Abstract:The transient synchronization characteristics and instability mechanism of the permanent magnet synchronous generator (PMSG)-based grid-forming wind energy conversion system (GFM-WECS) under symmetrical grid fault have received little attention to date. In this paper, considering the dynamics of DC-link voltage, the transient stability and an improved control strategy of PMSG-based GFM-WECS are studied in detail. Firstly, considering the dynamic interactions between the machine-side converter and the grid-side converter, the large-signal equivalent model of GFM-WECS is established. Furthermore, a novel Lyapunov function is derived to evaluate the transient stability margin and instability boundary of GFM-WECS during grid voltage sag. Additionally, the impacts of current-limitation control on the transient stability of GFM-WECS are revealed. Then, a stability evaluation index is proposed to evaluate the transient stability margin of GFM-WECS. Moreover, an improved control strategy is proposed to enhance the transient response characteristics and low voltage ride-through (LVRT) capability of GFM-WECS under symmetrical grid fault. Finally, simulations and experimental results are conducted to verify the effectiveness of the proposed control strategy.

Abstract:Due to interconnection of various renewableenergies and adaptive technologies, voltage quality andfrequency stability of modern power systems are becomingerratic. Superconducting magnetic energy storage (SMES),for its dynamic characteristic, is very efficient for rapidexchange of electrical power with grid during small andlarge disturbances to address those instabilities. In addition,SMES plays an important role in integrating renewablesources such as wind generators to power grid by controllingoutput power of wind plant and improving thestability of power system. Efficient application of SMES invarious power system operations depends on the properlocation in the power system, exact energy and powerratings and appropriate controllers. In this paper, an effortis given to explain SMES device and its controllability tomitigate the stability of power grid integrated with windpower generation systems.

Abstract:Pakistan is an energy-resourceful country with vast and untapped renewable energy sources (RESs). The wind, solar, and biomass of the country are practically capable of ending a power sector collapse caused by demand-supply variances. A significant percentage of Pakistan’s population resides in rural areas. For rural population, the lack of connection to the mainstream of national development is a direct consequence of frequent power blackouts and, in certain cases, a lack of grid connection altogether. Lucrative features of smart grid are not fully incorporated into the power network yet, but policy-makers are paying attention to increase RES reliance. A comprehensive study describing the renewable energy potential of Pakistan is of importance. This research work attempts to present a collective summary of Pakistan’s renewable energy potential. A statistical analysis of the proposed and installed projects in various districts are presented. This paper elaborates the pressing needs of renewable energy integration for resolving Pakistan’s energy crisis. Renewable energy projects are acclaimed in this paper for affording higher living standards and better job opportunities than the fossil fuel based industry in Pakistan. Integrating RESs into the national portfolio is guaranteed to offer profound socio-economic benefits to Pakistan’s rural population.

Abstract:The increasing integration of renewable energy sources into current power systems has posed the challenge of adequately representing the statistical properties associated with their variable power generation. In this paper, a novel procedure is proposed to select a proper synthetic time series generation model for renewable energy sources to analyze power system problems. The procedure takes advantage of the objective of the specific analysis to be performed and the statistical characteristics of the available time series. The aim is to determine the suitable model to be used for generating synthetic time series of renewable energy sources. A set of indicators is proposed to verify that the statistical properties of synthetic time series fit the statistical properties of the original data. The proposal can be integrated into systematic tools available for data analysis without compromising the representation of the statistical properties of the original time series. The procedure is tested using real data from the New Zealand power system in a mid-term analysis on integrating wind power plants into the power system. The results show that the proposed procedure reduces the error obtained in analyzing power systems compared with reference models.

Abstract:As the power control technology of wind farmsdevelops, the output power of wind farms can be constant,which makes it possible for wind farms to participate inpower system restoration. However, due to the uncertaintyof wind energy, the actual output power can’t reach aconstant dispatch power in all time intervals, resulting inuncertain power sags which may induce the frequency ofthe system being restored to go outside the security limits.Therefore, it is necessary to optimize the dispatch of windfarms participating in power system restoration. Consideringthat the probability distribution function (PDF) oftransient power sags is hard to obtain, a robust optimizationmodel is proposed in this paper, which can maximize theoutput power of wind farms participating in power systemrestoration. Simulation results demonstrate that the securityconstraints of the restored system can be kept withinsecurity limits when wind farm dispatch is optimized bythe proposed method.

