Grid Frequency Control Research Articles

The primary frequency modulation control strategy based on fuzzy active disturbance rejection control for gas turbines

Gas turbines play a core role in clean energy supply and construction of comprehensive energy system, and the control performance of primary frequency modulation (PFM) of gas turbine has a great impact on the frequency control of the power grid. However, there are some control difficulties in the PFM control of gas turbines, such as the coupling effect of fuel control loop and speed control loop, slow tracking speed and large variation of operating conditions. To relieve the above difficulties, a control strategy based on the fuzzy-modified active disturbance rejection control (F-MADRC) proposed in this paper. Based on the analyses of the parameter stability region for active disturbance rejection control (ADRC), fuzzy tuning rules of parameters for F-MADRC are designed. Finally, the proposed F-MADRC is applied to the PFM system of MS6001B heavy-duty gas turbine. The simulation results show that the gas turbine unit with the proposed method can obtain the best control performance of the PFM with strong ability to deal with system uncertainties. The proposed method shows good engineering application potential.

Sub-Synchronous Oscillation Constrained Communication-Free Grid Frequency Control of Offshore Wind Farm Linked HVDC System

This paper proposes a frequency control method of a voltage source converter (VSC) high-voltage direct current (HVDC) system for large-scale offshore wind farms (OWFs) integration into an AC grid. Without frequency control, power output of OWFs varies with the wind velocity and it causes a grid frequency fluctuation. This fluctuation on the AC grid is becoming more severe as the level of wind power penetration increases. The previously suggested communication-free controls are vulnerable to continuously changing frequency fluctuations owing to concerns about its excessive energy releases. Therefore, our proposed control enables OWFs with HVDC to participate in grid frequency regulation continuously by considering its energy state when AC grid frequency fluctuates. In addition, there is a concern about sub-synchronous oscillation (SSO) instability owing to its cascading frequency control structure. A simplified small-signal model is developed to reveal out the existence of these SSO problems and its main factors in the frequency control scheme. Using developed model, overall system stability is comprehensively investigated. Also, a damping controller to mitigate SSO instability is also suggested and validated through simulation. To demonstrate the effectiveness of overall proposed frequency control, time-domain simulations were also carried out utilizing PSCAD/EMTDC under varying wind velocity condition.

Design Optimization of a Horizontal Particle Receiver for a Modular Beam Down Receiver CSP

CSP research is focused on increasing the economic competitiveness of this technology as compared to conventional and emerging energy generators. Higher temperature operation conditions represent a pathway toward cost reductions since they enable a relatively smaller solar field area (typically ~40-50% of the plant cost) for the same electrical output. For example, supercritical CO2 power cycles with solid particles as the HTF could enable >600°C operations and a ~50% power bloc cycle efficiency (considerably higher than steam cycles, <40%). Additionally, small modular systems could increase competitiveness through reduced financial risk, increased system flexibility, and the value of additional services that a modular CSP could offer to the electricity grid (frequency control, peaking supply, etc.). This study investigates the Beam Down Receiver (BDR) configuration as a design that could be well-suited to meet these goals while also overcoming some of issues with particle receivers, such as particle attrition, advective losses, and operation control. In particular, this work introduces a novel horizontal particle receiver (HPR) and analyzes the main design parameters, including tower height, BDR size, radiation flux on the receiver, and receiver nominal power. The analysis shows that tower heights between 35m to 60m are ideal for high temperature receiver capacities of 8-15 MWth, and that this configuration can achieve a minimized LCOH of ~24 USD/MWth. These results suggest that BDRs combined with particle mediums could represent a viable high temperature, high efficiency CSP alternative.

Assessment of High Wind Power Permeability Power System Frequency Regulation

Global wind power has expanded quickly in recent years to help with the energy issue and environmental degradation. The large-scale integration of wind power has become a hot topic for academic research in recent years due to the potential to improve the stability of the power system through the application of wind power participation in power grid frequency control. This study reviews the research on power system frequency regulation approach with high wind power permeability and classes the frequency control difficulties of wind power integration. A review and analysis are conducted on the energy storage system that is involved in the frequency management of the power system with high wind permeability.

