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The highly random and characteristics of wind power generation challenge the power quality of the wind–hydro complementary generation system (WHCGS). Herein, the transient characteristics of power quality under the complementary generating mode are studied. First, a nonlinear hydropower system (HPS) model is innovatively established considering the dynamic characteristics of hydrounits under part load operation, and then a wind power system model including wind speed model, wind turbine and its controller, generator and converter is established. Finally, the applicability of WHCGS model in power quality evaluation is established and verified by IEEE‐9 node model. Combined with active power, frequency, and voltage power quality indicators, the effects of wind–hydro capacity ratio and voltage sag on the system are quantified. The results show that the increase in wind power penetration will deteriorate the power quality of WHCGS. Moreover, when the wind power capacity reaches 60 MW, it will damage the voltage and frequency stability of HPS. Besides, the larger the voltage sag amplitude, the worse the power quality of WHCGS. The longer the voltage sag lasts, the higher the risk of WHCGS instability. This article provides a technical reference for the safe and stable operation of WHCGS. [ABSTRACT FROM AUTHOR]

The harmonics exacerbated by the integration of distributed energy such as wind power has been extensively studied. However, the interaction and propagation mechanism between harmonic sources in the hydro-wind complementary generation system are still not clear. To tackle this challenge, the presented study establishes the hydro-wind complementary generation system model and explores the harmonics propagation and interaction in all components. Then three operation mode of complementary system (scenario 1: stand-alone Hydroelectric Generating System, scenario 2: stand-alone Wind Farm (WF) and scenario 3: complementary generation system) are selected. The results demonstrate that the integration of HGS diminishes the harmonic at DFIG side but at the grid side. In complementary generation system, the THD u rises but the corresponding THD i declines due to the regulation of power grid. Furthermore, the odd harmonics interactions analysis reveal that the doubly-fed induction generator's (DFIG) side and the stator's side are the two high-risk sources in the complementary generation process. The presented results provide a basis for power quality evaluation of hydro-wind complementary generation system. • Exploit the effect of harmonic propagation on safety of multi-energy power grid. • Reveal the relationship of harmonic property and hybrid grid with/without wind farm. • Present a new model of power system integrating with wind farm and hydropower system. • The implemented methodology provides insights for reliable operations of energy mix. [ABSTRACT FROM AUTHOR]

Seasonal pumped storage (SPS) is a sustainable and effective energy storage solution that can mitigate the seasonal fluctuations of renewable energy sources and provide flexibility to power systems. Despite its huge potentials, the operational mechanism of SPS, particularly for the multi-energy complementary operation, remains poorly understood. In this paper, we propose an optimal scheduling model of a regional power system with SPS and evaluate its potential contribution to energy efficiency, power system stability, and environmental impact. A case study in Qinghai, China, demonstrated that SPS effectively managed seasonal fluctuations of renewable energy sources, improved hydropower generation during the dry season, and stored excess power from renewable energy sources and the main power grid. Furthermore, our analysis revealed that SPS significantly improved energy efficiency compared to traditional pumped storage by increasing system energy efficiency by 11.21%, reducing wind and solar power by 72.97%, and lowering carbon emissions by 94.41%. Overall, SPS has immense potential in providing power system flexibility and enhancing the decarbonization of power systems. [Display omitted] [ABSTRACT FROM AUTHOR]

The penetration of multiple integrated renewable energies to the power grid are relevant for decision making in energy policy, environment and business. Such an electricity penetration is affected by the intermittent and volatile characteristics of integrated energies, mostly significantly related to the safe and stable electricity production and supply in real world. Here, this paper focuses on the low frequency oscillation analysis of the hydropower generation response to the wind and solar variability. To enable this analysis, a hybrid model of hydropower system integrating with the wind and solar power system is presented. The Nyquist and root-locus stability methods are used to investigate the sensitivity performance of the hydropower governor to the fluctuation of the integrated renewable energies. Additionally, to quantify the risk of the hybrid system, the low frequency oscillation response of hydropower system to wind/solar/hydropower quota and transmission line distance ratio is extensively investigated in this study. The results show that under the case of the wind, solar and hydropower ratio is 40:1:150, the optimal values for maximally reducing hydropower low frequency oscillation are finally determined as kp = 0.8, ki = 0.25 and kd = 0.5. Regarding a certain wind/solar/hydropower quota, it is a promising strategy to increase the solar-load transmission line in order to achieve the safe and stable operation of the hybrid system and a relatively excellent dynamic regulation capacity of the hydropower governor. The model, methods and results implemented in this study are exploited to markedly improve new knowledge applications, policy management, low carbon emissions and investment competitiveness of future energy systems. [ABSTRACT FROM AUTHOR]

