Black Widow Optimization Algorithm-Based Sub Synchronous Resonance Investigation with Series Compensation

Series compensation of transmission line increases its power transfer capability, however leads to serious destructive phenomenon known as Sub-Synchronous Resonance (SSR). Several SSR mitigation techniques in wind power plant (WPP) are found in literature however, very little information is available on mitigation of SSR in a series compensated type 3 WPP using STATCOM. This paper reports the performance of remote power signal based STATCOM SSRDC for mitigation of SSR due to induction generator effect (IGE) in series compensated type 3 WPP. A first bench mark (FBM) model is adopted with type 3 WPP for SSR studies. A STATCOM with SSRDC is employed at PCC. It is shown that STATCOM with damping controller is capable of mitigating SSR even at higher rating of WPP and higher series compensation level. Electromagnetic transient simulations using MATLAB/Simulink have been carried out to analyze the performance of STATCOM with and without SSRDC for mitigation of SSR in series compensated type 3 WPP.

This paper investigates the sub-synchronous resonance (SSR) phenomenon in a series compensated doubly-fed induction generator (DFIG) based wind farms. A detailed linear state space model of a fixed-series compensated DFIG wind farm is presented for different operating point conditions. The model of the system includes a wind turbine aerodynamics, a 6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order induction generator, a 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order two-mass shaft system, a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order series compensated transmission line, an 8 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order rotor and generator side converter controllers, and 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> order DC link model. The 22 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order system is modeled in Matlab/Simulink, and modal analysis is performed on the modeled DFIG wind farm, and eigenvalues of the system are calculated. The eigenvalue analysis and time-domain simulation results show that SSR can potentially occur in the fixed-series compensated DFIG-based wind farm even at realistic levels of series compensation. The fixed-series capacitor is replaced with a gate-controlled series capacitor (GCSC), which is a series flexible ac transmission system (FACTS) device composed of a pair of gate-commutated switches in parallel with a capacitor that enables one to control impedance and power flow of transmission lines, for series compensation and SSR damping. The root-locus analysis is employed to design a SSR damping controller (SSRDC) for the GCSC. It is shown than a well-designed SSRDC for the GCSC can alleviate the SSR in DFIG-based wind farms. The IEEE first benchmark model adapted with a DFIG-based wind farm is employed as a case study.

The subsynchronous resonance (SSR) is an important problem in the power system, and especially the series compensated transmission lines may cause SSR in the turbine generators, such that it leads to the electrical instability at subsynchronous frequencies and potential turbine-generator shaft failures. Taking the Vietnamese Vungang thermal plants as an example, a shaft failure of Vungang I thermal power unit has occurred on November 24, 2015, due to SSR. The main cause for this failure is a resonance caused by the series capacitors on the 500 kV grid. This paper analyzes the SSR based on the location of shaft cracks and turbine generator mode shape for Vungang I and II thermal power plants. On the basis of that, it develops a novel control strategy for each Flexible AC Transmission system (FACTS) device as the thyristor controlled series compensator (TCSC), static VAR compensator (SVC), and static synchronous compensator (STATCOM). Then they are comparable to one another in order to choose a feasible solution for mitigating the SSR. The effectiveness of the proposed control strategy is verified via time domain simulation of the Vietnamese 500/220 kV transmission system using EMTP-RV and PSS/E programs. The obtained results show that the proposed strategy for SVC can be applied to immediately solve the difficulties encountering in the Vietnamese power system.