Utilizing grid‐supportive load response to shape resilient frequency control of the power grid

AbstractThe increasing penetration of renewable energy sources and the retirement of conventional generation units have decreased system inertia, making power systems more vulnerable to resilience and stability issues. To address this problem, this paper proposes a novel approach using grid‐supportive loads (GSLs) to provide a fast and concise primary frequency response and a deep deterministic policy gradient agent‐based secondary controller to restore the system frequency to the nominal value. The proposed method is evaluated on the single‐area and multi‐area test systems. The simulation results demonstrate that using GSLs enhances the power system's stability and resilience. Compared to conventional controllers, the frequency nadir is improved with GSLs. Additionally, the proposed method effectively enhances resilience even with high penetration. These findings indicate that the proposed approach can improve the resilience and stability of power systems and provide a promising solution for future power systems. The results of this study underscore the importance of utilizing innovative approaches to enhance the stability and resilience of power systems in the context of high penetration of renewable energy sources and the retirement of conventional generation.

Multi-objective distributed control of WT-PV-BESS integrated weak grid via finite time containment

This paper proposes a finite time containment control scheme to achieve distributed control of a weak grid which is integrated with photovoltaic (PV), wind turbine (WT) and battery energy storage system (BESS). Taking advantage of the containment control in multi-dimensional control, we proposed a multi-objective control scheme of the WT-PV-BESS system in a weak grid, wherein four control objectives are specified, namely, bus voltage regulation, grid frequency control, peak load shaving and economic benefits optimization for the system operator. Firstly, the sizing approach of BESSs to fulfill the operation mission requirements is proposed; meanwhile, the general coordination strategy for the PV, WT and BESS to achieve the demand–supply balance is proposed. Subsequently, the predefined four control objectives are modeled and transferred into the long/short time frame operational constraints of the BESSs. Afterwards, the finite time containment control algorithm is proposed to force the BESSs into achieving containment status within prescribed time. Simulation case studies are conducted on a modified IEEE 9-bus system to show the effectiveness and performance of the proposed scheme.

Cooperative grid frequency control under asymmetric V2G capacity via switched integral reinforcement learning

In recent years, V2G techniques have been successfully implemented to stabilize frequency deviations in the grid caused by intermittent renewable energy sources. However, the battery capacity constraints and real-time dynamic driving demands of electric vehicles (EVs) in V2G systems hinder the coordination between V2G control and power plant frequency control strategies. It leads to the dynamic asymmetry of regulation up (RU) and regulation down (RD) frequency regulation (FR) capacity of V2G system, which can affect the performance of V2G FR. To cope with this problem, this paper proposes a switched integral reinforcement learning (SIRL) scheme for cooperative grid frequency control. The proposed scheme integrates V2G control with the power plant frequency control, which are cooperated with each other to complete FR tasks. A novel switched neural network (NN) structure is constructed for the training process of the SIRL algorithm to solve the problem of dynamic asymmetric FR capacity. A switched V2G utility function and a global cost function are constructed for RU and RD. Two independent subnetworks with the same structure are adopted for RU and RD learning to optimized V2G control parameters respectively under dynamic asymmetric output constraints. Two case studies of the IEEE 14-bus test system demonstrate the effectiveness and advantages of the proposed scheme.

Profit enhancement and grid frequency control by energy level scheduling of CAES system in wind-connected electrical system

The maintenance of power balance poses significant challenges in renewable combined deregulated power systems due to the unpredictable nature of renewable energy sources. This situation leads to economic instability within the system. However, an energy storage system can help maintain energy supply and control system stability for renewable incorporated thermal power plants. Unlike in regulated markets, energy prices in deregulated markets are not fixed by any government body or particular company. Instead, the Independent System Operator (ISO) serves as the main entity in the electrical market, gathering tenders from Generation Companies (GENCOs), Distribution Companies (DISCOs), and Transmission Companies (TRANSCOs). The market controller regulates energy prices using Nodal Pricing (NP), which provides economic benefits to both GENCOs and DISCOs. However, the unpredictability of renewable sources often results in a decline in system profit due to the production of an imbalance price (CostIMC) caused by a mismatch in contracted power generation from the renewable power plant. To address these issues, this study proposes a novel combined system that utilizes a suitable scheduling technique for the optimum operation of a wind farm-compressed air energy storage (CAES) system to maximize profit and revenue while maintaining grid frequency. The CAES system’s energy level is divided into four different levels, and an optimal strategy has been developed to efficiently utilize the CAES system to maintain grid frequency. This work has been conducted in both regulated and deregulated environments using a modified IEEE 30-bus system. The proposed method has been compared with an existing approach and has yielded better results in all aspects.

