This study presents a strategy involving a reduction in the stator current sensor count for control of power converters, in a doubly fed induction generator (DFIG)‐based wind energy conversion system ...(WECS). The reduced sensor vector control scheme is effectively used in lieu of the conventional vector control algorithm during sensor failure without any change in the overall control structure. This keeps the system operational in case of sensor failure. The reduced sensor scheme necessitates precise estimation of stator flux amplitude and an orientation angle, for control of power converters under all operating conditions. A composite generalised integrator phase‐locked loop is presented to estimate accurately the stator flux amplitude and orientation angle, even at operating system irregularities such as unbalanced voltages, lower‐order harmonics in the grid voltage, DC bias in sensing circuitry, and so forth, which otherwise lead to distortions in flux and orientation angle. The grid‐side converter control is based on a twin frequency improved second‐order generalised integrator. It enables fast and accurate power quality improvement in DFIG‐based WECS during load and grid abnormalities. A laboratory prototype is developed to validate the control of the system.
This article deals with a phase-locked loop (PLL)-based novel control for wind turbine driven doubly fed induction generator interfaced to utility grid with a battery energy storage (BES) connected ...at the dc link. The control of grid-side converter (GSC) is modified to export/import constant power to/from the grid. The state of charge of BES helps in deciding the reference export power to the grid apart from the manual selection using averaged wind power in a particular period of time. An off maximum power point tracking logic is incorporated in the rotor-side converter (RSC) control to operate the BES within its constraints and, moreover, to feed constant power to the grid. In addition, the energy management scheme of the system is presented in the form of flowchart for both exporting and importing power to/from the grid. The RSC and GSC have taken care of unity power factor operation at stator terminals and to mitigate harmonics and grid currents balancing, respectively. The system performance is found robust as the PLL response is not affected even under grid voltages with dc offset. The system is modeled and simulations are carried out in MATLAB using SimPowerSystems tool box. Moreover, the control scheme performance is compared with conventional control algorithms both in terms of PLL and converter controls. To validate the effectiveness of the control scheme, a prototype of the system is developed. Test results demonstrate the satisfactory performance of the system under various operating conditions.
This paper proposes a novel single input variable fuzzy logic controller (FLC) strategy for a wind turbine driven doubly fed induction generator (DFIG) with a battery energy storage in autonomous ...mode. The proposed control scheme has multi-functionalities such as harmonic elimination, compensation of unbalanced load currents, and extraction of maximum power from the wind. The control of rotor side converter and load side converter is based on the field-oriented approach. The proposed single input variable FLC-based control has good dynamic response as compared to conventional control algorithms. The tip speed ratio-based maximum power point tracking technique is used to extract maximum power from the wind. The simulation of DFIG-based wind power generation system is carried out under various conditions, such as constant wind speed, variable wind speeds, and load currents unbalancing, using Simpower Systems toolbox of MATLAB. The DFIG stator voltages and currents are found balanced and sinusoidal by maintaining constant frequency and voltage at PCC. Finally, a prototype of DFIG-based wind energy system is developed in the laboratory to verify the performance of the proposed control scheme at variable wind speeds and linear, nonlinear loads. The total harmonic distortions of the DFIG stator voltages and currents are obtained within the limits of the IEEE 519 standard.
This paper presents the grid interactive wind-solar-diesel generator (DG) based microgrid (MG) at unpredictable weather conditions with improved reliability of power. With enhanced reliability, loads ...are powered continuously during both on-grid and off-grid modes. In view of sensitive loads, DG is used in the system on grounds of its dispatchability, which is lacking in the wind-solar power generation. However, DG is controlled to consume minimum fuel during its operation. The wind power is captured by using a doubly fed induction generator (DFIG). Moreover, a battery bank is connected in the system for energy storage and to deliver when its need arises. Modified controls are presented for converter on rotor side (CRS) and converter on load side of DFIG to make MG flexible for on/off-grid operations and for smooth connection/disconnection of DG. An adaptive step change incremental conductance based maximum power point tracking (MPPT) technique is utilized for acquiring peak power from solar photovoltaic (PV) array. Moreover, a modified adaptive step change based perturb and observe wind MPPT strategy is incorporated in control of CRS for improved power capturing as compared to conventional fixed step methods. Simulated results are presented to evidence MG performance along with a comparison of wind turbine efficiency. Moreover, an experimental test bench is built to evidence dynamic and steady state performance of MG at various operating scenarios i.e., at varying winds and varying solar irradiances, during on/off-grid modes and smooth connection/disconnection of DG, and at change in loads.
