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Single-phase matrix converters (MCs) are undergoing rapid developments due to their bipolar voltage gain (as required in dynamic voltage restorers) and step-changed frequency operation (used in high step-up ac–dc rectifiers, and to provide medium frequency isolation in traction and wind turbine converters, etc.). However, existing buck–boost MCs require high-voltage/current rating devices, and suffer from large component voltage/current stresses and ripples, significantly degrading their efficiency. This article proposes a highly efficient single-phase buck–boost MC; consisting of eight IGBTs (implemented using two full-bridge IGBT modules), second-order input and output filters, and a small value film capacitor. Efficient discrete inverting and noninverting buck and boost operations are proposed (same as that of sixteen-switch cascaded buck–boost MC) with significantly lower component voltage/current stresses and ripples. In addition, flexible inverting and noninverting buck–boost operations are proposed with independent control of buck and boost duty ratios. All of the proposed operations are free of commutation issues, compatible with reactive loads, and provide smooth input and output currents. Furthermore, all the switches have same voltage stresses, and all four switches in a full-bridge module experience the same current stresses. A comprehensive description of circuit operation is presented based on a number of proposed switch modulation strategies with a nonunity power factor load, followed by design guidelines, and comparative evaluations with existing topologies. Finally, experimental verification results are presented, using a 400-VA laboratory prototype converter. [ABSTRACT FROM AUTHOR]

This study presents a H∞ mixed‐sensitivity robust control design to improve the overall damping performance of low‐frequency oscillations for power systems with doubly fed induction generator‐based (DFIG) wind power generation. The supplementary damping controller is designed in the linear matrix inequality framework which allows the placement of the closed‐loop poles inside a pre‐defined region for improved stability. The damping signal is implemented at the reactive power modulation of the rotor‐side converter of the DFIG wind turbine (DFIG‐WT). The damping contribution of the power oscillator damper is compared with that provided by the power system stabiliser (PSS) of the synchronous generator (SG). State‐space system analysis and time‐domain simulations show the capability of DFIG‐WT to enhance the overall damping of the oscillatory modes even if PSSs are not installed at SG s. Also, the designed controller shows a robust performance to wind speed variations. The performance evaluation is based on the revised two‐area four machines system and the revised New England 39‐bus system. [ABSTRACT FROM AUTHOR]

Leading wind turbine manufacturers are running life extension programs for their installed wind farms which include fixed speed induction generator-based wind turbines (FSIG-WT). To accommodate the requirement of recent grid codes in these upgrades, this paper presents a new topological configuration to enhance the fault ride through (FRT) operation of FSIG-WT. The topology comprises ten semiconductor switches in total and performs shunt and series compensation concurrently in response to the dynamic grid conditions. A coordinated control strategy is developed for the proposed topology to ensure smooth steady state operation, enhanced transient response, and most importantly, FRT capability in adherence to the recent grid code requirements. In addition, the control strategy maintains the linear modulation range and uniform switching frequency across all the switches participating in series and shunt compensation. The validity of the proposed topology and the coordinated control strategy is verified through extensive simulation study under different operating conditions. [ABSTRACT FROM AUTHOR]

Being more actively involved in the electricity market and power systems, wind farms are urgently expected to have similar controllable behavior to conventional generations so that demand assigned by the system operator can be met. However, determining the method of dispatching the reference among the widely spread and low-rating wind turbines is difficult. This paper provides a cooperation-driven distributed control scheme for wind farm active power regulation. Instead of competing with neighboring controllers completely, the control strategy evaluates system-wide impacts of local control actions, and aims to achieve coordinated control effect. In addition, the kinetic energy storage potential in a wind turbine is tapped to provide a buffer for power dispatch. Case studies demonstrate that a large wind farm can be effectively controlled to accurately track the demand power through the proposed control scheme. [ABSTRACT FROM PUBLISHER]