In the European UCTE system the share of renewable energy particularly of wind energy will grow essentially in the near future. Renewable energy is supported by the European union and the national governments. In Germany it is planned to extend the wind power generation from about 14000 MW at present to more than 40000 MW in 2030, In the present wind power generation was located in the medium voltage distribution systems with small wind parks size below 100 MW. The locations and the available wind onshore for larger units are limited. The new tendency is to install large wind parks off-shore with hundreds of MW power size in the North Sea and Baltic Sea. Depending on the size and distance to the on-shore transmission grid high voltage sea cable connections with distances up to 200 km have to be planned and installed. The transmission system operator (TNO) defines a wind park to operate in the same way as a conventional power plant. New rules have been collected in the grid code to define the interconnection with the grid and the control behaviour of the wind generators. Depending on the increase of wind energy an overcapacity of existing plants has to be retired. As a consequence of the wind nature wind generators are related to lower reliability and low average output in undesired time periods. Offering the necessary system reserve will become more and more an expensive and complex task. A second severe aspect are the uncontrolled load flows in and out of the control areas of the TNO's depending on the changing wind conditions. In some cases the (n-l)-principle of the transportation system can not be fulfilled as a consequence of additional wind energy flows through the system. These congestions have a high impact on the security and safety margins of the system and reduce free trading of power in the system. A very precise wind forecast is of essential importance in addition to a suitable reliability of the wind parks itself. The transmission system operator demand active and-reactive power support of wind generators to the grid during and after faults.

The random and intermittent nature of wind power (WP) makes the integration of large-scale wind farms into power system problematic. The energy storage system (ESS) is an effective means to smooth the WP. This paper presents a novel Kalman filter (KF) based adaptive wind power smoothing method to determine the power output of an ESS. ESS capacity can be significantly reduced by adjusting the parameters of KF adaptively according to the WP fluctuation. Meanwhile, a fuzzy logic controller is introduced to manage the remained energy level (REL) of the ESS. By considering the current WP fluctuation, the REL and the power output of the ESS together in the controller, the REL can be successfully managed to a reasonable range without deteriorating the WP fluctuation. A test case based on data from an actual wind farm validated the effectiveness of the proposed method.

For stable integration of large-scale wind farms, integration standards (Grid codes) have been proposed by the system operator. In particular, voltage control of large-scale wind farms is gradually becoming important because of the increasing size of individual wind farms. Among the various voltage control methods, Secondary Voltage Control (SVC) is a method that can control the reactive power reserve of a control area uniformly. This paper proposes hybrid SVC when a large-scale wind farm is integrated into the power grid. Using SVC, the burden of a wind turbine converter for generating reactive power can be reduced. To prove the effectiveness of the proposed strategy, a simulation study is carried out for the Jeju system. The proposed strategy can improve the voltage conditions and reactive power reserve with this hybrid SVC.

Nowadays, integration of large-scale wind farms (WFs) into power systems is experiencing rapid growth. As this rapid integration can affect transient stability significantly, employing doubly fed induction generator (DFIG)-based wind turbines, which have shown better behavior regarding system stability, has attracted much attention. This research contributes to the literature by investigating the transient stability of the power system with increasing penetration of DFIG-based WFs. In the proposed framework, the current-balance form is utilized for the network equations, and in this way, transient stability is performed using time-domain simulation. According to the simulation results, when the rate of wind power generation exceeds 0.7 per-unit, the increasing trend of the critical clearing time (CCT) is reversed and the CCT decreases greatly with the increased wind power penetration. In addition, the reactive power compensation by DFIG, the gearbox ratio, the power system strength, and DFIG parameters are comprehensively investigated as effective parameters on transient stability. Since the rated rotor speed of DFIG significantly impacts the electrical torque and machine currents, the reduction of the rated rotor speed due to the change of the gearbox ratio has been investigated as one of the effective factors to improve the transient stability. The simulation results demonstrate the effectiveness of the proposed approach in improving power system transient stability.

