With analyzing the traditional characteristics of double tuned filter, a novel three-tuned filter for power system is proposed in the paper. The filter is equivalent to three single tuned filters. The algorithm for determining the filter's parameters is presented. A three-tuned filter for a 110 kV power grid is designed, simulated and tested. The results show that the filter can filter three different given frequency harmonics, and it has better performance than three single-tuned filters in filtering harmonics, low power loss, low space occupation, low price, only one reactor subjected to power line-power voltage and one switchgear needed.

The asymmetric faults often cause the power grid current imbalance and power grid oscillation, which brings great instability risk to the power grid. To address this problem, this paper presented a modeling and parameter optimization method of grid-connected photovoltaic (PV) systems, considering the low voltage ride-through (LVRT) control. The harmonics of the grid current under asymmetric faults were analyzed based on the negative-sequence voltage feedforward control method. The notch filter was added to the voltage loop to filter out the harmonic components of the DC bus voltage and reduce the harmonic contents of the given grid current value. The proportional resonant (PR) controller was added to the current loop. The combination of these two components could reduce the 3rd, 5th, and 7th harmonics of the grid current and the output power fluctuation. Then, the parameters of the inverter controller were identified by the adaptive differential evolution (ADE) algorithm based on the sensitivity analysis. The effectiveness of the proposed method was compared with two other strategies under the asymmetric grid faults. The suppression of DC bus voltage fluctuation, power fluctuation, and low-order harmonics of the grid current all had better results, ensuring the safe and stable operation of the PV plant under grid faults.

This paper presents an engineering design method for output filter in parallel active power filters. LCR filter with resonance attenuation characteristic is applied. The special requirements of output filter are analyzed in parallel active power filter. The proposed method firstly builds multi-objective function considering requirements of switching harmonic attenuation, output capability and power loss. Then, fuzzy optimization is used to obtain optimal parameters of output filter. Therefore, the comprehensive performance of parallel active power filter is enhanced, including compensation capability and power loss. The simulation and experimental results verify the feasibility of the proposed method.

Power grid fault location system using voltage traveling wave has been developed successfully by the authors. It includes traveling wave sensor, fault locator, and fault calculation center. Outputs of the sensors are applied to record the fault traveling wave arrived time with global position system (GPS) receiver in fault locator that is installed in every power station. The recorded times are then sent to fault calculation center. And the fault calculation center calculates the fault position. The fault calculation center communicates with fault locators in star model. Software for the calculation center and fault locator are designed in Delphi Language and presented in the paper, including display, human machine interface (HMI), communication, fault calculation, fault reporting, data base. The software is applied in a real power system for fault location. Test results show that the software has good performance and high reliability.