Design of self-integrating capacitor voltage divider for measurement

Author： GOZ Electric Time：2024-10-27 09:36:55 Read：20

In order to study the steepening mechanism of the pulse front edge of the ferrite transmission line, six coupled self-integrating capacitor voltage dividers were developed to measure the voltage waveform at different positions of the transmission line, so as to analyze the steepening process of the pulse front edge. Firstly, the equivalent circuit model of the capacitor voltage divider was established by Pspice, and the influence of the coaxial signal cable matching method and the stray inductance of the low-voltage arm compensation capacitor on the measurement output of the capacitor voltage divider was analyzed from the time domain and frequency domain. It was proposed to use a PCB coaxial structure with multiple capacitors in parallel to reduce the influence of its stray inductance on the high-frequency oscillation of the pulse. Then, a coupled capacitor voltage divider with low stray inductance was designed according to the transmission line structure. The high and low voltage arm capacitance values were calculated by Comsol simulation and the theoretical voltage divider ratio was derived. The output signal of the capacitor voltage divider working in D-dot mode and self-integration mode was experimentally tested, and the voltage divider ratio and response time of the voltage divider were calibrated. The results show that the measured voltage divider ratio of the developed capacitor voltage divider is close to the theoretical value, and the response time is about 2.1ns. The simultaneous measurement of pulse voltages at different positions of the 6-level ferrite transmission line is realized.

Keywords: ferrite transmission line; pulse voltage; capacitor voltage divider; impedance matching; voltage divider ratio

Experimental verification

After installation, the capacitor voltage divider needs to be calibrated one by one. The experiment uses the Polaris PVM-6 high-voltage probe and the capacitor voltage divider for simultaneous measurement. In order to reduce the delay caused by different measurement cable lengths, the cable length is 9m. The oscilloscope model for measurement and recording is Tektronix DPO4054B, with a bandwidth of 500MHz and a sampling rate of 5 GS/s, which meets the response requirements of fast pulse testing

1. Working mode

The verification uses the output pulse calibration at the end of the transmission line, with an amplitude of about 120kV, and a leading edge and pulse width of 20ns and 200ns respectively. After adding the compensation capacitor, the capacitor voltage divider works in the self-integration mode. The simulation and experimental waveforms of PVM-6 and the capacitor voltage divider in D-dot mode and self-integration mode are shown in the figure below.

As can be seen from the figure, the voltage divider works in two different modes. In the D-dot mode, the voltage divider outputs the change rate of the voltage to be measured, and in the self-integration mode, the voltage to be measured is restored and the voltage amplitude and the front edge measurement have good consistency.

2. Voltage divider ratio calibration

The transmission line pulse output is adjusted by adjusting the DC voltage in the primary pulse source. 30 sets of experimental waveforms are measured at different voltage levels. The average value of the pulse peak value output by PVM-6 and the self-integration capacitor voltage divider is calculated, and the voltage divider ratio is calculated accordingly.

3. Response time calibration

For fast front edge pulse voltage signals, the response speed of the capacitor voltage divider must be sensitive enough to output the voltage waveform well. Therefore, this paper extracts data from the voltage waveform under multiple experiments under the same conditions to calibrate the voltage divider response time.

Conclusion

Based on the test requirements of the experimental platform for the steepening of the pulse front of ferrite transmission lines, a pulse high-voltage capacitor voltage divider was developed. The parameters of the capacitor voltage divider were determined through theoretical calculation and simulation. The working mode of the capacitor voltage divider under different integration times was verified experimentally. The voltage divider ratio and response time of the voltage divider were calibrated and calculated. The voltage divider ratio was 43 005 and the response time was 2.1ns. The pulse voltage at different positions of the 6-level transmission line can be measured simultaneously, and the high-voltage pulse signal can be accurately restored. It has been applied to the study of the steepening mechanism of the pulse front of ferrite transmission lines.