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

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

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.

PV system frequency regulation employing a new power reserve control approach and a hybrid inertial response

The integration of photovoltaic (PV) systems into power grids has become a popular way to provide sustainable, low-cost energy. However, the lack of internal inertia in PV systems, as well as the continuous operation of PV plants at maximum power point, might pose challenges for grid stability and frequency control. The commonly employed method to participate in the frequency control is to operate the PV plant in a deloading mode at reduced power. As a result, a virtual inertial and primary frequency control can be provided. However, operation in a deloading mode may require complex algorithm and sensors for irradiation and temperature measurement. In addition, the virtual inertia reliability is dependent on power electronics, processors, and control. This paper presents two alternative techniques for dealing with frequency control. The first one combines simplicity and the absence of irradiance and temperature sensors by using a novel power reserve control (PRC) technique based on PV voltage variation. It has a two-mode cycle, with the first mode being used to calculate and reach the MPPT point and the second mode being used to provide the appropriate power reserve. The cycle continues in PRC mode until a triggering event is generated by an implanted device that captures the PV system’s voltage change. In this study, the PRC approach is applied to offer primary frequency control (PFC) and virtual inertia (VIC). The second technique addresses the lack of real rotational inertia in PV systems. In this paper, we suggest incorporating a synchronous generator into the PV plant without providing active power. Its main role is to offer an intrinsic real inertial response. In addition, a hybrid approach based on virtual and real inertial response is investigated and discussed. To model and simulate the entire system in an isolated and interconnected power grid, Matlab software is employed. Both proposed approaches are tested and validated in the presence of climate changes and large perturbations affecting the grid.

Primary Frequency Control of Wind-solar-storage Power Station Considering Discrete Control Nonlinearity

With the gradual advancement of dual-carbon goals, the wind-solar-storage power station has become the mainstream trend in constructing new energy stations due to their wind energy and luminous complementary characteristics. However, the current research on primary frequency control of new energy stations is still focused on a single-machine strategy. The communication delay and control period caused by long control links are not considered. It is difficult to describe the influence of the difference in dynamic characteristics of wind-solar-storage power on primary frequency control performance. Therefore, this paper takes the multi-layer control link wind-solar-storage power station as the research object, establishes the nonlinear control model considering the influence of control delay and control period, and puts forward the wind-solar-storage power plant primary frequency control method, which is suitable for participating in the frequency control of power grid.

Intelligent load frequency control for improving wind power penetration in power systems

After wind power is connected to the grid, because the power of wind power will fluctuate greatly, the frequency deviation of the grid will increase with access to wind power generation, then the challenge of frequency control in power grid is also increasing. The Load frequency control(LFC) is one of the important components of frequency control, the fluctuation of wind power output of the system will put forward a higher demand for load frequency control (LFC) of the power grid so as to increase the proportion of wind power in the system. In this paper, a PI controller whose parameters are set by an intelligent cloud calculation result is designed for LFC of the interconnected power system with large-scale wind power. The parameters in PI controller are obtained through the cloud model whose inputs are the control error and the corresponding rate of change so as to realize the adaptive tuning. The subordinate cloud parameters are designed considering randomness of wind power, which effectively solves the problems of poor parameter robustness in traditional PI control. The simulation of the two-area interconnection system with wind power is carried out to verify the effectiveness of the proposed method in the case of random wind power.

