of digital signal processor and powerful control capability oriented motor, it is a desired substitute of traditional multi microprocessor unit (MCU) and multi-chip design system.
Fig. 1 shows the schematic diagram of speed sensorless vector control system based DSP TMS320F240. The system makes up of main circuit, control circuit and assistant circuit. Adopting 6-cubes encapsulation power module IGBT the main circuit performs power transform. As TMS320F240 the core, the control circuit is used to complete these functions such as vector control core algorithm, PWM generator, rotor speed estimate algorithm, IP module communication program and keypad panel etc. Other available optional circuit is composed of power supply, drive circuit, IP module circuit, current and voltage detection circuit to realize these functions such as providing multi DC power supply to the system and isolation drive of IGBT etc. Key features include:
i. Current output detection
ii. Speed estimate
Fig. 1 Schematic Diagram of Vector Control System based DSP
Speed sensorless vector control system needs not any speed sensor. It uses stator voltage, stator current easy to measure and motor parameter to estimate rotor speed. Under compensating rotor’s whole magnetic chain, the speed value is estimated by adopting torque current feedback method in F240 to form closed-loop rotate speed and field-oriented vector.
iii. PWM output
PWM circuit of TMS320F240 can generate 6 routes PWM signal with programmable dead section and changeable output polar. After isolation drive unit EXB840, the signals control the main circuit’s IGBT to realize inverted output.
iv. System software design
The system software is composed of main program and PWM interrupt subprogram. The main program accomplishes system initialization, stop, run, program mode etc. The current loop’s coordinates transform, PWM signal’s generator and speed sampling program are achieved in the interrupt subprogram, see Fig. 2. So this can not only ensure speed control precision, but shorten interrupt time greatly, improving switch frequency to make system switch frequency reach 16kHz.
Along with Internet technology’s ever growing mature, TCP/IP protocol is currently available to the most popular and open grouping exchange LAN technology. Based on the existing drive appending IP module, use Ethernet as standard interface, to realize the embedded Web server technology, as network nodes the drives are connected one by one via Ethernet technology to form an organic integer. This can realize direct communication capability from locale drive to management level so as to convert a new open, shared and cooperative management mode and finally realize the whole integration solution between enterprise and management information, just as Fig. 3. The equipment engineer interviews directly the embedded Web server through HTTP protocol and can find out the run status at any moment. When any abnormality appears, network observed spot sends out alarm information for troubleshooting any where on the web to the engineer in time via ICQ or E-mail so to ensure the drive’s safety and high performance operation, thereby realize Internet network’s whole day remote control connected to the drive system in real time.
Here gives an example of IP module based IEEE 1451.2 standard, just as Fig. 4. In this standard IP module is divided into two function modules. The first is NCAP of run network protocol and application software. The second module consists of transducer and TEDS, called STIM. The key characteristic-based IEEE 1451.2 intelligent transducer interface is the digital communication protocol between transducer and network and transducer’s self-identification. 1451 standard is fused with transducer hardware in a true ‘plug and play’ fashion, so as to readily maintenance transducer and device. The following provides an overview of the various parts of the IEEE 1451.2 standard.
Fig. 4 IP Module based IEEE 1451.2
a. NCAP (Network Capable Application Processor)
The NCAP mediates between the STIM and a digital network, and may provide local intelligence. The STIM communicates with the network transparently, via the TII that links it to the NCAP.
b. STIM (Smart Transducer Interface Module)
A STIM can range in complexity from a simple single-channel sensor, or actuator, to a product supporting multiple channels of transducers. A transducer channel is denoted ‘smart’ in this context because:
-It is described by a machine-readable TEDS
-The control and data associated with the channel are digital
-Triggering, status and control are provided to support the proper functioning of the channel
c. TEDS (Transducer Electronic Data Sheet)
The TEDS is a data sheet written in electronic format that describes the STIM and the transducers associated with it. It includes data such as manufacturer’s name, type of transducer, serial number, etc. By definition, the TEDS must remain with the STIM for the duration of the STIM’s lifetime.
d. TII (Transducer Independent Interface)
The TII is a 10-wire serial I/O bus that defines:
- A triggering function that triggers reading/writing from/to a transducer
- A bit transfer methodology
- A byte-write data-transport protocol (NCAP to STIM)
- A byte-read data-transport protocol (STIM to NCAP)
- Data transport frames
e. Communication
In IP module the action order of acquisition data is that NCAP triggers; STIM reads data; After reading data, STIM acknowledges to NCAP; NCAP processes the information from STIM. The action order of performance is that NCAP writes command to STIM; NCAP triggers STIM; STIM performs command; after done with it, STIM acknowledges to NCAP.
NCAP and STIM are connected via 10 pins transducer. TII is serial communication interface based SPI (serial peripheral interface) protocol.
3. Conclusions
In conclusion, the system has the better performance & benefits as follows:
i. As the core of DSP TMS320F240, speed sensorless vector control system provides ready and accessible performance just like high work frequency, simple hardware, flexible structure, good startup performance, quick dynamic response an