This study presents a new scheme for a continuously variable (CV) series braking resistor (SBR) with independent per phase controller. The CV-SBR is a CV and not stepwise. A novelty of the work presented is that the CV-SBR operates on the whole range of wind speeds. The proposed scheme is applicable to fault ride-through (FRT) of fixed speed wind turbines (FSWTs). The CV-SBR scheme is compared to the single-step (SS) and multi-steps (MS) SBRs. The CV-SBR scheme is modelled and simulated in PSCAD/EMTDC™. The performance of the wind turbine is studied for balanced and unbalanced fault scenarios. The CV-SBR scheme is advantageous over the other two candidates with its ability to limit the fault current and reduce the turbine speed deviation at any wind speed. The CVSBR is employed with a static synchronous compensator (STATCOM) to allow FRT of FSWT connected to weak grid during nearby faults and to deliver the reactive current required by some grid codes. The CV-SBR scheme is successful in reducing voltage disturbance's consequences on the generator's mechanical system. Simulation results show that the CV-SBR allows FRT of FSWT connected to weak grid where the STATCOM alone is not able to sufficiently enhance the FRT of FSWT during nearby faults. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulated series dynamic braking resistor (MSDBR) control strategy for enhancing the fault ride-through (FRT) of doubly fed induction generator-based wind turbines. The proposed cost-effective protection scheme introduces a voltage booster that offers series voltage compensation capability and provides a means of power evacuation to mitigate the power imbalance during grid faults. To attain flexible and robust control solution for handling both balanced and unbalanced grid faults, the proposed scheme employs a modulated pulse width modulation (PWM) switching technique to control the stator phase voltage individually. The proposed transient management scheme allows the MSDBR to mitigate the impact from different types of grid faults and to fulfill with the recent grid code requirement. Also, reactive current injection capability during faults is also investigated with the proposed voltage reference algorithm. For the controller design, small-signal modeling is utilized with consideration of measurement dynamics for the tuning of controller parameters in order to ensure the system robustness and stability. Finally, the simulation results demonstrate the satisfactory performance of the MSDBR with its preferred allocation for enhancing the FRT performance against both balanced and unbalanced faults. [ABSTRACT FROM AUTHOR]

This paper presents a novel dc-link scheme for enhancing the fault ride-through (FRT) capability of doubly fed induction generator-based wind turbine (DFIG-WT). The proposed system consists of parallel capacitors with a dedicated control strategy designed to provide means for power evacuation during grid fault conditions. This technically simple and cost-effective scheme was developed considering transmission line autoreclosing which may cause multiple fault inceptions. Simulation studies were carried out to compare the performance of the introduced solution with a DFIG-WT, equipped with the dc chopper and crowbar. The simulation results demonstrate the enhanced performance of the proposed approach in maintaining the dc-link voltage, transient rotor voltages, and currents within the permissible operating range during a bolted three-phase-to-ground fault. The proposed schemes were also tested in response to asymmetrical grid faults, and the enhancement in transient response has been verified. An experimental setup was developed to emulate the behavior of the dc-link circuit during fault conditions. These experimental results demonstrate the effectiveness of the switching parallel capacitors in preventing dc-link overvoltage during imbalance power operation. The discharging capacitor circuit highlighted the capability of tackling the multiple fault inception problems while adhering to grid code requirements. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel coordinated voltage-control (CVC) scheme for distributed generations (DGs) that relies on adaptively changing the roles (master or slave) of the devices [inverter-based DG, diesel generator, and online tap changer (OLTC)] within the smart grid, depending on system conditions. In addition, the proposed scheme imposes different control response and bandwidth on the devices to coordinate the reactive power among distributed generations (DGs) and OLTC steps. The main objective of the proposed method is twofold: 1) to maximize the reactive power reserve of DGs and, hence, facilitate reaction during contingency situations and 2) to provide voltage regulation during normal operating conditions. The simulated distribution system includes inverter-based DGs (photovoltaic and wind turbine), diesel generator, and OLTC and the potential of the CVC scheme is evaluated and analyzed in view of improving voltage profile, maximizing the reactive power reserve, enhancing fault ride through and improving the transient stability margin. The control algorithm is examined under steady state, load excursion, and three-phase-to-ground fault conditions. The results demonstrate the ability of the proposed CVC scheme to satisfy the targeted objectives with significant improvement in the maximum critical clearing time. The proposed scheme is independent of real-time measurements and is widely adaptive to the dynamics of power systems, thus making it quite suitable for utility implementation. [ABSTRACT FROM AUTHOR]

