Introduction to FPGA
Field Programmable Gate Array FPGA (FieldProgrammable Gate Array) is a universal user programmable device first developed by Xilinx in 1984. FPGA not only has the high integration and versatility of gate array devices, but also has the flexibility of user-programmability of programmable logic devices.
FPGA consists of programmable logic cell array, wiring resources and programmable I / O cell array. An FPGA contains rich logic gates, registers and I / O resources. One FPGA chip can realize the system realized by hundreds or even more standard digital integrated circuits.
The structure of FPGA is flexible, and its logic unit, programmable internal wiring and I / O unit can be programmed by the user, and can realize any logic function to meet various design requirements. Its fast speed, low power consumption, strong versatility, especially suitable for the design of complex systems. Using FPGA can also achieve dynamic configuration, online system reconstruction (you can change the function of the circuit as needed at different times of the system operation, so that the system has a variety of space-related or time-related tasks), and hardware softening, software hardening and other functions.
In view of the relatively large scale and complex functions of the controller of the high-frequency fatigue testing machine, in the development process, on the basis of the traditional testing machine controller, through the combination of FPGA technology and microcomputer technology, to comprehensively improve the controller system The performance of the machine has improved the working efficiency, control accuracy and reliability of the electrical system of the whole machine, and it is easy to operate without lack of advanced technology.
2 Controller structure and content
The overall structure of this control system, the lower computer is the core of the entire high-frequency fatigue testing machine controller. It is used to generate control signals and data to control the testing machine, process feedback signals, and perform data communication with the host computer. The strength of its control function also directly affects the performance of the entire controller. The waveform generator in the picture is used to excite and maintain the vibration of the electromagnetic vibrator. Here, the waveform generator should output a sine wave.
3 The technical route adopted by the system
Based on the realization of technical parameters and functional requirements, the system has adopted the following main technical routes in combination with the current microcomputer technologies such as microcomputers and FPGAs:
(1) The lower computer is the core of system control. Because the control scale of this system is relatively complex, the control object has certain specialities (such as high frequency, high load, etc.), and involves the control of the motor, so instead of using the traditional 8-bit machine, consider the use of relatively more powerful and speed Faster 16-bit machine-87C196 series.
(2) The exciter requires the input waveform to be a sine wave, and the test frequency range is 80 to 250 Hz. In addition, the system should also be able to perform a frequency sweep test. In the frequency sweep test, the system sweeps the frequency in steps of 1 Hz (coarse adjustment), and then fine-tunes on the basis of the coarse adjustment (in steps of 0.1 Hz) to determine the resonance point of the system. It can be seen that the circuit module that can generate a waveform with an accuracy of 0.1 Hz is a critical part of the overall system design and one of the design difficulties. This part cannot be achieved or is difficult to achieve if it is through a microcontroller or other special chips. The system uses FPGA as the waveform generator, as shown in the dotted frame in Figure 1. The advantages of this are: high speed (generally the chip frequency is at least a few tens of megabytes, even hundreds of megabytes) and can meet the above precision requirements; it is realized by digital circuits and has good anti-interference; it can also integrate other logic circuits into the chip, Many discrete components are eliminated, and the volume is also reduced; the waveform can be changed as needed.
(3) The DC speed regulation is realized by voltage transformation, and the voltage transformation is completed by the controllable rectifier using thyristors. The variable voltage is output to the phase-shifting trigger through the single-chip microcomputer, and the trigger outputs the controllable conduction angle to the controllable rectifier to realize the adjustment of the motor speed. Helps to improve the reliability of the system.
(4) Some important signals of the system are filtered by a digital filter, and the digital filter is implemented by an FPGA. Compared with software filtering, this method is beneficial to improve the filtering effect of the signal, and the filtering speed is greatly improved.
4 Part of the module design
The FPGA part can be divided into two modules, of which the sine wave generator module can be subdivided into several small modules, as shown in Figure 2.
4.1 Latch design
The latch is used to latch and stabilize the frequency data sent by the single-chip microcomputer in the FPGA, and can be formed by using the on-chip latch resources (or using triggers).
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