Power Grid Frequency Research Articles

Power Grid Frequency Control Improvement Using Pumped Storage Based Se-PSO/LADRC

Power Grid Frequency Control Improvement Using Pumped Storage Based Se-PSO/LADRC

A PLL-Less Fourier Analysis Based Self-Synchronizer for Synchronverter having Uninterrupted Power Supply Capability

With the passage of time, more and more power electronic converters are being integrated in power system. This growing pattern of inertia-less inverters challenges the system frequency and voltage. Synchronverter, that mimics real synchronous generator, is a promising solution of frequency and voltage stability in future power grid. It has inherent capability to remain synchronized with the grid. However, it requires phase tracking of the grid voltage prior to grid connection. Several PLL-less self-synchronization approaches for synchronverter have been proposed by researchers. Existing PLL-less approaches either lack uninterrupted power supply capability during synchronization process or have unwanted delays and uncertainties depending upon certain grid conditions. In this paper, a Fourier Analysis based synchronizer for synchronverter is proposed that (a) ensures uninterrupted power supply capability during synchronization, and (b) presents a fast, and reliable solution of synchronization independent of phase and magnitude differences between the synchronverter and grid voltages. The proposed synchronizer is designed, validated by simulations, and compared with the existing Differential Root Mean Square Voltage (DRMSV-) based approach. Results have shown that the proposed synchronizer has improved the speed and certainty of synchronverter self-synchronization under adverse grid conditions.

Inertia control method of direct drive permanent magnet wind turbine under high wind power permeability

Direct-drive permanent magnet wind turbine has high power generation efficiency, especially in low wind speed environment, and is widely used for wind power generation. Direct-driven permanent magnet wind turbines show no inertia response to the system through the grid connection of full-power converters, resulting in increased frequency fluctuation, poor response effect and reduced stability time of the system under sudden load and sudden wind speed conditions. Based on this, an inertia control method of direct-drive permanent magnet wind turbine under high wind power penetration is proposed, and the model of direct-drive permanent magnet wind turbine is built by designing functional modules to improve the synchronous control effect under high wind power penetration. The vector control calculation method is used to design the virtual inertia control parameters, and the decoupling quantity is introduced to decouple the parameters with filter inductance, so as to improve the supporting capacity of power grid frequency fluctuation. The simulation results show that the proposed method has a fast frequency response under sudden load change, and it drops to the lowest value of 49.16 Hz at 12.14 s. Under the condition of sudden change of wind speed, the system frequency rises to the highest value of 50.38 Hz at 12.94 s. It is proved that the proposed method has a certain suppression effect on the amplitude of frequency change, effectively shortens the time for the system frequency to return to steady state, and thus has more advantages.

Design Optimization of Improved Fractional-Order Cascaded Frequency Controllers for Electric Vehicles and Electrical Power Grids Utilizing Renewable Energy Sources

Recent developments in electrical power grids have witnessed high utilization levels of renewable energy sources (RESs) and increased trends that benefit the batteries of electric vehicles (EVs). However, modern electrical power grids cause increased concerns due to their continuously reduced inertia resulting from RES characteristics. Therefore, this paper proposes an improved fractional-order frequency controller with a design optimization methodology. The proposed controller is represented by two cascaded control loops using the one-plus-proportional derivative (1 + PD) in the outer loop and a fractional-order proportional integral derivative (FOPID) in the inner loop, which form the proposed improved 1 + PD/FOPID. The main superior performance characteristics of the proposed 1 + PD/FOPID fractional-order frequency controller over existing methods include a faster response time with minimized overshoot/undershoot peaks, an ability for mitigating both high- and low-frequency disturbances, and coordination of EV participation in regulating electrical power grid frequency. Moreover, simultaneous determination of the proposed fractional-order frequency controller parameters is proposed using the recent manta ray foraging optimization (MRFO) algorithm. Performance comparisons of the proposed 1 + PD/FOPID fractional-order frequency controller with existing PID, FOPID, and PD/FOPID controllers are presented in the paper. The results show an improved response, and the disturbance mitigation is also obtained using the proposed MRFO-based 1 + PD/FOPID control and design optimization methodology.

