quasi-PR Controller Research Articles

An Optimal Integrated Control Scheme for Permanent Magnet Synchronous Generator-Based Wind Turbines under Asymmetrical Grid Fault Conditions

In recent years, the increasing penetration level of wind energy into power systems has brought new issues and challenges. One of the main concerns is the issue of dynamic response capability during outer disturbance conditions, especially the fault-tolerance capability during asymmetrical faults. In order to improve the fault-tolerance and dynamic response capability under asymmetrical grid fault conditions, an optimal integrated control scheme for the grid-side voltage-source converter (VSC) of direct-driven permanent magnet synchronous generator (PMSG)-based wind turbine systems is proposed in this paper. The optimal control strategy includes a main controller and an additional controller. In the main controller, a double-loop controller based on differential flatness-based theory is designed for grid-side VSC. Two parts are involved in the design process of the flatness-based controller: the reference trajectories generation of flatness output and the implementation of the controller. In the additional control aspect, an auxiliary second harmonic compensation control loop based on an improved calculation method for grid-side instantaneous transmission power is designed by the quasi proportional resonant (Quasi-PR) control principle, which is able to simultaneously restrain the second harmonic components in active power and reactive power injected into the grid without the respective calculation for current control references. Moreover, to reduce the DC-link overvoltage during grid faults, the mathematical model of DC-link voltage is analyzed and a feedforward modified control factor is added to the traditional DC voltage control loop in grid-side VSC. The effectiveness of the optimal control scheme is verified in PSCAD/EMTDC simulation software.

Research on the Single Phase Grid-Connected Inverter System of Small Wind Power

The main circuit structure of single-phase wind power system, grid inverter model with modeling, and the design of the filters are introduced. Comparing two control strateies between several common control strategies with using Matlab/simulation tools. The results show that quasi-PR control has better performance.

Simplified Controller Design Method for Digitally Controlled LCL-Type PWM Converter with Multi-resonant Quasi-PR Controller and Capacitor-Current-Feedback Active Damping

To track the sinusoidal current under stationary frame and suppress the effects of low-order grid harmonics, the multi-resonant quasi-proportional plus resonant (PR) controller has been extensively used for digitally controlled LCL-type pulse-width modulation (PWM) converters with capacitor?current?feedback active damping. However, designing the controller is difficult because of its high order and large number of parameters. Moreover, the computation and PWM delays of the digitally controlled system significantly affect damping performance. In this study, the delay effect is analyzed by using the Nyquist diagrams and the system stability constraint condition can be obtained based on the Nyquist stability criterion. Moreover, impact analysis of the control parameters on the current loop performance, that is, steady-state error and stability margin, identifies that different control parameters play different decisive roles in current loop performance. Based on the analysis, a simplified controller design method based on the system specifications is proposed. Following the method, two design examples are given, and the experimental results verify the practicability and feasibility of the proposed design method.

Research on Control Strategy of PV MPPT and Grid-Connected Single Phase Converter Based on Two Stage Topology

This paper studied the control strategy of single-phase two-stage grid-connected photovoltaic generation system. The two-stage topology includes the boost converter and single phase inverter. The function of maximum power point tracking (MPPT) is achieved in the boost circuit by IC (Increment Conductance) method. The inverter circuit adopted the double-closed loop control, a DC voltage outer loop control for power balance with PI correction and an AC current inner loop control for feedback designed to ensure the current quality and stabilize the DC voltage. The inner loop used the novel quasi-Proportional-Resonant (PR) controller, which has a better steady tracking characteristics and stronger anti-interference ability to the disturbance. Finally, a simulation system is built with Matlab/Simulink in this paper to verify the validity of the MPPT algorithm and the quasi-PR control strategy.Keywords：Photovoltaic Generation System;Maximum Power Point Tracking; Grid-connected Inverter; quasi-Proportional-Resonant (PR) controller