This paper presents new series grid interface topologies for enhancing the low voltage ridethrough capability of self-excited induction generator-based wind turbines. Two proposed schemes: static synchronous series compensator (SSSC) and controllable series braking resistor (CSBR) have been designed and simulated. The test system simulated represents a wind turbine connected to an electric grid with alternatively employing SSSC and CSBR. The potential of the two schemes is evaluated and analyzed using positive and negative-sequence reference frames in response to balanced and unbalanced fault scenarios. The simulation results using PSCAD/EMTDC demonstrate the performance of the proposed schemes for improving the fault ridethrough capability and transient stability margin in response to severe symmetrical and asymmetrical grid faults. The schemes have shown successful and fast mitigation of voltage disturbance consequences on the mechanical system. The schemes helped the wind turbine to remain connected with considerable isolation from grid faults. [ABSTRACT FROM PUBLISHER]

The paper proposes a novel fault ride-through (FRT) configuration with a transient management scheme to provide dynamic grid supports for self-excited induction generator (SEIG)-based wind turbines. The new configuration is capable of supporting both shunt and series compensation modes for enhancing FRT capability and transient stability. The proposed control scheme, utilizing positive and negative sequence controllers, provides a transient management solution for both balanced and unbalanced fault conditions. An active damping control loop for the shunt compensation configuration is developed to mitigate system oscillation and improve system performance during and following faults. A comprehensive simulation has verified the FRT capability of the new configuration and transient management scheme, and showed that the proposed topology increases system stability under various short circuit ratios, even in case of a weak grid. The experimental results are also carried out to show the effectiveness of the proposed shunt-series reconfiguration topology. [ABSTRACT FROM PUBLISHER]

This paper presents series grid interface topologies for enhancing the fault ride-through (FRT) performance of doubly-fed induction generator (DFIG)-based wind turbines (WTs). Two voltage booster schemes, 1) dynamic voltage restorer (DVR) and 2) resistive type high temperature superconducting fault current limiter (HTS-FCL), are designed and implemented. The test system represents a WT connected to an electric grid with alternatively employing DVR and HTS-FCL. Both schemes provide fast mitigation of voltage dip that maintains the nominal operating conditions for DFIG-WT. To achieve a flexible control solution for balanced and unbalanced fault conditions, the DVR employs positive and negative sequence controllers while the HTS-FCL is designed to perform fast quenching for each phase individually. The potential of the two booster schemes is evaluated and analyzed in positive and negative sequence reference frames. Comprehensive simulation studies are presented to verify the capability of the series grid interface schemes for ensuring the normal operation and smooth wind power evacuation with effective isolation from grid faults. Furthermore, the grid code requirements of reactive current support are evaluated for both schemes at various fault scenarios. [ABSTRACT FROM PUBLISHER]

Integration of dynamic grid support is required for distributed power systems that are interconnected with medium voltage grids. This study proposes a comprehensive control solution to enhance fault ride through (FRT) capability for utility‐scale photovoltaic (PV) power plants. Based on positive and negative sequence control schemes and PV characteristics, the approach alleviates dc‐bus double‐line‐frequency ripples, reduces voltage stress on inverter power switches and DC‐link capacitors, and minimises undesirable low‐order voltage and current harmonics that are presented on the ac side. The study proposes a new feature to achieve superior FRT performance by using the overload capability of grid‐tied inverters. A weak electric grid is used for the test case including a wind turbine induction generator, diesel engine driven synchronous generators and various loads. A comprehensive simulation verified the capability of the proposed control schemes for mitigating the voltage dip, enhancing the voltage response and further improving the stability of interconnected distributed generation in reaction to severe unbalanced voltage conditions because of asymmetrical grid faults. [ABSTRACT FROM AUTHOR]