Abstract:Although wind and solar power is the major reliable renewable energy sources used in power grids, the fluctuation and unpredictability of these renewable energy sources require the use of ancillary services, thereby increasing the integration cost. This study proposes a wind, solar, and pumped-storage cooperative (WSPC) model that can be applied to large-scale systems connected to dispersed renewable energy sources. This model provides an optimized coordinated bidding strategy in the day-ahead market, along with a method to facilitate revenue distribution among participating members. This model takes advantage of the natural complementary characteristics of wind and solar power while using pumped storage to adjust the total output power. In the coordinated bidding strategy, a proportion of the energies is provided as firm power, which can lower the ancillary service requirement. Moreover, a multi-period firm power-providing mode is adopted to reflect the wind-solar output characteristics of each period accurately. The duration of each period is selected as a variable to accommodate seasonal characteristics. This ensures that the provision of firm power can maintain a high proportion under varied connected ratios of wind-solar, thereby obtaining higher revenue. By using the revenue distribution method, the short-term influencing factors of the cooperative model are considered to provide the economic characteristics of wind farms and photovoltaic stations. In this way, revenue distribution can be fairly realized among the participating members. Finally, the effectiveness and economy of the proposed model are validated based on actual data obtained from the power grid in California, USA.

Abstract:Dynamic instability of decentralized wind energy farms is a major issue to deliver continuous green energy to electricity consumers. This instability is caused by variations of voltage and frequency parameters due to intermittencies in wind power. Previously, droop control and inverter-based schemes have been proposed to regulate the voltage by balancing reactive power, while inertial control, digital mapping technique of proportional-integral-differential (PID) controller and efficiency control strategy have been developed to regulate the frequency. In this paper, voltage stability is improved by a new joint strategy of distribution static compensator (DSTATCOM) six-pulse controller based reactive power management among decentralized wind turbines and controlled charging of capacitor bank. The frequency stability is ensured by a joint coordinated utilization of capacitor bank and distributed wind power turbines dispatching through a new DSTATCOM six-pulse controller scheme. In both strategies, power grid is contributed as a backup source with less priority. These new joint strategies for voltage and frequency stabilities will enhance the stable active power delivery to end users. A system test case is developed to verify the proposed joint strategies. The test results of the proposed new schemes are proved to be effective in terms of stability improvement of voltage, frequency and active power generation.

Abstract:In this paper, a wind energy conversion system (WECS) is presented for the electrification of rural areas with wind energy availability. A three-phase AC-DC converter based on a bridgeless Cuk converter is used for power extraction from the permanent magnet synchronous generator (PMSG). The bridgeless topology enables the elimination of the front-end diode bridge rectifier (DBR). Moreover, the converter has fewer components, simple control, and high efficiency, making it suitable for a small-scale WECS. A squirrel cage induction motor (SCIM) is used to emulate a MOD-2 wind turbine to implement the PMSG-based WECS. A direct-drive eight-pole PMSG is used in this study; thus, a low-input-voltage system is designed. The converter is designed to operate in the discontinuous inductor current mode (DICM) for inherent power factor correction (PFC) and the maximum power point tracking (MPPT) is achieved through the tip-speed ratio (TSR) following. The performance of the developed system is analyzed through simulation, and a 500 W hardware prototype is developed and tested in different wind speed conditions.

Abstract:We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connected wind energy conversion systems (WECSs). WECS is considered based on a doubly-fed induction generator (DFIG). Ferroresonance overvoltage associated with a single-pole outage of the line breaker is mitigated by fast regulating the reactive power using the static compensator (STATCOM). STATCOM controller is introduced, in which two incorporated proportional-integral (PI) controllers are optimally tuned using a modified flower pollination algorithm (MFPA) as an optimization technique. To show the capability of the proposed STATCOM controller in mitigating the ferroresonance overvoltage, two test cases are introduced, which are based on the interconnection status of the power transformer used with the grid-connected DFIGs. The results show that the ferroresonance disturbance can occur for the power transformers installed in the wind farms although the transformer terminals are interconnected, and neither side of the transformer is isolated. Furthermore, as a mitigation method of ferroresonance overvoltage, the proposed STATCOM controller succeeds in improving the system voltage profile and speed profile of the wind turbine as well as protecting the system components against the ferroresonance overvoltage.