Power Reserve Control Research Articles

Hierarchical power reserve control of string-inverter-based photovoltaic power plant for primary frequency control

Retaining a certain power reserve is the precondition for a photovoltaic power plant (PVPP) to provide primary frequency control. Usually, a string-inverter-based PVPP may consist of hundreds of string inverters, and each string inverter has several direct current (DC) input channels. Thus, how to allocate the power reserve among so many controllable units is a challenging problem. In this paper, a hierarchical power reserve control method for a string-inverter-based PVPP to provide primary frequency control is introduced. In the inverter layer, the power reserve of each DC input channel is determined to balance the DC voltage variation of each channel during primary frequency control. In the plant layer, the power reserve is allocated to each PV cluster based on the predicted power generated by long short-term memory (LSTM) network, and the PV clusters are formed based on the historical generated power of each string inverter using K-means method. Furthermore, the string inverters within the same PV cluster evenly share the power reserve. To validate the proposed method, case studies in both the inverter layer and plant layer are carried out; the results verify the effectiveness of the proposed method.

Research on active participation of distributed photovoltsics in power grid primary frequency control strategy

Distributed photovoltaic systems can actively contribute to the primary frequency regulation of the power grid by reserving capacity. Traditional power reduction methods often employ fixed load reduction ratios, potentially resulting in inadequate frequency regulation capacity and unnecessary reserve power. This paper centers on optimizing power reserve control, starting with the construction of a two-stage model for a photovoltaic grid-connected inverter power generation system. It includes the design of a maximum power estimation method and the implementation of photovoltaic power reduction operation. The article proposes a strategy to utilize photovoltaic backup capacity for achieving primary frequency modulation effects in a short time scale. Additionally, it adopts a variable power reserve ratio operation strategy over the long term, aiming to enhance photovoltaic power generation and optimize solar energy utilization without compromising the grid’s frequency and quality. Finally, a MATLAB/Simulink model is developed to validate the effectiveness of the control strategy. Simulation results indicate that the proposed strategy satisfies frequency regulation requirements, enhances power generation efficiency, and improves the economic viability of photovoltaic operations.

A Review of Fast Power-Reserve Control Techniques in Grid-Connected Wind Energy Conversion Systems

Grid-connected power-converter-interfaced systems have been sharing the responsibility of grid generation alongside conventional synchronous generators. However, these systems lack spinning reserves, leading to a decrease in system inertia and resulting in more pronounced frequency deviations during power imbalances. Therefore, grid codes require the active involvement of wind energy conversion systems in frequency control, aiming to constrain the frequency and rate of change of frequency variations within predefined limits. This paper reviews fast power-reserve control techniques without energy storage in wind energy conversion systems that do not depend on frequency or rate of change of frequency values. The resulting effects on system frequency, energy production, mechanical loadings, and electrical loadings are assessed. The techniques are classified in the maximum-power point-tracking region according to the power function during the transient response, such as constant, speed-, time-, or mechanical power-dependent methods. Both overproduction and underproduction stages are considered. Certain techniques are tested on simulation grids that include either hydro or no-reheat steam generators, followed by a comparative analysis.

Power reserve control for utility-scale PV power plants under cloud conditions

The photovoltaic generation growth has posed challenges for the control and operation of contemporary power systems, degrading the system frequency response and stability margins. The decrease of the system equivalent inertia and the performance deterioration of the primary frequency control are the main causes of these problems. Such challenges can be overcome by the provision of ancillary services from photovoltaic power plants. However, the provision of ancillary services based on active power, such as inertial response, frequency regulation, and curtailment, requires the de-loaded operation of the photovoltaic power plants. In such context, this work proposes a de-loaded control approach (or, equivalently, power reserve control) for large photovoltaic power plants under shading conditions caused by cloud movements. This kind of shading condition poses a significant challenge for the de-loaded control, as it causes large and fast variations in the maximum power point of the multiple photovoltaic generation units that compose the photovoltaic power plant. A test system corresponding to a 100 MWac photovoltaic power plant with 25 photovoltaic generation units of 4 MWac is employed to evaluate and validate the proposed control approach. The stochastic distribution and movement of clouds, as well as the solar irradiance over the photovoltaic power plant are generated by an approach based on the fractal geometry. The proposed control was effective and presented a good performance under different cloud coverage levels.

Distributed Power Reserve Control in Grid-Connected Cascaded H-Bridge Converter-Based Photovoltaic Systems

Distributed Power Reserve Control in Grid-Connected Cascaded H-Bridge Converter-Based Photovoltaic Systems

Frequency regulation method for two-stage PV system based on DC voltage coordination

The current frequency regulation methods for a photovoltaic (PV) system cannot balance frequency support and primary control performances. This paper proposes a frequency regulation method for a two-stage PV system by controlling DC voltage, which is coordinated with the enhanced virtual inertia control (VIC) of the DC capacitor. The power reserve control of the PV arrays is improved considering the characteristics of the VIC, thereby strengthening the frequency regulation ability of the PV system. An active DC voltage recovery control is designed at the inverter to restore the frequency support ability after primary frequency control. With MATLAB/Simulink software, the performance of the proposed method in dealing with different load sizes, load change trends, and DC voltage recovery coefficient is verified by comparing it with other traditional methods in different scenarios. The proposed method can fully use the available power to improve the frequency nadir, rate of change of frequency, and voltage recovery ability.

