Reactive Power Control Mode Research Articles

Reactive power control strategy for a wind farm with DFIG

Reactive power control strategy for a wind farm with a doubly fed induction generator (DFIG) is investigated. Under stator flux-oriented (SFO) vector control, the real power of the DFIG is controlled by the q-axis rotor current Iqr and the reactive power is mainly affected by the d-axis rotor current Idr. To examine the effect of Idr on stator reactive power Qs and rotor reactive power Qr, the DFIG is operated under five different operating modes, i.e, the maximum Qs absorption mode, the rotor unity power factor mode, the minimum DFIG loss mode, the stator unity power factor mode, and the maximum Qs generation mode. In pervious works, stator resistance Rs was usually neglected in deriving the d-axis rotor currents Idr for different DFIG reactive power operating modes. In the present work, an iterative algorithm is presented to compute the d-axis rotor currents Idr for the five reactive power control modes. To demonstrate the effectiveness of the proposed iterative algorithm, the rotor current, rotor voltage, stator current, real power and reactive power of a 2.5 MW DFIG operated under the five different operating modes are computed.

Impact Study of PMSG-Based Wind Power Penetration on Power System Transient Stability Using EEAC Theory

Wind turbines with direct-driven permanent magnet synchronous generators (PMSGs) are widely used in wind power generation. According to the dynamic characteristics of PMSGs, an impact analysis of PMSG-based wind power penetration on the transient stability of multi-machine power systems is carried out in this paper based on the theory of extended equal area criterion (EEAC). Considering the most severe PMSG integration situation, the changes in the system’s equivalent power-angle relationships after integrating PMSGs are studied in detail. The system’s equivalent mechanical input power and the fault period electrical output power curves are found to be mainly affected. The analysis demonstrates that the integration of PMSGs can cause either detrimental or beneficial effects on the system transient stability. It is determined by several factors, including the selection of the synchronous generators used to balance wind power, the reactive power control mode of PMSGs and the wind power penetration level. Two different simulation systems are also adopted to verify the analysis results.

A Fuzzy Logic Controller for Autonomous Operation of a Voltage Source Converter-Based Distributed Generation System

This paper presents a fuzzy logic controller (FLC) for autonomous (islanded) operation of an electronically interfaced distributed generation unit and its load. In the grid-connected mode, the voltage-sourced converter is operated in the active and reactive power (PQ) control mode, where a conventional control scheme is used to control the active and reactive power exchange with the grid. In the islanded mode, the proposed FLC is used to control the voltage of the islanded system despite the load variability and uncertainties. In addition, this paper also presents the use of the black-box nonlinear optimization technique to tune the parameters of the membership functions of the FLC in order to achieve optimal performance. The salient features of the proposed FLC are: 1) efficient to deal with the nonlinear systems; 2) design does not depend on the mathematical model of the system; and 3) less sensitive to the parameters variation than the conventional controllers. The frequency of the islanded system is dictated through the use of an internal oscillator. The effectiveness of the proposed FLC in controlling the voltage of the islanded system, irrespective of the load variability, is extensively validated based on simulation studies in the PSCAD/EMTDC environment. Moreover, the paper highlights the superiority of the proposed FLC over the conventional proportional-integral controllers through comparing the transient responses of the system based on both controllers.

Impact of Distributed Wind Generators Reactive Power Behavior on Flicker Severity

When wind farms are connected to weak distribution networks, significant flicker emission can be expected, and it might not comply with the enforced grid code limits. This paper investigates and analyzes the impact of the possible wind generator reactive power control modes on the produced flicker levels. A frequency-selective reactive power control scheme is also proposed that makes it possible to mitigate the wind generator flicker emission under any reactive power exchange mode of the machine with the grid while respecting the grid code power factor restrictions. A realistic short-term wind profile is used and simulations are conducted on a 2 MW DFIG unit. Flicker measurement is carried out per IEC Standard 61000-4-15.

Analysis of Stability Limitations of a VSC-HVDC Link Using Power-Synchronization Control

In this paper, the stability limitations are analyzed for a voltage-source converter (VSC) based high-voltage direct-current (HVDC) link using power-synchronization control for two feasible operation modes: alternating-voltage control and reactive-power control. As a comparison, the analysis has been done by the phasor approach and the space-vector approach. While the phasor approach is straightforward to apply and gives intuitive analytical results, the space-vector approach reflects more dynamic insights of the system. This is achieved by using a unified dynamic modeling of both the ac system and the VSC by means of a new introduced modeling approach Jacobian transfer matrices. This approach shows that non-minimum-phase phenomena due to competing effects between alternating voltages and currents following phase-angle changes impose a fundamental limitation on the achievable bandwidth of the VSC-HVDC link. At moderate voltage levels, a VSC-HVDC link operating in alternating-voltage control mode is able to achieve higher bandwidth than in reactive-power control mode since the right-half plane (RHP) zero is located further from the origin in the former mode.

Harmonic and reactive current compensation using a voltage source inverter in a battery energy storage system

This paper presents a harmonic and reactive current compensator using a voltage source pulse-width modulated inverter. The proposed operation is included as part of the function of battery energy storage system in this study. The control strategy of inverter switching devices is based on the calculation algorithm from the instantaneous power theorem. Its main feature is to maintain the operation system with unit power factor, as well as to suppress the harmonic current generated from nonlinear loads. In this paper, different control methods are applied in simulations. Ramp control can be improved by a fine-tuned compensator, and its performance is proved both in simulation and experiment. In the battery energy storage system, the harmonic and reactive power control mode is also important to the overall operation. The proposed method promotes the battery energy storage system for wider applications.