Li Lanfang

Repetitive control implementation with frequency adaptive algorithm for shunt active power filter

Shunt active power filter (APF), as parallel part of unified power quality modulation (UPQC), has been proved as a flexible solution for compensating the harmonic distortion caused by nonlinear loads in power distribution power systems. Digital repetitive control can achieve zero steady-state tracking error of any periodic signal under the sampling points within one repetitive cycle that must be a specific integer. However, the compensation performances of the APF would be degradation when the grid frequency varies. In this paper, an improved repetitive control scheme with frequency adaptive capability is presented to track any periodic signal with variable grid frequency, and then the variable delay items caused by time-varying grid frequency are approximated with Pade approximants. Additionally, the stability criterion of proposed repetitive control scheme is given. A three-phase shunt APF experimental platform with proposed repetitive control scheme is built in our laboratory. Simulation and experimental results demonstrate the effectiveness of the proposed repetitive control scheme.

Real-time simulation and parameter optimization for SVC control tragedy of XiZang grid

Since Qingzang HVDC system put into operation in 2011, higher requirements for voltage stability in Xizang grid must be taken into account. It plans to install several SVC devices at three 220 kV stations which include Duodi, Naiqiong and QuGe, in order to improve the voltage quality of Xizang Grid and the transmission capacity of QingZang HVDC system. To optimize and validate the control tragedy of these SVCs before their installation, a real-time digital/analog hybrid simulation platform is setup by HYPERSIM. This platform is composed of a digital model which includes detail 220 kV and 110 kV network of XiZang grid, an analog HVDC controller for Qingzang HVDC system, and all the analog SVC controllers. It includes two types of SVC devices for the real project, one is TCR+SC, and another is TSC. Based on the simulation platform, the SVC control tragedies of these two types are validated respectively. The simulation results show: through adding SVC devices at the 220 kV stations, the Xizang grid has better voltage recover characteristic after short-circuit fault. It can draw a conclusion that the voltage control tragedy used in this real project has favorable control characteristic for the voltage stability of Xizang Grid.

Application of DSOGI-SPLL algorithm on shunt active power filter under unbalanced and distorted voltages

On the application of a shunt active power filter (SAPF), the detection accuracy of harmonics is a vital factor to judge the performance of the SAPF, which is indeed strongly depended on the veracity of software phase-locked loop (SPLL). However, phase jump, frequency variation and harmonic accompanied with the voltage sags usually impact the dynamic response and accuracy of SPLL. In this paper, a detailed study of Double Second Order Generalized Integrator SPLL (DSOGI-SPLL) and simulation are performed. Then, a three phase four wire SAPF simulation model based on DSOGI-SPLL was built using MATLAB/SIMULINK programs and a 100A three-phase four-wire SAPF prototype is tested, which proved the validity and correctness of DSOGI-SPLL on the test platform.

Research on an improved fuzzy detecting algorithm of harmonic and reactive-power signals for the shunt APF

The harmonic and reactive current detection and analysis is a prerequisite to achieve the control of power quality, the accurate detection of harmonic and reactive current can provide a good basis for harmonic control. this paper proposes an improved harmonic and reactive-power current detection technique based on the fuzzy controller method combined with particle swarm optimization (PSO) for the APF, the PSO can enlarge the value range of the adjustment factor of signal parameters in the Fuzzy algorithm, the harmonic and reactive-power components can be detected fast and accurately. The proposed method has some advantages such as: This method omits the vector transform and low-pass filter, and the hardware cost of this method is low for no PLL circuit. Simulation and experimental results are utilized to prove that the proposed algorithm is simple and effective.