• Define and quantify hydropower flexibility in power regulation and frequency response. • Flexibilities are coordinated in day-ahead scheduling of hydro-wind hybrid power system. • Benefits and costs of hydropower providing flexibility. • Suggested schemes weighing benefits and costs under different capacity ratios. Uncertainty and instantaneous volatility of wind power make it crucial to schedule the hydropower scientifically to supply flexibility at multiple timescales in renewable energy hybrid power generation systems (RHPS). However, current day-ahead scheduling strategies do not consider the flexibility of time scales below the minimum scheduling time resolution, resulting in insufficient flexibility in intraday operation, power curtailment and load loss. Therefore, in this paper, day-ahead scheduling model coordinating power regulation flexibility (PRF) at 15 min timescale and frequency response flexibility (FRF) at seconds timescale is proposed for hydro-wind hybrid power generation system (HWHPS). Meanwhile, the ability, benefits, and costs of hydropower on supplying flexibility in HWHPS are studied in detail. First, the demand and supply for PRF and FRF are defined and quantified at different confidence levels considering the regulation characteristics of hydropower units. Then, a heuristic piecewise method is utilized to linearize the nonlinear FRF expression, and a day-ahead scheduling MILP model of the HWHPS is constructed. The MILP model is applied to a HWHPS composed of a hydropower station in southwest China and a virtual wind farm simulated based on the data representative for the hydropower station region. We found that the available hydropower flexibility has potential in reducing the maximum frequency deviation, wind power curtailment and load loss. Meanwhile, hydropower provides flexibility at the cost of hydro energy loss due to increased water consumption, especially for supplying FRF during periods of high wind penetration. Finally, since benefits and costs are affected by different confidence levels, a comprehensive index is proposed to evaluate different capacity ratios and scenarios to suggest confidence levels for day-ahead scheduling. Decision makers can also refer to the flexibility supply capacity of hydropower station to select the connected wind power capacity and system load to ensure comprehensive benefits. The methods, models and conclusions in this study can provide a valuable reference for the planning and dispatching of HWHPS, which contributes to the reliability and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A vibration avoidance strategy considering the multiple vibration factors is proposed. • The influences difference of wind and solar energy on hydropower units are analyzed. • The planned output schemes of cascade hydropower station are presented. The cascade hydro-wind-photovoltaic complementary generation system is considered to be an effective approach to solve the output fluctuation of renewable energy. However, for hydropower units, grid-connected operation results in frequent power adjustments and increases the risk of operating in vibration zones, which may lead to the low generation efficiency and hidden danger for the power plant. This study proposes a vibration avoidance strategy based on the unit commitment while considering multiple vibration factors. Multi-objective optimization is performed to minimize the water consumption, the number of times crossing the vibration zone and the number of units involved in regulation. Results for a case study located in the Southwest China, indicate that the proposed strategy avoids hydropower units operating in the vibration zone (the vibration rates decrease from 7.6%, 6.7%, 6.3% to 0 under three initial water levels). Comparing 9 scenarios with different meteorological conditions, indicates that photovoltaic power enables less hydropower units to complete the peak load regulation and to cross the vibration zone less frequently due to PV daily generation profile fitting better the load curve, unlike wind power. Finally, the operation schemes of cascade hydropower station in different periods are proposed. The suggested models are beneficial in reducing the impact of the vibration on hydropower units in hybrid power system and provide operation strategy for cascade hydropower station. [ABSTRACT FROM AUTHOR]