Volume 12, Issue 6

Saturation problem in steel core Current Transformers (CTs) causes dreadful effects in protection systems as true replica of the primary current is not always reflected in CT secondary side under abnormal operating conditions. This is why detection and production of exact replica of primary current in the CT secondary side is very crucial. This paper presents a discrete wavelet transform based application using 'Daubechies3’ as mother wavelet for the detection of saturation. The compensation of saturated signal is done by Gregory Newton's Backward Interpolation (GNBI). The whole scheme of detection of CT saturation and compensation of saturated CT secondary current has been successfully tested on various saturated signals simulated in MATLAB/SIMULINK with various case studies. Finally, the scheme is validated in real time using DS1104 controller board of dSPACE. The results obtained are very encouraging.

This paper presents a novel unified dynamic model and control strategy to improve the power quality for VSC based high voltage direct current transmission system (VSC-HVDC) under unbalanced grid conditions. The unified models present the dynamic behavior of VSC-HVDC in the unique positive synchronously rotating reference (dq-p) frame with respect to both the positive- and negative-sequence components. Based on the unified model, a strategy to either eliminate the dc-link ripple or achieve the balanced currents, along with a rather low level harmonics in each grid is introduced by resorting to the resonant integrator and filter based scheme in the two cascaded control loops. The resonant integrator and filter scheme enables effective control of the positive- and negative-sequence currents, and avoid the sequence component decomposition. The simulation studies in PSCAD/EMTDC verify the improved performance of VSC-HVDC system regarding the power quality and the ride-through capability.

This paper presents a smoothing method of output power by using pitch angle control, inertia of a wind turbine and DC-Link voltage control of a wind energy conversion system (WECS) using a permanent magnet synchronous generator (PMSG). The output power fluctuations in low and high frequency domains are smoothed by the pitch angle control of the WECS and the DC-Link voltage control, respectively. The remaining frequency, i.e., middle frequency is smoothed by the inertia of the wind turbine. The generator-side converter controls the generator torque of PMSG while the grid-side inverter controls the DC-Link voltage and grid voltage. From the proposed method, the generator torque is smoothed and kinetic energy generated by the inertia of the wind turbine is used to smooth the power fluctuations of the PMSG and wind turbine blade stress is mitigated as the pitch action in high frequency domain is reduced. Due to the DC-Link voltage in this paper by an appropriate operating region, the output power smoothing is achieved with stability and low cost. The effectiveness of the proposed method is validated by numerical simulations.