This paper presents a synchronizing control for wind turbine (WT) driven doubly fed induction generator (DFIG) system with DG (Diesel Generator) in a remote area consisting of solar photovoltaic (PV) ...array and the battery energy storage. The DFIG is operated with two voltage source converters (VSCs) namely VSC on rotor side (VSCR) and VSC on load side (VSCL) by sharing common DC link with a battery. Moreover, the solar PV array is connected to the DC link through a boost converter, which is used to acquire peak power from the PV array. The microgrid is designed with minimum power converters with enhanced reliability and reduced intermittency especially for islands. Moreover, two controls are presented for successful and smooth operation of microgrid. An additional frequency loop is added in the control of VSCR for minimizing the power fluctuations and for smooth connection of DG to DFIG-solar-battery based isolated microgrid with static transfer switch. Moreover, the VSCR control is framed to build the rated voltage at the DFIG stator with control over ON/OFF operation of VSCR. It is also designed to harness the maximum power from wind. The control of VSCL is framed to regulate the DG power to operate it in optimal fuel consumption zone whenever it is synchronized. Simulations are performed at steady and varying wind speeds, varying PV insolation and at unbalanced connected loads. Moreover, a prototype of isolated microgrid is developed in the laboratory and its experimental performance is investigated at different operating scenarios to evidence its robustness.
This article presents a green energy solution to a microgrid for a location dependent on a diesel generator (DG) to meet its electricity requirement. This microgrid is powered by two renewable energy ...sources, namely wind energy using doubly fed induction generator (DFIG) and solar photovoltaic (PV) array. The solar PV array is directly connected to common dc bus of back-to-back voltage source converters (VSCs), which are connected in the rotor side of DFIG. Moreover, a battery energy storage is connected at the same dc bus through a bidirectional buck/boost dc-dc converter to provide a path for excess stator power of DFIG. The extraction of maximum power from both wind and solar is achieved through rotor side VSC control and bidirectional buck/boost dc-dc converter control, respectively. A modified perturb and observe algorithm is presented to extract maximum power from a solar PV array. Moreover, the control of load side VSC is designed to optimize the fuel consumption of DG. A novel generalized concept is used to compute the reference DG power output for optimal fuel consumption. The microgrid is modeled and simulated using SimPowerSystems toolbox of MATLAB for various scenarios such as varying wind speeds, varying insolation, effect of load variation on a bidirectional converter, and unbalanced nonlinear load connected at point of common coupling. The DFIG stator currents and DG currents are found balanced and sinusoidal. Finally, a prototype is developed in the laboratory to validate the design and control of it.
Unbalanced grid voltages, appearing at stator terminals of a doubly fed induction generator based wind energy conversion system, deteriorate its performance by instigating unwanted oscillations and ...distortions in output grid power and rotor currents, respectively, as well as by introducing unbalanced currents in the stator and the grid. This article aims to address these challenges using a coordinated control strategy based on an improved reduced order generalized integrator (IROGI) for positive and negative sequence estimation (PNSE). The IROGI-PNSE further enhances the control performance by eliminating the effects of dc component or unbalance in sensed voltages, on the grid synchronization. The coordinated control strategy uses hysteresis scheme for current control. The hysteresis-based current control requires fewer rotational transformations, and eliminates the need for PI/PIR regulators and notch filters for inner current control loops. This renders the control, computationally efficient. Moreover, the presented system is equipped to exhibit wind power leveling functionality through a battery energy storage. An approach, employing the region-specific wind speed frequency distribution graph, is utilized to constitute the power leveling operation modes. The effectiveness of the control scheme is demonstrated through test results on a prototype developed in the laboratory.
