Haiping Yin

On Active/Reactive Power Modulation of DFIG-Based Wind Generation for Interarea Oscillation Damping

In this paper, the interactions of the torsional dynamics of the wind turbines and power modulation for oscillations in DFIG-based wind generators are investigated. One major concern of active power modulation is its interaction with wind turbines torsional dynamics. A study case with wind turbine torsional dynamics modeled is derived from our earlier work. Both active power modulation and reactive power modulation controls are developed in this paper. The paper successfully demonstrates the presence of interaction between active power modulation and torsional dynamics and the absence of such interaction in the case of reactive power modulation. Linear system analysis and root loci approach are employed to demonstrate such interaction. Simulation results in MATLAB/Simulink further verifies the analysis. The major contribution of this paper is: 1) the demonstration of the potential disadvantage of wind generations active power modulation; and 2) the identification of reactive power modulation in wind generation as an alternative for interarea oscillation damping.

Control of DFIG for rotor current harmonics elimination

Unbalanced stator conditions cause rotor current harmonics and torque pulsations in Doubly-Fed Induction Generators (DFIG) which are used widely in wind energy systems. From a hardware perspective, current control techniques to minimize the rotor current harmonics include rotor-side converter injected voltage compensation and grid-side converter compensation. From a software perspective, the current controllers either adopt synchronous reference frame for controller design or adopt positive synchronous (qd+) negative synchronous reference frames (qd−) to decompose the harmonics in rotor currents and control them separately. This paper develops a proportional resonance (PR) control strategy in the stationary reference frame (αβ) to minimize rotor current harmonics and torque pulsations. The main advantages of the proposed method are (i) only one transformation (abc/αβ) is required and (ii) harmonic filters are not required. The proposed control strategy is compared with the proportional integral (PI) control strategyin qd+ and qd− and the proportional integral and resonant (PIR) control strategy in qd+. Simulations performed in Matlab/Simulink are presented to illustrate the effectiveness of the proposed control strategy.

Reactive power modulation for inter-area oscillation damping of DFIG-based wind generation

Oscillation damping via variable speed wind generators have been addressed in literature. Among the techniques, active power modulation has been studied. However, active power is closely related with electromagnetic torque. Modulating active power can introduce oscillations in the torque. This is undesired. The objective of this paper is to study an alternative technique - reactive power modulation for inter-area oscillation damping. A two-area four-machine power system with doubly-fed induction generator (DFIG)-based wind farm is modeled in MATLAB/Simulink. Vector control for rotor-side converter (RSC) of DFIG is modeled. A control scheme based on reactive power modulation for inter-area oscillation damping is proposed. Simulation results in MATLAB/Simulink demonstrate the effectiveness of the control technique.

Negative sequence compensation techniques of DFIG-based wind energy systems under unbalanced grid conditions

This paper presents analysis and control techniques for a doubly-fed induction generator (DFIG) used in wind energy systems under unbalanced grid conditions. The rotor currents and electromagnetic torque of the DFIG under unbalanced conditions are first analyzed. Negative sequence circuit models are investigated. Control strategies implementing negative sequence compensation from either the grid-side converter (GSC) or the rotor-side converter (RSC) are developed. The control objective of the GSC compensation is to provide the negative sequence currents for the grid to keep the stator currents free of negative sequence component. The control objective of the RSC compensation is to eliminate the rotor current harmonics. The main contribution of the paper is i) the analysis of the root cause of the high frequency harmonics in rotor currents and the electromagnetic torque and, ii) the comparison of the two control techniques frequently used in research. Matlab/Simulink tests for a 2MW DFIG are performed to confirm the analysis.

Fast Power Routing Through HVDC

The objective of this paper is to investigate the fast power-routing capability of line current commutating (LCC)-HVDC. Such capability is most desired in future grids with high penetration of renewable energy sources (e.g., wind and solar). The technology presented in this paper replaces the traditional LCC-HVDC rectifier power order control by an ac voltage-mode control. This technology enables the HVDC rectifier ac bus to act as an infinite bus and absorb fluctuating wind power. A study system consisting of an ac system, an LCC-HVDC, and a doubly fed induction generator-based wind farm is built in Matlab/SimPowersystems. Simulation studies are carried out to demonstrate the proposed HVDC rectifier control in routing fluctuating wind power and load change. Parameters of the proposed voltage-mode control are investigated to show their impact on HVDC power routing and ac fault recovery.

Modeling and control of DFIG-based large offshore wind farm with HVDC-link integration

This paper presents an analysis and a power coordination technique for a Doubly-Fed Induction Generator (DFIG)-based wind farm with HVDC-link integration. Control and operation of both rotor-side converter (RSC) and grid-side converter (GSC) are analyzed. The RSC control loop tracks maximum wind power and controls stator flux linkage. The GSC control loop maintains stator terminal voltage and dc-link voltage between the RSC and the GSC. Line-commutated converter (LCC)-based HVDC transmission system is used for grid integration. The main control philosophy of the HVDC link is that firing angle of the rectifier is adjusted base on bus voltage magnitude. While the wind speed changes, through the rectifier control loop, dc voltage at the sending end of HVDC-link will vary with the firing angle, thus power balance of the AC and DC sides is achieved. Matlab/Simulink tests for a 2 MW DFIG with simplified HVDC-link model are performed to confirm the analysis and operation principle.

PMU data-based fault location techniques

Accurate fault location promotes the reliability of the power system. This paper reviews various fault location techniques for transmission lines and presents PMU-based fault location methods. In 1950, the traveling waves-based fault location was first proposed. It calculates the fault location by measuring the relative time of the traveling wave arrives at the ends of transmission line. However, the high sampling rate limits its application. Then, fault location based on impedance was also developed. This method measures the voltage and current of one or two ends of the transmission line to calculate the fault impedance. Thus, the fault location could be known if the impedance of the transmission line is uniform. Whats more, distributed parameter transmission line model based method is also presented. In this paper, two-ended data are assumed to be measured by PMUs. Three-phase and one-phase transmission lines with two sources are tested in PSCAD. Simulation results of fault location methods based on negative-sequence impedance and distributed parameter transmission line models are also given.

Fast power routing through HVDC

The objective of this paper is to investigate the fast power-routing capability of line current commutating (LCC)-HVDC. Such capability is most desired in future grids with high penetration of renewable energy sources (e.g., wind and solar). The technology presented in this paper replaces the traditional LCC-HVDC rectifier power order control by an ac voltage-mode control. This technology enables the HVDC rectifier ac bus to act as an infinite bus and absorb fluctuating wind power. A study system consisting of an ac system, an LCC-HVDC, and a doubly fed induction generator-based wind farm is built in Matlab/SimPowersystems. Simulation studies are carried out to demonstrate the proposed HVDC rectifier control in routing fluctuating wind power and load change. Parameters of the proposed voltage-mode control are investigated to show their impact on HVDC power routing and ac fault recovery.