Impact of the High Penetration of Renewable Energy Sources on the Frequency Stability of the Saudi Grid

The high penetration of inverter-fed renewable energy sources (RESs) in modern energy systems has led to a reduction in the system’s inertial response. This reduction in the rotational inertial response is associated with synchronous generation and might result in a deteriorated frequency response following a power disturbance. This paper investigates the frequency stability of the Kingdom of Saudi Arabia’s (KSA) grid. It includes a description of the changing energy landscape of the KSA’s electricity grid and an investigation of the impact of high penetration levels of inverter-fed RESs on the dynamic behavior of the KSA grid. The impact of RESs has been studied through a simulation of case studies of the future KSA power system using the MATLAB/Simulink simulation software. The frequency stability of the KSA’s power system has been evaluated with various RES levels under peak and base load conditions. The simulation results show that the high penetration levels of RESs dramatically affect the system’s frequency response, especially under off-peak conditions. In addition, the significance of battery energy storage systems (BESSs) for compensating the reduction in the system inertial response has been addressed. The results show the effectiveness of aggregated BESSs for enhancing the system frequency control of the KSA grid.

A New Communication-Free Grid Frequency and AC Voltage Control of Hybrid LCC-VSC-HVDC Systems for Offshore Wind Farm Integration

We propose frequency and voltage control method for a hybrid high-voltage direct current (HVDC) system for integrating an offshore wind farm into transmission networks. Conventionally, DC voltage level is maintained as constant regardless of the wind velocity and the grid frequency, so AC voltage fluctuates with active power variation in a hybrid HVDC system due to the innate reactive power absorption of inverter side line-commutated converter (LCC). However, in the proposed method, the DC voltage changes according to the wind velocity. Furthermore, DC voltage is simultaneously regulated to participate in frequency control in a communication-free manner. These two characteristics can be achieved by using five droop control methods proposed here. Additionally, by determining droop constants using the proposed determination methods, AC voltage can be maintained as constant during active power fluctuations. Therefore, using the proposed method, an offshore wind farm can be stably connected to mainland transmission networks and successfully used as frequency supporting resources, because voltage characteristics of the AC network are not destabilized. A small-signal state-space (SS) model of the target system was also developed to investigate stability of the proposed control. The utility of the proposed method is demonstrated by case studies using PSCAD and SS models.

Use of the Thermal Inertia of Trains for Contributing to Primary Frequency Control and Inertia of Electric Power Systems

The current trend of massively incorporating renewable-based generation into power systems is affecting frequency stability. This generation does not inherently provide inertia owing to its electronic interface. Therefore, many approaches have been proposed to address the problem of inertia weakening. Beyond the new trends of making new generation and storage responsive to grid needs, this study addresses the problem from the role of consumers. The use of railway consumption to contribute to frequency control tasks, without affecting train circulation, is proposed. For the first time, the provision of virtual inertia combined with primary frequency control is presented. This is achieved by means of the power consumption of ventilation and air conditioning systems, while maintaining the thermal comfort of passengers. To illustrate this new concept, a case study of a real metro line is presented. The results demonstrate the benefits of using the thermal inertia of trains to contribute to grid frequency control. Also, some insights into technical requirements and possible issues are provided. An appropriate combination of primary frequency control and virtual inertia can reduce technical requirements and provide better frequency performance.

Power optimization control of VSC-HVDC system for electromechanical oscillation suppression and grid frequency control

The voltage source converter (VSC) based high-voltage DC (HVDC) transmission system usually adopts damping and inertia control to quickly and independently adjust the active- and reactive- power, to improve the frequency stability and suppress the electromechanical oscillations of the power grid. This paper first analyzes the effect of the proportional-derivative (PD) controller parameter on the HVDC output power. The study shows that when the proportional-derivative controller parameter is increased to the limit value, HVDC will operate in the rapid power compensation (RPC) mode. Namely, according to the positive or negative polarities of the rotor speed deviation and the grid frequency deviation, the active- and reactive- power limits are used as the reference to rapidly control the output power, thereby minimizing the system’s unbalanced power, the rotor oscillation, and the frequency fluctuation. To this end, this paper proposes a coordinated active-/reactive- power control strategy for the VSC-HVDC system based on the RPC mode to suppress the grid electromechanical and frequency oscillations. The RPC mode enables HVDC to quickly release/absorb power, to compensate for system’s required power shortage or suppress excess power. When the speed deviation, the frequency deviation, and their rates of change meet the requirements, the damping control is used to make HVDC exit the RPC mode and further enhance the ability of the VSC-HVDC system. Simulation results prove the effectiveness of the proposed power optimization control strategy.

