Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> Power systems with high penetration of wind power usually require long-distance transmission to export wind power to the market. Interarea oscillation is an issue faced in long-distance transmission. Can wind generation based on doubly fed induction generator (DFIG) help to damp oscillations and how? In this paper, a control scheme is developed for the DFIG with rotor-side converter to damp interarea oscillations. The DFIG is modeled in MATLABreg/Simulink utilizing its vector control scheme feature, and inner current control and outer active/reactive power control loops are modeled and designed. A two-area system that suffers from poor interarea oscillation damping along with a wind farm in the area that exports power is investigated. A damping controller is designed and time-domain simulations are used to demonstrate the effectiveness of the controller. The major contributions of the paper are as follows: 1) built a wind farm interarea oscillation study system based on the classical two-area four-machine system, 2) established that in vector control scheme, active power modulation can best help to damp oscillations, 3) successfully designed a feedback controller using remote signals with good interarea oscillation observability. <s> BIB001 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> As a consequence of technological progress, wind power has emerged as one of the most promising renewable energy sources. Currently, the penetration level of wind energy in power systems has led to the modification of several aspects of power system behaviour including stability. Due to this large penetration, transmission system operators have established some special grid codes for wind farms connection. These grid codes require wind farms to provide ancillary services to the grid such as frequency regulation and reactive power regulation. In the near future, the capability of damping system oscillations will be required. For this reason, the influence of grid-connected wind farms on system oscillations is reviewed in this paper, focusing on the contribution or damping of power system oscillations, and on inner wind turbine oscillations. <s> BIB002 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> This paper highlights the important considerations toward coordinated control of doubly fed induction generator (DFIG)-based wind farms for power oscillation damping. The effect of replacing one existing synchronous generator with a power system stabilizer (PSS) by a DFIG on the local mode and the mode shapes of the critical interarea modes are analyzed. With almost zero participation from the DFIG mechanical side and very little observability of low-frequency oscillatory modes in signals locally available at the wind farms, the choice of appropriate remote feedback signals is discussed. Relative controllabilities of the DFIG rotor current components are compared to determine the most effective control structure. A coordinated control design approach aimed at damping multiple oscillatory modes through more than one DFIG-based wind farm is demonstrated. Heuristic optimization is used for the design problem which is otherwise difficult to solve using an analytical approach. Modal analysis and nonlinear simulation results are presented to substantiate the findings. <s> BIB003 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> Several studies have recently reported the capability of doubly-fed induction generator (DFIG) wind farms in improving the dynamic performance of power systems. Since wind farms are more often located far from the system conventional generation centers, local signals do not comprise enough content for damping inter-area oscillations. This paper presents a particle swarm optimization (PSO)-based wide-area damping controller (WADC) for the DFIG wind farms. The proposed controller is designed with a centralized nature on the basis of latest technological development of wide-area measurement system (WAMS). Damping both inter-area and local oscillatory modes are intended in the design process. The most challenging deficiency against WAMS real-time applications is the variable communication latency which can deteriorate the system stability if not properly accounted for in the controller design process. The proposed WADC hence incorporates effective means to compensate for the destructive characteristics of WAMS delayed signals. The PSO technique is applied to normalize and optimize the parameters of WADC. A set of comprehensive case studies are conducted on a 16-bus six-machine test system and the obtained numerical evidences are thoroughly discussed. <s> BIB004 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> As the integration of a doubly fed induction generator (DFIG)-based wind power generation into power systems tends to increase significantly, the contribution of DFIG wind turbine is highly expected. Since the active and reactive power outputs of DFIG can be independently modulated, the stabilizing effect of DFIG on the inter-area power system oscillation is a challenging issue. This paper proposes a new robust control design of power oscillation damper (POD) for a DFIG-based wind turbine using a specified structure mixed H2/H∞ control. The POD structure is a practical 2nd-order lead–lag compensator with single input. Normally, H∞ control mainly enforces the closed-loop stability while noise attenuation or regulation against random disturbances is expressed in H2 control. As a result, the mixed H2/H∞ control gives a powerful multi-objective control design so that both closed-loop stability and performance of designed controller can be guaranteed. Here, the linear matrix inequality is applied to formulate the optimization problem of POD based on a mixed H2/H∞ control. The POD parameters are optimized so that the performance and robustness of the POD against system disturbances and uncertainties are maximal. The firefly algorithm is automatically applied to solve the optimization problem. Simulation study in a two-area four-machine interconnected power system shows that the DFIG with robust POD is superior to conventional POD in terms of stabilizing effect as well as robustness against various power generating and loading conditions, unpredictable network structure, and random wind patterns. <s> BIB005 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> This paper presents a damping control to mitigate sub-synchronous interactions (SSI) in doubly-fed induction generator (DFIG) wind turbines connected to series-compensated lines. This issue has gained attention due to the recent SSI phenomena reported in DFIG wind farms located near series capacitors. Two approaches which add a supplementary damping control signal are compared: one of them, integrated to the grid-side converter, and the other one, to the rotor-side converter. The SSI damping controls are designed using a multi-input multi-output state-space methodology. This allows to easily tune a high performance controller using several measurements and control inputs. Small- and large-signal stability analyses, robustness aspects, impact of the supplementary controls on the system modes, and influence of different operating conditions on the SSI are also discussed. The obtained results show that the supplementary control is able to properly damp the sub-synchronous oscillations of DFIG wind turbines by updating the existing DFIG control systems without the inclusion of expensive additional damping devices, and reducing the risk of wind generation tripping. <s> BIB006 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> This paper investigates the potential for wind power plants (WPPs) to damp interarea modes. Interarea modes may be the result of a single or a group of