The grid impedance is time varying due to the changing structure of the power system configuration and it can have a considerable influence on the control and stability of grid connected converters. This paper presents an online grid impedance estimation method using the output switching current ripple of a SVPWM based grid connected converter. The proposed impedance estimation method is derived from the discretised system model using two consecutive samples within the switching period. The estimated impedance is used for islanding detection and online current controller parameter adaptation. Theoretical analysis and MATLAB simulation results are presented to verify the proposed method. The effectiveness of the grid impedance estimator is validated using experimental results.
The grid impedance is time varying due to the changing structure of the power system configuration and it can have a considerable influence on the control and stability of grid connected converters. This paper presents an online grid impedance estimation method using the output switching current ripple of a SVPWM based grid connected converter. The proposed impedance estimation method is derived from the discretised system model using two consecutive samples within the switching period. The estimated impedance is used for islanding detection and online current controller parameter adaptation. Theoretical analysis and MATLAB simulation results are presented to verify the proposed method. The effectiveness of the grid impedance estimator is validated using experimental results.
Abstract-A method for hybrid active damping in power converters connected to a weak grid using an LCL filter is proposed. It uses feedback of the grid current and capacitor voltage and is derived as an equivalent to the capacitor current feedback active damping method. A co-design procedure for the grid current controller with the proposed hybrid active damping method is presented. The robustness, system bandwidth and harmonic rejection are studied. The proposed method is applied to a single grid connected converter with variable grid inductance to investigate its ability to damp different system resonance frequencies and its effectiveness is verified via frequency domain analysis and time domain simulation.
Abstract-Call admission control (CAC) is essential to guarantee the signal quality in CDMA systems. Signal-tointerference-and-noise ratio (SINR) is used as a criterion for user admission by comparing the SINR with a predefined threshold value (SINR th ). The choice of the SINR th value is restricted by two opposing factors: the signal quality and the network utilization. Setting SINR th at high value is desirable to increase the signal quality. However, SINR th shouldn't exceed a certain limit to keep the blocking probability (P b ) below a maximum value. In this paper, we derive an upper bound of SINR th (SINR th-ub ) for multi-class CDMA systems with imperfect power control. SINR th-ub of class i (SINR th-ub (i), i=1, 2,…., L) is determined by finding the relationship between the blocking probability of all classes and SINR th (i). Then, SINR thub (i) is determined as the highest value of SINR th (i) that keeps the blocking probability of all classes below the corresponding maximum values.
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