Design and analysis for chemical process electrification based on renewable electricity: Coal-to-methanol process as a case study

Electrification of traditional large-scale chemical industry based on renewable electricity can greatly reduce process CO2 emission, and store intermittent renewable electricity into chemical products locally to decrease power grid frequency regulation caused by fluctuating renewable electricity. This study presents a framework for electrification of chemical industry from indirect and direct aspects using the state-of-art coal-to-methanol process as a case study. Traditional coal-to-methanol (Process 1) suffers from high CO2 emission due to mismatch of H/C ratio between coal and methanol. A pulverized coal gasification-integrated SOEC process (Process 2) has been investigated, the water–gas-shift unit is avoided and a simplified acid gas removal process is implemented to replace traditional acid gas removal unit in Process 2. Electric heaters and heat pump system are applied in Process 2 as direct electrification methods to form semi-electrified scenario (Process 3). To discuss the effect of electrification levels on process performances, a fully electrified process (Process 4) is also designed. The results show that: CO2 emissions of the four processes are 2.19, 0.71, 0.52 and 0.63 t/t MeOH, and energy efficiency are 57.40 %, 62.32 %, 64.31 % and 57.63 %, respectively. Production costs are 159.1, 294.3, 301.0 and 358.3 $/t MeOH, IRRs are 14, 31, 29 and 14.5 %, respectively. Through this research and analysis, we hope to explore integration potential of renewable electricity and traditional chemical industry, and design a greener methanol production route based on renewable electricity.

Low-Frequency Defense Strategy for Wind Turbine Participating in Power Grid Frequency Adjustment

With the continuous increase of wind power permeability, the dynamic behavior of the power system also changes, which also has a great impact on the setting of the low-frequency load-shedding scheme. The original low-frequency load-shedding scheme has no good adaptability to the system of high-permeability wind power. So, this article analyzes the principles of wind turbines in power grid frequency control. This paper expounds on the principle of low-frequency load-shedding strategy in the power system configuration. Connecting with the actual operation of the grid simulation, simulation results show that wind turbines in power grid frequency modulation can significantly reduce the low-frequency load shedding process of loads and wind power in frequency modulation of low-frequency with a positive impact.

Research on Wind Power Prediction Based on A Gated Transformer

Wind power, as a type of renewable energy, has received widespread attention from domestic and foreign experts. Although it has the advantages of cleanliness and low pollution, its strong randomness and volatility can bring disadvantages to the stable operation of the power grid. Accurate power prediction can avoid the adverse effects of wind power, and is of great significance for power grid frequency regulation, peak shaving, and energy improvement. However, traditional wind power prediction methods can only achieve accurate predictions in the short term and perform poorly in medium- to long-term prediction tasks. To address this issue, a power prediction model based on a Gated Transformer is proposed in this paper. Firstly, it can extract features from different types of data sources, effectively capture their correlations, and achieve data fusion. Secondly, gating unit, dilated convolution unit, and multi-head attention mechanism are added to improve the Receptive field and generalization ability of the model. In addition, adding a decoder to guide data prediction further improves the accuracy of prediction. Finally, experiments are carried out with the data collected from typical wind farms. The results show that the proposed Gated Transformer achieves consistent state-of-the-art results in prediction tasks on different time scales.

Dynamical Model for Power Grid Frequency Fluctuations: Application to Islands With High Penetration of Wind Generation

We study the effects of a high share of wind generation on the frequency fluctuations of power grids on islands. We propose a dynamical model that includes conventional and variable renewable generation, as well as demand variations. Our model can assimilate load and generation data and reproduce frequency fluctuations with the current power mix with a high degree of accuracy, and it allows to simulate the frequency dynamics for different scenarios with a very high penetration of renewable energy. As a case study, we analyze the power grid of Gran Canaria island. We characterize the frequency fluctuations and propose a method to estimate the control needed to keep frequency deviations within reasonable limits.

