| In recent years, with the continuous expansion of city scale, the scale of the low-voltage distribution network of our country city is expending year by year. The traditional overhead line is gradually replaced by the cable line. So that the line to ground capacitance increases rapidly and the neutral grounding mode changes accordingly. The necessity of arc-extinguish coil installation, its capacity selection and accurate tracking compensation are all depending on the accurate measurement of capacitive current. Therefore, it is of great theoretical and practical significance to develop capacitive current measuring device for distribution network.In this paper, it made the analysis of the neutral grounding mode of Dongying regional distribution network and developed the application analysis of signal injection method in measurement of capacitance current in terminal area distribution network. Through the stability analysis, relative error analysis and simulation experiments, the applicability, advantages and limitations of several common signal injection methods are compared and the variable frequency signal injection method was determine as the core approach. The capacitance current measurement device based on the variable frequency signal injection method is essentially a signal generator. The DSP combines with the FPGA as the controller of the design and the SPWM pulse width modulation is used as the H-bridge inverter control signal source. The current hysteresis control is used to achieve the closed-loop control of the inverter. Simulated and verified the variable frequency signal source by the MATLAB software and designed the hardware and software of the device. The simulation experiment platform of power grid is set up and the variable frequency signal source is simulated. The test results show that the output of the device is stable and reliable with a certain unbalanced voltage in the power grid. It has a high precision and a certain degree of practicality. |
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