Unified Power Flow Controller Based on Autotransformer Structure

Abstract

This paper proposes a new unified power flow controller (UPFC) topology. A single phase of them system with the proposed topology consists of an N:2 transformer with a center tap at the low-voltage side and a power converter module comprising full-and half-bridge converters. A three-phase system can be implemented with three devices. While the conventional UPFC topology uses two three-phase transformers, which are called series and parallel transformers, the proposed topology utilizes three single-phase transformers to implement a three-phase UPFC system. By using an autotransformer structure, the power rating of the transformers and the voltage rating of switches in the power converter module can be significantly decreased. As a result, it is possible to reduce the installation spaces and costs compared with the conventional UPFC topology. In addition, by adopting a full-and half-bridge converter structure, the proposed topology can be easily implemented with conventional power devices and control techniques. The techniques used to control the proposed topology are described in this paper. The results obtained from simulations and experiments verify the effectiveness of the proposed UPFC topology.

Nonlinear control strategy of single-phase unified power flow controller

“…Several simulation results show that additional robustness features are reached. Compared to the controllers previously cited, the new nonlinear controller enjoys several features including:  The present controller is designed for the single-phase UPFC system with reduced topology, this latter features less switches and a smaller number of gate drivers, compared to the Two-Leg Full-Bridge topology used in [6,18,19,20]. As a result, the present nonlinear controller is simpler to implement because it involves less control signals to generate and apply.…”

“…In [19], a new hybrid technique which combines the radial basis function (RBF) neural network with the sliding mode technique is proposed to design a UPFC system for power flow control of an electric power transmission system. In [20], a proportional resonant (PR) controller is used to generate switching signals for each leg of the input fullbridge converter; by synthesizing an appropriate injection voltage, the half-bridge inverter controls the power flow of the transmission line; in addition to simulation of system by MATLAB/Simulink, an experiment realization on the UPFC was carried out. In all the previous studies, the objective was controlling the power flow in the transmission systems between the power grids and the consumer loads in order to improve the quality of electrical energy; but note that the performances of the controllers which were proposed in [6,[16][17][18][19][20][21] were not quantified by the indication of the current THD and the voltage THD.…”

“… The performances of the proposed controller were quantified by calculation of the THD values of current and voltage. Such a study based in terms of THD current and voltage was missing in the all previous works [6,[16][17][18][19][20][21].  By using a rigorous theoretical analysis, the control objectives (i.e.…”

“…PFC, compensation of voltage perturbations and DC voltage regulation) are actually achieved. Such a formal analysis was missing in the all previous works [6,[16][17][18][19][20][21]. This paper organized as follows: Section 2 is devoted to the description and modeling of the singlephase UPFC system.…”

“…Let us consider the following Lyapunov function. ( 2) V V z  (22) Using (20), the time-derivative of 3 is given by: (23) To ensure that the ( 2 , 3 )-system to be globally asymptotically stable, it is sufficient to choose the control law so that which, due to (23), amounts to ensuring that:…”