VSC-HVDC control without PLL for unbalanced grid

When unbalanced faults such as single-phase voltage drop occur in the power grid, VSC-HVDC will fail or become unstable due to sudden changes in amplitude, phase, frequency, etc. of the power grid voltage. Therefore, the role of PLL in a non-ideal power grid is particularly important, but often PLL needs to make a compromise between dynamic response and system stability. Therefore, this paper proposes a free-PLL control strategy under non ideal power grid. First, according to the power transmission model of VSC-HVDC under power grid imbalance, the control command required by the inverter is given, which is determined in the environment free-PLL. Therefore, PLL is not required to retrace the phase of the grid voltage. In addition, in order to overcome the impact of the sudden change of power grid frequency on the free-PLL strategy, a frequency locking strategy is proposed in the free-PLL environment, the response time is about 1 grid cycle. Finally, in order to verify the effectiveness and correctness of the proposed strategy, the VSC-HVDC system’s active power transmission stability is guaranteed when the grid voltage encounters different degrees of single-phase sags.

Utilizing controlled plug-in electric vehicles to improve hybrid power grid frequency regulation considering high renewable energy penetration

This study proposes an incorporated strategy based on energy storage systems (ESSs) like plug-in electric vehicles (PEVs) with load frequency control (LFC) to enhance the frequency stability during high penetration of renewable energy sources (RESs). Furthermore, an innovative-cascaded controller is used in the LFC loop, and PEVs are considered in the two identical areas' multi-source power grids. The proposed control structure is based on using two terms, the first term is the fractional-order-proportional-derivative (FOPD), and the second cascaded term is a fractional-order-proportional-integral (FOPI) to form the cascaded (FO-(PD-PI)) controller. Additionally, the gains of the proposed controller are well designed, utilizing an improved version of the manta ray foraging optimization algorithm (MRFO) labeled as leader MRFO (LMRFO). The effectiveness of the proposed FO-(PD-PI) controller based on the LMFRO algorithm is validated by comparing its performance with that of other control approaches such as (i.e., the proportional-integral-derivative (PID) controller, the tilt-integral-derivative (TID) controller, and the fractional-order-PID (FOPID) controller) based on different optimizers. Different load perturbation patterns, a high penetration level of RESs, and the communication delay time are broadly implemented for ensuring the superiority of the proposed controller in penalizing the power grid perturbations. Furthermore, for validating the efficiency of the proposed controller, an IEEE 39 bus is used. As a result, the proposed integrated strategy is a viable and effective control scheme for modern power grids with high-RESs penetration.

Harmonic Suppression Strategy of LCL Grid-Connected PV Inverter Based on Adaptive QPR_PC Control

To reduce the influence of voltage harmonics on the grid current, a control strategy based on adaptive quasi-proportional phase compensated resonance (QPR_PC) is proposed. Firstly, the LCL grid-connected photovoltaic inverter system model is established, and the stability performance of the three-level inverter system under double closed-loop control is analyzed using the output impedance model of the inverter. Then, a QPR regulator for the zero steady-state error tracking of AC signals is studied. To solve the problem that the system has poor robustness against frequency changes when the traditional QPR regulator is used in the static coordinate system, this paper improves the traditional QPR regulator to optimize the response characteristics of the closed-loop system. Based on the QPR regulator, a phase margin compensation structure is introduced to form QPR_PC control. Then adaptive frequency design is added to ensure good control even when the power grid frequency drifts, which is the control strategy proposed in this paper. Verification shows that the proposed method improves the phase margin of output impedance at a specific frequency, restrains the interference of the 3rd, 5th, and 7th harmonics of grid voltage, and improves the dynamic performance of the system and the quality of grid-connected current. Finally, the simulation results show that the total harmonic distortion rate of grid-connected current is reduced by 1.03% after adopting this strategy, which verifies the effectiveness and correctness of the proposed method.