Repowering a wind farm enhances its ability to generate electricity, allowing it to better utilize areas with high mean wind speeds. Pakistan’s present energy dilemma is a serious impediment to its economic development. The usage of a diesel generator as a dependable backup power source raises the cost of energy per kWh and increases environmental emissions. To minimize environmental emissions, grid-connected wind farms enhance the percentage of wind energy in the electricity system. These wind generators’ effects, on the other hand, are augmented by the absorption of greater quantities of reactive electricity from the grid. According to respective grid codes, integration of commercial onshore Large-Scale Wind Farms (LSWF) into a national grid is fraught with technical problems and inter-farm wake effects, which primarily ensure power quality while degrading overall system operation and limiting the optimal use of attainable wind resources. The goal of this study is to examine and estimate the techno-economic influence of large-scale wind farms linked to poor transmission systems in Pakistan, contemplating the inter-farm wake effect and reactive power diminution and compensating using a range of voltage-ampere reactive (VAR) devices. This study presents a partial repowering technique to address active power deficits produced by the wake effect by raising hub height by 20 m, which contributed to recovering the active power deficit to 48% and so reduced the effects of upstream wind farms. Simulations were conducted for several scenarios on an actual test system modeled in MATLAB for comparative study using capacitor banks and different flexible alternating current transmission system (FACTS) devices. Using the SAM (System Advisor Model) and RETscreen, a complete technical, economic, and environmental study was done based on energy fed into the grid, payback time, net present value (NPV), and greenhouse gases (GHG) emission reduction. The studies suggest that the unified power flow controller (UPFC) is the optimum compensating device via comparison analysis as it improved the power handling capabilities of the power system. Our best-case scenario includes UPFC with hub height augmentation, demonstrating that it is technically, fiscally, and environmentally viable. Over the course of its lifespan, the planned system has the potential to save 1,011,957 tCO2, resulting in a greener environment. When the energy generated annually by a current wake-affected system is compared to our best-recommended scenario, a recovered shortfall of 4.851% is seen, with improved system stability. This modest investment in repowering boosts energy production due to wake effects, resulting in increased NPV, revenue, and fewer CO2 footprints.

This paper investigates the subsynchronous interactions (SSI) in DFIG-based wind farm and turbine-generator (T-G) bundled system which is integrated through series compensated transmission line, the results reveal that the integration of DFIG-based wind farm could improve the subsynchronous resonance (SSR) damping of the nearby turbine-generators. Then supplemental controls of DFIG-based wind farm are used to mitigate subsynchronous control interaction (SSCI) of the DFIG and multi-mode SSR of the nearby turbine-generators. The supplemental controls are added to the reactive power control loop of GSC (grid side converter) for DFIG. Given that no additional device is needed, this supplemental control could be the most promising measure for SSR and SSCI mitigating.

This paper investigates a special class of dynamic power system problem, namely subsynchronous resonance (SSR) resulted from a series-compensated network connecting doubly-fed induction generator (DFIG) based wind farms. A novel two-degree-of-freedom (2DOF) control strategy combined with a damping control loop is designed and analyzed for enhancing the system stability and alleviates the SSR that may arise due to the induction generator effect (IGE). The proposed control strategy is tested at different operating conditions of series compensation levels and low wind speeds to ensure the system stability. The doubly-fed induction generator based wind farms without the proposed control strategy leads to overall system instability during high series compensation and low wind speeds. Hence, the mitigation of the SSR and damping enhancement are critical to the entire power system stability. A reliable way of analyzing the system and designing effective control strategies against SSR based on the eigenvalue analysis and impedance based stability criterion is deployed. Moreover, analytical explanations have been elaborated to verify the procedure of the controller design. Fault ride-though capability has also been investigated with the proposed control strategy that is flexible to be integrated with the FRT schemes so as to assist the wind farm in mitigating the SSR during the fault recovery stage. Finally, time domain simulations are carried out to demonstrate the effectiveness of the proposed control strategy for mitigating the SSR and damping power system oscillations.

With the integration of large-scale wind farm of direct-driven permanent magnet synchronous generator (PMSG) type into power systems, the impacts on the existing power system have to be evaluated elaborately and systematically. This paper will discuss the impact of grid-connected wind farm of PMSG type on power system small signal stability. First, a simplified practical model of wind farm of PMSG type is derived for analyzing small signal stability in this paper. The rotor-flux-oriented control strategy is applied in the modelling of PMSG. Second, the simulation scenario involving replacing synchronous generator with wind farm of PMSG type based on the IEEE 3-generator-9-bus test system as benchmark is carried out to conduct the eigenvalue analysis and to assess the effect of wind farm of PMSG type on power system small signal stability. Finally, some preliminary conclusions and comments are drawn according to the simulation results.

