Electromagnetic Field Analysis and Shielding Method of Underground Variable Frequency Power Cable

The transmission and radiation of underground variable frequency electromagnetic waves will seriously interfere with the operation of the power cable and its surrounding environment. At present, the test methods for power cables basically require the impedance of the test system to match the characteristic impedance of the cable. The defect is that the process of designing and making the impedance matching impedance network is relatively complex and requires high manufacturing accuracy. In order to solve these problems, this paper puts forward the electromagnetic field fast detection formula and electromagnetic field shielding method of underground variable frequency power cable. The research method of this paper is the principle of shielding electromagnetic field materials and the suppression principle of shielding layer for electromagnetic coupling. The function of the two principles is to study the reflection, absorption, and multiple reflection of electromagnetic waves and to study the cut-off frequency of the nonmagnetic shielding layer. These two principles guide the experiment. In this paper, the measurement formula of the shielding performance of mismatched cables is derived through experiments. The results show that the error of the measurement formula is no more than 8 dB. Then, through the experiment of restraining the interference of magnetic materials on the electromagnetic field, it is concluded that the magnetic field shielding performance can reach 20 dB. Then, through the performance test of electromagnetic field shielding materials, the shielding efficiency of metal fiber antiradiation materials is the largest, and the average efficiency reaches 76.4 dB.

Calculation of RMS Values for Variable Frequency Sinusoidal Signals, Using Phasors and Digital SAL and CAL Filters

The accurate measurement of RMS values of voltage and current is crucial for the monitoring and protection of power systems and in general for electrical power distribution systems. The authors in this paper have developed an algorithm to calculate the RMS value of sinusoidal signals of varying frequency, by applying phasors obtained from digital filters SAL and CAL. In conditions in which the frequency of the grid varies, a phase shift is presented in the phasor of the grid voltage which is used for the design of a regulator that allows to obtain accurate RMS voltage values. The choice of the SAL and CAL digital filters is due to their low computational requirement, so they can be implemented in general-purpose microcontrollers.

State Feedback Control Based Seamless Switch Control for Microgrid Inverter

With the wide application of distributed generations (DGs) and microgrids (MGs), the inverter control becomes a hot research topic. For the inverter control in MG applications, first, a complex variable state-feedback-based switch control frame is proposed. In the proposed control frame, the state feedback leads to a generalized control objective (GCO), and then the instantaneous voltage and current controls are designed based on the GCO. Finally, a complex variable frequency-locked loop (FLL) is adopted to realize the voltage and current reference computation. The control system is integrated by complex variables to alleviate the seamless switch. The effectiveness of the proposed control method is validated by experimental results.