generators oscillating against another group of generators across a weak transmission link. If poorly damped, these power system oscillations can cause system instability and potentially lead to blackouts. Power conversion devices, particularly, megawatt-scale converters that connect wind turbines and photovoltaic power plants to the grid, could be used to damp these oscillations by injecting power into the system out of phase with the potentially unstable mode. In our model, this power may be provided by a WPP. Over time, the net energy injection is near zero; therefore, providing this static damping capability is not expected to affect the energy production of a WPP. This is a measurement-based investigation that employs simulated measurement data. It is not a traditional small-signal stability analysis based on Eigenvalues and knowledge of the power system network and its components. Kundurs well-known two-area, four-generator system and a doubly fed induction generator (DFIG)-based WPP are modeled in PSCAD/EMTDC. The WPP model is based on the Western Electricity Coordination Council (WECC) standard model. A controller to damp interarea oscillations is added to the WECC DFIG model, and its effects are studied. Analysis is performed on the data generated by the simulations. The sampling frequency is set to resemble the sampling frequency at which data are available from phasor measurement units in the real world. The YuleWalker algorithm is used to estimate the power spectral density of these signals. <s> BIB007 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> In this paper, the two-level hierarchical scheme, which consists of wide area centralized and local controls of the power oscillation damper (POD) installed with the doubly-fed induction generator (DFIG) wind turbine and the power system stabilizer (PSS) has been proposed for robust power oscillation damping. In the wide area level, the centralized POD and PSS has received the input signals from synchronized phasor measurement units (PMUs). The geometric measures of controllability and observability have been applied to select the suitable DFIG and synchronous generator (SG) for stabilizing the target oscillation modes, the proper input signals of the centralized POD and PSS, and the location of PMUs. In the local level, the suitable DFIG and SG have been equipped with POD and PSS, respectively. In the parameters optimization of POD and PSS, the practical issues such as damping performance, controller structure, communication latency, and robustness against system uncertainties have been considered. The controller efficiency and resiliency of the proposed controller have been evaluated in comparison with other controllers by eigenvalue analysis and nonlinear simulation for a wide range of operating conditions, line outage contingencies, severe faults, and communication failure. <s> BIB008 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> This paper proposes a second-order sliding mode-based damping controller of DFIG for interarea oscillations. The proposed damping control strategy aims to utilize the reactive power modulation ability of DFIG to stabilize the power system in the event of oscillations caused by disturbances. First, the proposed controller is derived based on a two-area power system, and then it is extended to multiarea power systems. Compared with the conventional damping controller, the proposed one is insensitive to modeling uncertainties and parameter variations. Given the wide variation of operation points, the proposed sliding mode-based damping controller demonstrates a better robustness than the conventional damping controller. Simulation results on a two-area power system and a 10-machine 39-bus power system with DFIG-based wind farm integration show the improvement on system performance in interarea oscillation damping and demonstrate the robustness of the proposed control scheme in a wide operation region. <s> BIB009 </s> Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review <s> E. POWER OSCILLATION DAMPING <s> This letter presents an active and reactive power coordinated damping controller for doubly fed induction generator (DFIG) using second-order sliding mode technique. Through simultaneously modulating active and reactive power of DFIG, the proposed controller has an enhanced damping performance. Its advantages include faster damping speed and robustness to modeling uncertainties and parameter variations. Simulation results have verified its superior performance over existing schemes. <s> BIB010
Power system oscillations can lead to instability and blackouts. WECS have the ability to damp inner wind turbine oscillations and power system oscillations BIB002 . Figure 16 shows the wind power plant oscillation damping concept. The wind power plant output power should be equal in magnitude but opposite direction compared with the system or network power. Traditionally, oscillations are eliminated by power systems stabilizers (PSS). Power oscillations are either power system oscillations or machine oscillations. Power system oscillations are further classified into inter-area and local modes while machine oscillations are classified into drive-train and control modes. Oscillations categories are outlined in Table 3 . In order to implement the suitable power damping control method, oscillation roots should be identified. Fixed speed wind turbines have positive impact on power system oscillation damping. However, variable speed wind turbines behavior depends on the control algorithm. Frequency control has the ability to improve power system stability while voltage control affects the power damping. All in all, the power oscillation can be eliminated by mechanical elements like pitch control or by electrical elements such as converter control BIB002 . Various research studies consider DFIG to reduce the effect of power oscillation. For example, a control method, which is implemented to the RSC of DFIG for iner-area oscillation damping, is presented in BIB001 . Moreover, the article BIB006 investigates oscillation damping using GSC and RSC and proposes a multi-input multi-output state-space methodology to mitigate sub-synchronous interactions (SSI) for DFIG systems connected to series compensated lines. It is found that the power oscillation damping using RSC has better performance compared to RSC. In BIB007 , a controller to damp inter-area oscillations is integrated to the DFIG classical control. Another BIB008 proposes a two-level hierarchical method for robust power oscillation damping. The method includes wide area centralized and local controls of the power oscillation damper (POD) installed with power system stabilizer (PSS) and DFIG based WECS. In addition, an inter-area power oscillation damping DFIG controller that is based on second-order sliding mode control is introduced in BIB009 . Reference BIB010 also proposes a prescribed convergence law algorithm, which is also a second order sliding mode strategy, for coordinated DFIG active and reactive powers oscillation damping control. Heuristic optimization control technique for coordinated power oscillation damping control of DFIG is proposed in BIB003 . The paper BIB004 considers an important aspect which is time varying signal latency when designing wide-area power oscillation damping controller. It is found that if signal latency occurs, the power oscillation damping controller will not be able to remove inter-area oscillations. As ideal communications can not be achieved in real world to solve this issue, latency issue is removed by an optimization strategy in the controller design stage. Finally, BIB005 proposes a specified structure mixed H 2 /H ∞ control based on linear matrix inequality LMI technique for power oscillation damping using DFIG.