Extended Simplified Electro-Mechanical Model of a Variable-Speed Wind Turbine for Grid Integration Studies: Emulation and Validation on a Microgrid Lab

The energy transition towards renewable energies is crucial for the sustainable development of a society based on hydrocarbons. The current level of penetration and growth of wind energy in electric power systems is evident and many researchers have presented new methods for simulating and representing the electrical and mechanical characteristics of variable-speed wind turbines. However, complete mathematical models developed and implemented, for example, in MATLAB/Simulink® software, require significant computational efforts that could make grid studies impractical when its scale tends to increase. To contribute to facing this issue, this paper proposes an extended simplified model for a variable-speed wind turbine that considers the dynamic behavior of its mechanical system and includes an approximate representation of the power electronic converter. This approach broadens the scope of studies related to grid frequency control and power quality (fast-frequency response, primary frequency control, and voltage control, among others), considerably reducing the computational burden. Several validations of the proposed simplified model are presented, including comparisons with a doubly fed induction generator-based wind turbine model (phasor type) from the MATLAB/Simulink® library, and laboratory experiments under controlled conditions. The results show a good fit of the proposed simplified model to the MATLAB/Simulink® model, with minimal delays about 3% of the wind turbine inertia constant. Moreover, with the proposal, the computational time is reduced by up to 80% compared to a detailed model. This time reduction is achieved without penalizing the numerical accuracy and the estimation quality of the real behavior of the variable-speed wind turbine.

Study of the dynamic performance boundaries of a converter’s energy storage device

Maintaining frequency stability is one of the central objectives of power grid operation. While this task is currently primarily done by employing stored rotational energy, in a converter-dominated grid fed by renewables, sources, such as wind and photovoltaic, must be involved in the frequency control of the power grid in order to maintain a stable, efficient grid operation in the process of achieving carbon neutrality. However, due to the lack of rotational inertia reserves, the converter requires additional energy storage devices to respond to the grid’s frequency regulation requirements. For modeling a converter-dominated grid, the behavior of such additional short-time storage must be modeled properly in order to obtain realistic simulation results, which allow drawing conclusions about the frequency stability behavior of the grid. This paper investigates the boundaries of the dynamic performance of the output current of the energy storage device so that the converter can achieve the function of frequency regulation in a more economical manner. In this paper, a dynamic supporting converter based on a phase-locked loop and a grid-forming converter, as well as the DC link of the converter containing an energy storage system, are modeled. On this basis, the optimal boundaries of the dynamic performance of the output current of the energy storage device are investigated. It is concluded that not only the proper sizing of grid-supporting energy storage devices is important for proper grid operation, but the dynamic behavior also has to be modeled and designed properly in order to guarantee a stable operation under all circumstances.

Impact of Battery Energy System Integration in Frequency Control of an Electrical Grid with Wind Power

The rapid increase in the integration of renewable energy sources into the electrical grid is posing new challenges for the dynamic responses due to the global inertia reduction. In this regard, the impact on frequency stability of such reduction and the potential support from wind power have been investigated lately. However, it is well-known that the variability of wind power and its reduced inertia may not be enough to handle the power unbalance. Energy storage systems (e.g., batteries) may provide the required additional flexibility to ensure proper response. In this paper, an analysis of how the different control loops for frequency support on wind power and batteries interact and perform is presented. To gain insights from the different impacts, a sensitivity analysis comparison for frequency regulation through (i) inertia and droop control of a variable speed wind turbine and (ii) battery is performed. The analysis was carried out through simulations using the well-known 4 generator 2-area model adapted to include a wind farm. From a battery perspective, its ramping capabilities were varied to provide frequency regulation. The paper shows how, depending on the control parameters and battery size, the frequency response may even become unstable due to interactions of the various pieces of technology. Thus, it shows that coordinated actions, control optimization and grid status among different actors on the grid (as battery and wind) is required for stable operation.