With large scale wind farm integration, the effect of wind farm dynamic equivalent model accuracy is increasing on power system dynamic and transient stability, so the traditional equivalent and multi-group method can't meet requirement of some studies. Therefore, due to the deficiency of traditional wind farm equivalent method, a new multi-group method is proposed in this paper. Wind farms dispersity and wind turbines difference have been both considered in this method. When grouping wind farm turbines, based on that, a modified wind farm dynamic equivalent model is proposed using coherency method.For the contrastive analysis, three traditional equivalent models are built too, and simulated research of single, two and three phases short circuit is proceeded. Using relative error index of active power, reactive power and bus voltage, dynamic characteristics contrastive analysis of four equivalent models including the proposed model is preceded too. The superiority of this proposed method is verified by simulation results, and dynamic characteristics of the proposed model located on the parallel point are more close to that of real wind farm.

Economic feasibility of a wind-battery system in the electricity market with the fluctuation penalty

Flexible AC Transmission System devices are reactive power compensation devices employed to suppress the sub synchronous resonance (SSR) in the systems. The main important issue in the transmission lines of power system is SSR and it occurs during the condition, when series compensator is employed to improve the reactive power. It occurs at sub synchronous frequencies due to Electrical instability occurs as the result of shaft failures. Different FACTS devices such as the Static Synchronous Reactor (SSR), Static Synchronous Series Compensator (SSSC), Static Synchronous Compensator, Thyristor Controlled Series Compensator (TCSC), and Unified Power Flow Controller (UPFC) are analysed and reviewed in terms of SSR mitigation to develop a new strategy to mitigate SSR in the system. The new Multilevel inverter-based control strategy will be designed and developed based on the review and analysis using MATLAB Simulink to mitigate the SSR.

The contribution of wind power in conventional generation is increasing rapidly now-a-days. Hence a better understanding of wind power plants is required. But the wind power plants generally containing induction generators exhibit a rather different behavior than the conventional power plants which use synchronous generators. The purpose of this paper is to analyze and study transient stability of a wind farm based on conventional fixed speed Induction generator when it has been integrated with a weak grid. A comparative analysis of the transient stability improvement of a FSIG wind plant has been done, when it is supported with FACTS like S.V.C and STATCOM of equal ratings. Single case of transient condition i.e. a three phase fault has been studied by simulation. With the increase in demand of power and decrease of fossil fuels, mankind has been forced to search alternative sources for the generation of electricity. Wind power in spite of being stochastic in nature has proved itself as a viable solution to this problem. As the wind turbine technology is developing at a good pace, more and more wind power plants are being integrated with the conventional form of generation. With the increase in the ratio of wind generation to conventional generation, several problems related with integration of wind farms have emerged. These problems are due to distinct properties of the generators used with the conventional form (Thermal & Hydro) of generation and wind based generation (1)-(4). In thermal and hydro power based generation synchronous generators are used while in wind based generation mostly induction generators are used. Induction and synchronous generators do not exhibit similar behavior during power system stresses (transients). Moreover, increase in wind power based generation requires a reliable transmission system for power evacuation to the load centers. As the wind farms are mainly concentrated in far flung and rural areas their interconnection with the grid becomes a problem. This problem is mainly due to the existence weak transmission grids in the rural areas (1)-(4). Earlier when the share of wind power generation as compared with the conventional generation was low, during transient conditions; whenever the power system reached on the verge of instability the wind farm was disconnected from the grid and was reconnected when transients passed away. But as the share of wind power in the conventional generation increased, the practice of disconnecting the wind farms from the rest of the grid led to the drop in frequency of the power system. So now-a- days even if a fault occurs in the power system somewhere near the wind farms, they still remain connected with the grid for a critical time period. This phenomenon is called fault ride through (FRT) in wind farms (5). This paper has studied a transient condition (fault) in a grid connected fixed speed induction generator based wind farm and its fault ride through performance. A comparison of the performance of fact devices like static var compensators (svc) and static synchronous compensators (statcom) in improving the transient stability of wind farms during fault is also done.