New control approach for capacitor supported DSTATCOM in three-phase four wire distribution system under non-ideal supply voltage conditions based on synchronous reference frame theory

A large number of single-phase linear and non-linear loads may be supplied from three phase ac mains with neutral conductor. They cause excessive neutral current, harmonics and reactive power burden and unbalance. A four wire DSTATCOM (distribution static compensator) is used for neutral current compensation along with reactive power compensation, harmonics elimination and load balancing. A novel control approach is proposed for the control of four wire DSTATCOM under non-ideal supply voltage conditions. A four-leg voltage-source converter (VSC) with a dc capacitor is used as a four wire DSTATCOM. The proposed control approach is based on synchronous reference frame (SRF) theory and an indirect current control technique. The switching signals for the voltage-source converter (VSC) of the DSTATCOM are derived from the estimated reference supply currents. The load balancing, harmonics elimination and the neutral current compensation are demonstrated along with unity power factor (UPF) and zero voltage regulation (ZVR) modes of operation. Simulation results based on MATLAB software with its Simulink and power system blockset (PSB) toolboxes are presented to validate the control strategy. The DSTATCOM is able to maintain the self-supported dc bus under various disturbances.     

Comparison of control strategies for DSTATCOM in three-phase,four-wire distribution system for power quality improvement under various source voltage and load conditions

This paper presents comparison of three different control strategies to generate reference current components for Distribution Static Compensator (DSTATCOM). Reference currents are tracked by a three-phase voltage source converter in a hysteresis band control scheme. These methods are instantaneous reactive power (IRP) theory, symmetrical component (SC) theory and an improved instantaneous active and reactive current component (IARCC) theory. The performance of three methods has been evaluated under various source voltage and load conditions with new IEEE Standard 1459 power definitions. A comparative study of their performance in terms of rms value of source current, Total Harmonic Distortion (THD), supply power factor and compensator ratings is also presented. A three-phase, four-wire distribution system supplying linear as well as non-linear load is considered for simulation study which is carried out using MATLAB/SIMULINK software. Under balanced and sinusoidal source voltage conditions, all three control strategies similar performance while an improved IARCC theory outperforms, particularly, under unbalanced and distorted source voltage conditions.     

A correlation based method for discrimination between inrush and short circuit currents in differential protection of power transformer using Discrete Wavelet Transform: Theory,simulation and experimental validation

This paper presents a new method for discrimination between magnetic inrush current and internal fault current in the differential protection of power transformer. The proposed method is based on the Wavelet Transform and correlation coefficient. In this study Discrete Wavelet Transform is used to describe the current signal in terms of different time and frequency components. In the proposed method, the energy signals of these components are employed. In the proposed method, a statistical parameter known as correlation coefficient is used to establish a criterion for the proposed discriminative algorithm. The correlation coefficient is used for express the relationship between wavelet coefficients energy at different scales of the signal resolution. Then pattern of these relations is utilized as a measure to discriminate the inrush current from fault current. For investigation the accuracy of the proposed algorithm different cases of inrush and internal fault currents is simulated by PSCAD/EMTDC software. Also, the proposed method is tested by the gathered data from experimental test at the laboratory. Current signals obtained from the simulation as well as the results obtained from the experimental test are employed by the proposed discriminative algorithm. Analysis of the simulation and experimental results show that the proposed method accurately identifies inrush and fault currents in the distance of the power transformer protection in a time period less than quarter of power frequency cycle. In addition to the sensitivity and high reliability, the proposed method has low computation work and does not required determining the threshold for each new power system.