14KV—5KW high voltage capacitor charging power supply-EEWORLD

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1 Introduction

This charging power supply is for a scientific research project, which requires a charging capacitor of 3000uF, a voltage range of 4000V--14000V, a charging accuracy of AU=|30V+U* 2000ppm|, a power supply voltage of 380V/50Hz, an operating frequency f of the energy converter greater than or equal to 15KHz, a maximum output power of the energy converter greater than or equal to 5KVA, and each charging process is completed within 1 minute.

2 Overall power supply scheme

Since the switching frequency of the high-frequency high-power converter is greater than 15KHz, this scheme adopts a hard switching method with a switching frequency of 18KHz. The power device is composed of intelligent IPM modules. In order to reduce the leakage current of the transformer caused by the distributed parameters, the transformer is divided into 3 transformers in series, so that the output voltage drop of each transformer is less than 5KV, which is also conducive to the realization of the rectifier output at the back end. The controller uses a 320F240 power conversion and motor control dedicated processor. The power supply principle block diagram is shown in Figure 1:

3 Detection of output voltage and current

The output current is detected by Hall element. The actual charging current output by the power supply fluctuates, and the average value of multiple points should be taken. The output is a DC high voltage. A large resistor can be connected in parallel to convert the voltage into current and measure it with a Hall element. It should be noted that the high-voltage isolation of the detection circuit is required. In this power supply, an insulating ceramic tube is added to the magnetic ring of the Hall element.

[page]4 Control strategy

Because the load is a large capacitor, the voltage change across the capacitor is relatively stable (the charging current is stable); so it is only necessary to ensure that the charging current is stable. By adjusting the trigger pulse width of the power device of the inverter part of the power supply, the output filter inductance and capacitor values can be reasonably selected to make the charging current stable. Therefore, the control strategy is that the trigger pulse width of the power device of the inverter part of the power supply increases according to time, and the sampling values of the output current and voltage are mainly used for protection and determination of the trigger pulse width.

Since the load of this power supply is a fixed large capacitor, it is a fixed load power supply; simulation is first performed and then multiple experiments can be performed to determine the optimal values of the output filter inductance and capacitance, the initial width of the trigger pulse, and the incremental step of the trigger pulse. The 320F240 core can operate at a frequency of 20MHz, and its advanced structure enables almost all instructions to be completed within a single cycle of 50ns. Therefore, it has strong data processing capabilities and rich on-chip integrated peripherals; its event manager module has 12 comparison/PWM channels, which can easily implement the algorithm for generating trigger pulses. The control program flow is shown in Figure 2:

5 Simulation results

This power supply uses Matlab 6.0 as the simulation tool, and the model is built with modules in Simulink and Power system toolbox. Due to the use of a large number of power electronic modules, the simulation calculation is large, resulting in a long simulation time. Figure 3 shows the simulation output waveform from 0 to 0.2 seconds; it can be seen that the charging current is stable at about 0.7A after the transient process, and the 3000uF capacitor can be charged to 14KV within 60 seconds.

6 Conclusion

Since the output of this power supply is a large capacitive load, the control method of increasing the trigger pulse width by time and taking the output current and voltage values as references can meet the performance requirements.

References:

1. Modern Power Electronics Technology Foundation; Zhao Liangbing, ed.; Tsinghua University Press, 2000.

2. Soft Switching Technology of DC Switching Power Supply; Ruan Xinbo, Yan Yangguang, ed.; Science Press, 2000.

3. Detailed Explanation of MATLAB Simulation Application; Fan Yingle, Yang Shengtian, Li Yi, ed.; People's Posts and Telecommunications Press, 2001.

4. Fully Digital High-Frequency and High-Voltage Charging Power Supply; Xie Yonggang, Xu Zhixin, Zhong Heqing; High Voltage Technology, 2000.10.

5. DSP Controller and Its Application; Zhang Yun, Xie Liping, Xiong Hongyan, ed.; Machinery Industry Press, 2001.

Reference address：14KV—5KW high voltage capacitor charging power supply

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