This article presents a photovoltaic (PV)-battery and wind driven doubly fed induction generator (DFIG) based grid-connected system with an improved multifunctional control scheme for grid-side ...converter (GSC). A three-stage improved reduced-order multiple integrator control is used to maintain the reactive power into the grid as well as it regulates the dc-link voltage across the GSC. The grid side control improves power quality in different abnormal conditions. Moreover, it behaves in such a way that it reduces the rise time, the maximum peak overshoot, as well as the settling time during the transients. The rotor side converter is used to provide the required amount of reactive power using the field-oriented control, for the wind power generator (WPG). A DFIG is used as a WPG. The single-stage PV array and a battery with bidirectional converter are connected to the common dc link of the GSC. The battery helps to extract the maximum wind power in light load conditions. The charging and discharging of the battery depend on the renewable energy generation and load demand. The dynamic behavior is improved by adding a PV feedforward term with the total active load current component. Here, the stator current total harmonic distortion (THD) and grid current THD are maintained as per the IEEE standard. Simulated and test results show the performance of the developed system in different dynamic conditions, such as load unbalancing, changes in PV insolation, and change in speed from the cut-in to cut-out speeds of the wind turbine. Moreover, these results show the battery behavior during different dynamic conditions.
This article presents the sharing of reactive power between two converters of a doubly fed induction generator (DFIG) based wind energy conversion system interacting with the grid. The rotor side ...converter (RSC) control of DFIG is designed for sharing of reactive power at below rated wind speeds, which essentially reduces the amount of rotor winding copper loss. However, at rated wind speed, the RSC control is designed to maintain the unity power factor at stator terminals and to extract rated power without exceeding its rating. Further, the reduction in rotor winding copper loss due to reactive power distribution is demonstrated with an example. Moreover, the grid side converter (GSC) control is designed to feed regulated power flow to the grid along with reactive power support to DFIG and to the load connected at point of common coupling. Moreover, the GSC control is designed to compensate load unbalance and load harmonics. The battery energy storage connected at dc link of back-to-back converters, is used for maintaining the regulated grid power flow regardless of wind speed variation. The system is modeled and its performance is simulated under change in grid reference active power, varying wind speed, sharing of reactive power, and unbalanced nonlinear load using SimPowerSystems toolbox of MATLAB. Finally, a prototype is developed to verify the system steady state and dynamic performance. Moreover, system voltages and currents are found sinusoidal and balanced, and their total harmonic distortions are as per the IEEE 519 standard.
Wind energy conversion systems (WECSs) based on doubly fed induction generator (DFIG) are often connected to local loads, and excess power is supplied to the grid. The nonlinear and unbalanced local ...loads integrated with WECS, degrade the power quality by injecting harmonics and negative sequence components in grid currents. Another major concern in grid-integrated WECS is related to sudden steep fluctuations in wind and load powers, which bring about frequency and voltage deviations that ultimately affect grid stability. Thus, the objective of this work is twofold. First, to suppress harmonics and negative sequence components in grid currents, using a normalized least mean squares (NLMS) adaptive filtering scheme based on arctangent cost function (Arc-NLMS). The Arc-NLMS adaptive algorithm is robust against model uncertainties and exhibits optimal convergence performance. Second, to guarantee grid security amidst sudden erratic variations in wind speed or load power, through implementation of a power management scheme (PMS) using a battery energy storage. The PMS allocates exponential values to weight components, to diminish the effects of power fluctuations. Based on performance evaluation of the system using a developed laboratory prototype, the PMS proves to be effective in smoothening power fluctuations while the power quality issues related with connection of local nonlinear and unbalanced loads are also alleviated.
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