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System hardware architecture

As digital printed circuit board and semiconductor technology is increasingly mature, the digital signal, the digital circuit in the application is more and more big, the proportion of showing at the same time, more and more advantages: convenient for computer processing control, reduce the signal interference, improve the anti-interference ability, easy to debug, also facilitate the diagnosis, fault-tolerant technology such as insertion. With the enhancement of the main frequency of the embedded processor, the enhancement of the in-chip control function and the further improvement of the frequency and PWM waveform, the integration of the power supply control system can be improved.

The power supply to the output voltage and current signal sampling, PID control, after the output PWM waveform to adjust the output voltage. Output voltage Provides stable output of high voltage and high current for electroplating by charging and discharging large capacity tantalum capacitors.

The system includes PID controller,PWM output,AD sampling, constitute a single closed loop system. The front-end three-phase AC power supply is input to the switching power supply rectifier module, which outputs a steady DC voltage after rectification and filtering. The DC voltage is directly output to IGBT module. The high AD converter changes the output voltage and current signal from analog signal to digital signal to supply S3C44BO for digital PlD operation. After PID control operation, S3C4480 outputs PWM to IGBT to form a closed-loop system to control the stable output of voltage and current, so as to realize the control system of switching power supply.

For PID operation and PWM wave output module, higher requirements. Through calculation and examination, we select S3C4480 from SAMSUNC, which is a 32-bit CPU based on ARM7TDtMI architecture and has up to 59MIPS computing speed. Its specific functions and features are as follows:

The calculation speed is up to 59 MIPS, which fully meets the real-time requirements of complex PID controller.

16 bit timer, up to 0.03 μs PWM pulse wave, and DEADZONE function;

As many as 8 external interrupt sources can respond to the system external fault information in real time.

Internal embedded LCD) controller, and has DMA channel, so that the voltage and current value can be displayed in real time on the LCD;

Up to 71 universal 10-port lines for easy expansion of external interfaces;

The embedded lIC interface controller can save system information in EEPROM for the reference of system operators.

Internal watchdog function can make the system automatically reset in the case of software or hardware error, to ensure the safe and normal operation of the system;

Two asynchronous serial interfaces (UART) can easily realize the communication with the host computer;

Expandable mass storage provides sufficient space for software.

First, the system uses touch screen and LCD as man-machine interface. S3C44BO internal integrated LCD controller, can support up to 320*240 resolution,256 color sTN - LCD), and through THE DMA channel connected with the CPU, can quickly and dynamically display color graphics, replacing the manufacturer's traditional 5L series of single-chip microcomputer and LED digital tube of the man-machine interface, so that workers operate more convenient. S3C44BO external GPIO interface to provide a variety of external signals as listed in Table 1.

8 external interrupts, to meet the immediate shutdown response to overcurrent, overvoltage, phase loss, overtemperature and other special circumstances. S3C44BO with external memory interface, through the expansion of FLAsH SST39VF160 and SDRAM HY641620 to ensure that the digital control system has enough space to save and run programs. Due to the design requirement of 1/1000, we did not choose S3C4480 IOBIT - ADC, but chose AD7705, a dual-channel, 168IT△ 1 ∑ ADC, and connected with THE CPU through the SIO synchronous port.

2 PWM control principle

There is an important conclusion in sampling control theory: when the narrow pulse with equal impulse and different shape is applied to the inertia link, the effect is almost the same. PWM control technology is based on the theory of the conclusion, the conduction of semiconductor switching devices and turn off control, make the output end to get a series of equal amplitude and pulse width are not equal, using these pulsed column instead of a sine wave or other needed waveform, and according to certain rules for each pulse width modulation.

In this system, THE PWM waveform is output by THE CLOCK TIMER0 output port T0UTO of THE CPU S3C4480. Because the required output frequency of 30 kHz PWM wave, and Therefore, by setting the registers of TCFGO and TCFGl, the 4BIT divider is set to O. 5, the preset register is set to L, and the count comparison register TCNTB0 is set to 1000. In this way, when the main frequency of S3C4480 is 66MHz, the PWM wave frequency of TOUT0 output is 30 KHz. When TIMER0 starts, the timer controls the PWM wave level to change every time the value of TCNTB0 is the same as the down-counter value of the timer. So that the value of TC-NTB0 can control the duty cycle of the PWM wave, increase or decrease by 1, then the duty cycle of the PWM output increases or decreases by one thousandth, thus reaching one thousandth. Figure 2 is the output PWM waveform diagram. We can see that the PWM waveform output by TOUTO through the dedicated timer output is very good. After testing, both rising edge and falling edge are at NS level.