On the effect of an ANC system towards the transient pressure fluctuations caused by smart-grid controlled centrifugal pumps

Smart-grid control aims to use current power converter technology of pump drives for grid stabilization. Hereby, fluctuations of the power grid frequency are transmitted to the pump drive resulting in pump speed changes. Along with the inherent impeller design these pump speed changes are resulting in pressure pulsations which propagate as hydro acoustic pressure waves throughout the pump system causing noise and vibration issues in the piping system. Therefor, in order to realize smart-grid control, a solution must be found to attenuate or counteract these hydro acoustic pressure waves. In an earlier work [1], an active noise control (ANC) system to reduce pressure pulsations at a pump’s blade passing frequency (BPF) was published with the focus on constant points of operation. However, utilizing smart-grid control will results in high gradients of the pump speed and constantly changing points of operation are to be expected. This paper aims to attack those kinds of operating conditions. Within this paper, moving frequencies of interest at different pump speed gradient with and without active attenuation are analyzed and extracted from time series data by means of Vold-Kalman order tracking filter. In relation to possible fluctuations in the power grids frequency, the active attenuation performance of the ANC system is evaluated.

Energy management strategy of Battery Energy Storage Station (BESS) for power grid frequency regulation considering battery SOX

In recent years, the application of BESS in power system has been increasing. If lithium-ion batteries are used, the greater the number of batteries, the greater the energy density, which can increase safety risks. Considering the state of charge (SOC), state of health (SOH) and state of safety (SOS), this paper proposes a BESS real-time power allocation method for grid frequency regulation. This method establishes the battery charge criterion table, selects the required action unit, and finally solves it through the planning solver. It can realize the safety management of BESS and deal with extreme situations. It can complete a full charge calibration without disconnecting the battery from BESS, so that the SOC of each battery is consistent. The effectiveness of this method is proved by the model based on 50 MW/100 MWh BESS in Qinghai Golmud.

Simulation Study of Improved DDSRF-PLL under Distorted Grid Voltage

When the grid voltage is distorted and harmonic and DC components are mixed, the phase locking accuracy of decoupled double synchronous reference frame for phase-locked loop (DDSRF-PLL) will be greatly reduced. This paper proposes an improved DDSRF-PLL(IDDSRF-PLL) structure based on Frequency Adaptive Sliding Discrete Fourier Transform (FASDFT) filtering. A cascade SDFT structure is adopted for FASDFT filtering. The SDFT with fixed sliding window width at the front stage extracts the fundamental wave signal of power grid voltage to eliminate the influence of harmonics and DC components. The latter SDFT detects the sliding window width of power grid frequency update in real time through a nonlinear tracking differentiator (TD) to suppress spectrum leakage. Then DDSRFT-PLL is used to separate the positive and negative sequence of the fundamental signal and lock the phase. Finally, the simulation results in Matlab/Simulink verify the correctness and effectiveness of the proposed method.

Grid-Vehicle-Grid (G2V2G) Efficient Power Transmission: An Overview of Concept, Operations, Benefits, Concerns, and Future Challenges

Electric vehicles (EVs) are proportionally increasing day-by-day with the inclusion of upgraded technology toward considered zero carbon emission efforts. To mitigate greenhouse gas emissions from the transportation sector, grid-to-vehicle (G2V) and vehicle-to-grid (V2G) technologies are getting significant attention nowadays. EVs equipped with modern technology can help to stabilize the power grids through load-balancing topology during peak hours. The improvement in EVs can support the surroundings in numerous ways, such as power grid voltage and frequency regulations, harmonics distortions, accessible solar energy implemented to the grids, and peak load stabilizations. This literature review analyzes G2V and V2G impacts in more depth, namely opportunities, improvements in strategies, operation, control, issues, and new technology adoptions. This paper emphasizes the possibilities of bringing advancements in EV technology, smooth operations between grids and EVs, fast bidirectional charging and discharging scopes, control of grids and EVs structures, issues, benefits, pitfalls, challenges, and recommendations.

