66 research outputs found
Power systems with high renewable energy sources: A review of inertia and frequency control strategies over time
Traditionally, inertia in power systems has been determined by considering all the rotating masses directly connected to the grid. During the last decade, the integration of renewable energy sources, mainly photovoltaic installations and wind power plants, has led to a significant dynamic characteristic change in power systems. This change is mainly due to the fact that most renewables have power electronics at the grid interface. The overall impact on stability and reliability analysis of power systems is very significant. The power systems become more dynamic and require a new set of strategies modifying traditional generation control algorithms. Indeed, renewable generation units are decoupled from the grid by electronic converters, decreasing the overall inertia of the grid. ‘Hidden inertia’, ‘synthetic inertia’ or ‘virtual inertia’ are terms currently used to represent artificial inertia created by converter control of the renewable sources. Alternative spinning reserves are then needed in the new power system with high penetration renewables, where the lack of rotating masses directly connected to the grid
must be emulated to maintain an acceptable power system reliability. This paper reviews the inertia concept in terms of values and their evolution in the last decades, as well as the damping factor values. A comparison of the rotational grid inertia for traditional and current averaged generation mix scenarios is also carried out. In addition, an extensive discussion on wind and photovoltaic power plants and their contributions to inertia in terms of frequency control strategies is included in the paper.This work was supported by the Spanish Education, Culture and Sports Ministry [FPU16/04282]
Frequency control studies: A review of power system, conventional and renewable generation unit modeling
Over the last decades, renewable energy sources have increased considerably their generation share in power systems. As a consequence, in terms of frequency deviations, both grid reliability and stability have raised interest. By considering the absence of a consensual set of models for frequency control analysis, both for the different generation units (conventional and renewables) and the power system itself, this paper provides extensive and significant information focused on the models and parameters for studies about frequency control and grid stability. An extensive analysis of supply-side and power system modeling for frequency stability studies over the last decade is presented and reviewed. Parameters commonly used and assumed in the specific literature for such simulations are also given and compared. Modeling of generation units are described as well, including both conventional and renewable power plants.The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper
Chance-Constrained Day-Ahead Hourly Scheduling in Distribution System Operation
This paper aims to propose a two-step approach for day-ahead hourly
scheduling in a distribution system operation, which contains two operation
costs, the operation cost at substation level and feeder level. In the first
step, the objective is to minimize the electric power purchase from the
day-ahead market with the stochastic optimization. The historical data of
day-ahead hourly electric power consumption is used to provide the forecast
results with the forecasting error, which is presented by a chance constraint
and formulated into a deterministic form by Gaussian mixture model (GMM). In
the second step, the objective is to minimize the system loss. Considering the
nonconvexity of the three-phase balanced AC optimal power flow problem in
distribution systems, the second-order cone program (SOCP) is used to relax the
problem. Then, a distributed optimization approach is built based on the
alternating direction method of multiplier (ADMM). The results shows that the
validity and effectiveness method.Comment: 5 pages, preprint for Asilomar Conference on Signals, Systems, and
Computers 201
Load Forecasting Based Distribution System Network Reconfiguration-A Distributed Data-Driven Approach
In this paper, a short-term load forecasting approach based network
reconfiguration is proposed in a parallel manner. Specifically, a support
vector regression (SVR) based short-term load forecasting approach is designed
to provide an accurate load prediction and benefit the network reconfiguration.
Because of the nonconvexity of the three-phase balanced optimal power flow, a
second-order cone program (SOCP) based approach is used to relax the optimal
power flow problem. Then, the alternating direction method of multipliers
(ADMM) is used to compute the optimal power flow in distributed manner.
Considering the limited number of the switches and the increasing computation
capability, the proposed network reconfiguration is solved in a parallel way.
The numerical results demonstrate the feasible and effectiveness of the
proposed approach.Comment: 5 pages, preprint for Asilomar Conference on Signals, Systems, and
Computers 201
Power-Smoothing Scheme of a DFIG Using the Adaptive Gain Depending on the Rotor Speed and Frequency Deviation
In an electric power grid that has a high penetration level of wind, the power fluctuation of a large-scale wind power plant (WPP) caused by varying wind speeds deteriorates the system frequency regulation. This paper proposes a power-smoothing scheme of a doubly-fed induction generator (DFIG) that significantly mitigates the system frequency fluctuation while preventing over-deceleration of the rotor speed. The proposed scheme employs an additional control loop relying on the system frequency deviation that operates in combination with the maximum power point tracking control loop. To improve the power-smoothing capability while preventing over-deceleration of the rotor speed, the gain of the additional loop is modified with the rotor speed and frequency deviation. The gain is set to be high if the rotor speed and/or frequency deviation is large. The simulation results based on the IEEE 14-bus system clearly demonstrate that the proposed scheme significantly lessens the output power fluctuation of a WPP under various scenarios by modifying the gain with the rotor speed and frequency deviation, and thereby it can regulate the frequency deviation within a narrow range
The Impact of Transformer Winding Connections of a Grid-Connected PV on Voltage Quality Improvement
In this paper, a high-power PV power plant is connected to the weak grid by means of a three-phase power transformer. The selection of transformer winding connection is critical especially when the PV inverter has a reactive power controller. In general, transformer winding connection can be arranged in star-star (with neutrals grounded) or star-delta. The reactive power controller supports voltage regulation of the power system particularly under transient faults. Its control strategy is based on utilizing the grid currents to produce a three-phase unbalanced reactive current with a small gain. The gain is determined by the system impedance. Simulation results exhibit that the control strategy works very well particularly under disturbance conditions when the transformer winding connection is star-star with both neutrals grounded. The power quality in terms of the voltage quality is improve
Power quality improvement utilizing photovoltaic generation connected to a weak grid
Microgrid research and development in the past
decades have been one of the most popular topics. Similarly, the
photovoltaic generation has been surging among renewable
generation in the past few years, thanks to the availability,
affordability, technology maturity of the PV panels and the PV
inverter in the general market. Unfortunately, quite often, the PV
installations are connected to weak grids and may have been
considered as the culprit of poor power quality affecting other
loads in particular sensitive loads connected to the same point of
common coupling (PCC). This paper is intended to demystify the
renewable generation, and turns the negative perception into
positive revelation of the superiority of PV generation to the power
quality improvement in a microgrid system. The main objective of
this work is to develop a control method for the PV inverter so that
the power quality at the PCC will be improved under various
disturbances. The method is to control the reactive current based
on utilizing the grid current to counteract the negative impact of
the disturbances. The proposed control method is verified in PSIM
platform. Promising results have been obtaine
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