In this paper, the fractional-order modeling and analysis of a three-phase voltage source PWM rectifier (VSR) are researched considering the fractional-order characteristics of actual inductors and capacitors. While the Caputo fractional calculus operator is used to describe the fractional-order characteristics of an inductor and a capacitor, the fractional-order model of a three-phase VSR is established in the threephase static coordinate system. With the coordinate transformation, the fractional-order model is expressed in the two-phase static coordinate system and in the synchronous rotation coordinate system, respectively. Simulation results verify the effectiveness of the established models, and indicate that the fractional-order models can describe the operating characteristics of a three-phase VSR more accurately. Besides, compared with the traditional integer-order three-phase VSRs, the three-phase VSRs which contain the fractional-order inductors and the fractional-order capacitor can present better static and dynamic performance indexes (such as smaller overshoot and shorter regulation time) by appropriately selecting the orders of the inductors and the capacitor.
In this paper, the nonlinear U model with time-varying coefficients is investigated and the transformation of the nonlinear model is accomplished by the Newton iterative algorithm. Based on the nonlinear U model, a control algorithm with cerebellar model articulation controller and proportional derivative (PD) in parallel is proposed. The algorithm learns online through a neural network while optimizing the output of the PD, which ultimately enables the actual output of the system to track up to the desired output. Considering that the nonlinear object has the characteristic of rapid change with time, the article improves the PD algorithm to nonlinear PD control algorithm to complete the design of the system. The algorithm automatically adjusts the weights according to the error magnitude to complete the controller parameter adjustment, thus reducing the error of the system. The simulation results show that the nonlinear PD algorithm is better than the PD algorithm, meanwhile, the tracking speed and control precision of the system are improved.
This paper proposes a novel multi-index nonlinear robust control (MNRC) approach for multi-machine power systems. The MNRC approach combines multi-index nonlinear control with the H ∞ control theory. With the multi-index nonlinear control, which selects the output functions as arithmetic combination of state variables, multiple performance indices of the controlled system can be achieved simultaneously in the nonlinear control framework. The H ∞ control is able to ensure that the system possess the desired robust performance during disturbance. Then, excitation and steam-valving coordinated robust controllers are developed based on the MNRC approach for multi-machine power systems. The effectiveness of the proposed robust controller is evaluated by a six-machine power system simulation. Simulation results show that the expected dynamic and steady-state performances of power system can be achieved with the MNRC approach. Meanwhile, it is able to achieve the prescribed system performance despite the presence of disturbances.
Non-member Yejie Tian, Non-member The problem of shafting torsional vibrations has been increasingly emerging due to the increasing capacity of turbo-generator and the complexity of power grid. Therefore, how to reduce the torsional vibration of the turbo-generator shaft and improve the stability of the power system has become the focus of our research. First, in order to solve the problem and alleviate the torsional vibrations of turbo-generator shafts, this paper proposed a new shafting structure model of Double-ended Driving and Dual-Excited Turbo-Generator set (DDDETG). A static excitation mode is used for the excitation of the DDDETG and the mechanical power is supplied symmetrically and synchronously from both ends of the generator rotor. Then, in order to improve the output characteristic of the generator and further suppress the torsional vibrations of the turbo-generator shafts, combined with the nonlinear control design method of partial feedback linearization, a Multi-Index Nonlinear Coordinated Control (MINCC) strategy for the double-ended driving and dual-excited turbo-generator is proposed to ensure good dynamic and static state performances of each state in the system. Finally, the simulation results on a single-machine infinite bus system demonstrate the effectiveness of the proposed control strategy. In addition, this paper compares the performance of DDDETG and the traditional Single-ended Drive and Single-Excited Turbo Generator (SDSETG), the simulation results show that the restraint effect of the DDDETG structure on shafting torsional vibrations is more obvious under the proposed control strategy.
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