Voltage and frequency stabilization control strategy of virtual synchronous generator based on small signal model

Power system with large scale Inverter-based Resources (IBR) penetration is challenged with insufficient voltage and frequency support capacity. This paper restructures the control blocks of virtual synchronous generator (VSG) from the perspective of traditional synchronous generators’ control, the control path of the system over its active and reactive power output is clarified and simplified, which has facilitated the tuning of virtual inertia and damping parameters. Firstly, the small signal model of VSG control IBR is established, including instantaneous power calculation module, LC filter and power loop, voltage and current loops. In the meantime, the improved VSG voltage and frequency regulation control strategy is proposed based on the stability analysis of the small signal model. The stable operation range of the VSG control grid-connected inverter system is studied with the objective to improve the stability and robustness of the VSG-controlled grid-connected inverter system. Finally, MATLAB/Simulink simulation verifies the correctness of the proposed VSG’s dynamic model of power grid voltage and frequency regulation. The effectiveness of the restructures of VSG is verified as well. The results show that the control strategy not only improves the inertia of the system, but also enables the IBR to support the frequency and voltage of the system.

Microscopic Fluctuations in Power-Grid Frequency Recordings at the Subsecond Scale

Complex systems, such as the power grid, are essential for our daily lives. Many complex systems display multifractal behavior, correlated fluctuations and power laws. Whether the power-grid frequency, an indicator of the balance of supply and demand in the electricity grid, also displays such complexity remains a mostly open question. Within the present article, we utilize highly resolved measurements to quantify the properties of the power-grid frequency, making three key contributions: First, we demonstrate the existence of power laws in power-grid frequency measurements. Second, we show that below one second, the dynamics may fundamentally change, including a suddenly increasing power spectral density, emergence of multifractality and a change of correlation behavior. Third, we provide a simplified stochastic model involving positively correlated noise to reproduce the observed dynamics, possibly linked to frequency-dependent loads. Finally, we stress the need for high-quality measurements and discuss how we obtained the data analyzed here.

Predicting the power grid frequency of European islands

Modelling, forecasting and overall understanding of the dynamics of the power grid and its frequency are essential for the safe operation of existing and future power grids. Much previous research was focused on large continental areas, while small systems, such as islands are less well-studied. These natural island systems are ideal testing environments for microgrid proposals and artificially islanded grid operation. In the present paper, we utilise measurements of the power grid frequency obtained in European islands: the Faroe Islands, Ireland, the Balearic Islands and Iceland and investigate how their frequency can be predicted, compared to the Nordic power system, acting as a reference. The Balearic Islands are found to be particularly deterministic and easy to predict in contrast to hard-to-predict Iceland. Furthermore, we show that typically 2–4 weeks of data are needed to improve prediction performance beyond simple benchmarks.

Study of the impact of DC distribution network under large-scale electric-powered vehicle access

As a high-standard verdant method of transportation, electric-powered-vehicles have become the development hotspot of the automotive business in recent years. Large scale access to electric-powered vehicles can form a distributed energy storage system, which can improve the operational performance of power grid peak shaving and frequency modulation, and improve the comprehensive utilization efficiency of system energy. But at the same time, large-scale electric-powered vehicles connected to the DC distribution network will have a certain impact on its topology. Therefore, this paper studies the impact of the access location and number of electric-powered vehicles on the network topology and establishes a multi-dimensional evaluation system of the DC distribution network topology. The application of this result can play an evaluation and guidance role in the operation stability of the DC distribution network in the case of large-scale access to electric-powered vehicles.

Economic Valuation of Power Grid Frequency Security and the Participants Share Specification

The increasing penetration of non-synchronous renewable resources has made lots of concerns about frequency security. Therefore, power system studies have tried to address this issue in static and dynamic manners. Although considering the reserve in a static way has the advantage of simplicity, it does not ensure the security. This is indicated in this paper by presenting an extended Economic Dispatch (ED) considering all types of reserves and their practical limitations. Also, integrating numerous dynamic simulations to the problems makes them impractical for large-scale grids. In addition, using estimation methods is not accurate enough due to the simplifications. This paper introduces the Frequency Security Value (FSV) for the first time and proposes its calculation algorithm for a specified schedule based on a Frequency Security Index (FSI). Then, an algorithm is proposed for allocating this FSV to the participants based on their technical values. Also, a sensitivity analysis platform is presented for calculating the effect of various modifications. These concepts may have lots of applications, especially in power grid scheduling considering frequency security and payment of ancillary services. The effectiveness and correctness of the proposed methods and algorithms are demonstrated based on the simulation studies of a real large-scale power grid.