An Improved Photovoltaic Power Reserve Control With Rapid Real-Time Available Power Estimation and Drift Avoidance

An Improved Photovoltaic Power Reserve Control With Rapid Real-Time Available Power Estimation and Drift Avoidance

A Master-Slave-Based Power Reserve Control Approach for Solar PV Participation in Frequency Control

A Master-Slave-Based Power Reserve Control Approach for Solar PV Participation in Frequency Control

Adaptive Power Reserve Control for Photovoltaic Power Plants Based on Local Inertia in Low-Inertia Power Systems

Retirement of thermal power plants and growth in the capacity of power electronics based renewable energy sources reduce the inertia of power systems, making them more sensitive to frequency disturbances. The shortfall of system inertia cannot be compensated by the remaining synchronous generators and alternative solutions are required. Photovoltaic power plants (PVPPs) can provide frequency support services through the application of flexible power point tracking methods and power reserves. This paper proposes a power reserve distribution method based on local inertia across the PVPPs of a power system aimed at enhancing the system frequency response compared to fixed power reserve levels, especially in weaker and less meshed networks. A multi-level adaptive power reserve control for different system inertia levels is also proposed. The performance of the methods against different frequency events is validated through extensive real-time simulations based on benchmark network models.

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.

Cooperative Output Regulation of Large-Scale Wind Turbines for Power Reserve Control

This paper develops a distributed control framework to coordinate large-scale wind turbines for fairly sharing the power reserve request on a wind farm. A cooperative output regulation problem is formulated in a multi-agent framework, where the synchronization of turbine system outputs are established regarding the heterogeneity of turbine models. For this purpose, a homogeneous virtual system is created first and embedded into each turbine to generate the agreed trajectories across the wind farm in a distributed manner. The local power tracking of individual turbines is then enforced by the synthesized output regulator, whose control gains are determined by a variant of the Sylvester equation. The proposed approach issues the generator torque and blade pitch commands in a unified manner and is resistant to wind disturbances. The case studies are carried out through simulations and in a real laboratory-scale distributed communication network. The simulation results demonstrate the effectiveness of coordinated actions of wind turbines in response to the changing demands, under both constant and turbulent wind scenarios with the plug-and-play capability.

Dynamic Reserve Power Point Tracking in Grid-Connected Photovoltaic Power Plants

This paper introduces a dynamic power reserve control methodology called reserve power point tracking (RPPT) for grid-connected photovoltaic (PV) plants. The proposed RPPT methodology is employed to ensure availability of the required power reserve to support the grid and accordingly facilitate high penetration of PV generation in the grid. Implementing this control methodology does not require any extra hardware. The proposed methodology regulates the average PV power dynamically by periodically operating on and off the maximum power point (MPP) in order to inject a constant desired power into the grid. Tracking a desired power reference implies that the proposed methodology, is a form of flexible power point tracking (FPPT). However, unlike a traditional FPPT, the proposed methodology also provides updated information of the available maximum PV power. Hence, the RPPT fulfills both FPPT and maximum power point tracking (MPPT) functionalities simultaneously. The proposed methodology extracts the MPP information and uses this information to calculate and regulate the amount of PV reserve power. One of the main advantages of the proposed algorithm is its applicability under partial shading conditions. Its effectiveness is demonstrated by experimental results under changing solar irradiance, grid frequency deviation and partial shading conditions.

An AI-Based Power Reserve Control Strategy for Photovoltaic Power Generation Systems Participating in Frequency Regulation of Microgrids

In this paper, a novel AI-based power reserve control strategy is proposed for photovoltaic (PV) power generation systems participating in the frequency regulation (FR) of microgrids. The proposed strategy uses a frequency response module to determine the target power reserve ratio of the PV system based on microgrid frequency deviation, as well as a power reserve control module to obtain the target duty cycle, which is input to the BOOST converter. The use of artificial neural networks (ANN) in the power reserve control module enables the PV system to work at a specified power reserve ratio, producing appropriate power and mitigating frequency fluctuations in the microgrid. Additionally, a deep reinforcement learning (DRL) algorithm is employed as the decision maker for variable step-size control and initial power reserve ratio determination. Simulations were performed to validate the effectiveness of the proposed method, demonstrating a significant reduction in average frequency deviation by 72.36% when subjected to random variations in irradiance intensity and load conditions. Overall, the proposed AI-based power reserve control strategy has good potential for practical applications in real-world microgrids, promoting the absorption of new energy led by PV and reducing the phenomenon of light abandonment.

Coordinated Power Reserve Control of Wind Farm for Frequency Regulation

Coordinated Power Reserve Control of Wind Farm for Frequency Regulation

Flexible Active Power Control of Distributed Photovoltaic Systems With Integrated Battery Using Series Converter Configurations

Flexible active power control (FAPC) is becoming mandatory for PV systems, which is to limit/reserve the PV power below certain constraints as commanded, including the power ramp-rate control (PRRC), power limiting control (PLC), and power reserve control (PRC). In practice, energy storage (ES) such as batteries can be adopted to reduce the PV energy discarding in such cases. On the other hand, concerning the system overall cost, single-stage series power converter configurations are becoming attractive. Such configurations bring more flexibilities by integrating PV systems and batteries. However, the implementation of FAPC functions in series power converter configurations has not been systematically investigated. To fill this gap, the PRRC, PLC, and PRC strategies for series-PV-battery systems are developed in this article. With the proposed strategies, the power ramp-rate/limiting/reserve constraints are maintained by the coordinated control of individual converters. The reserved power is then distributed among all converters depending on the available power of individual PV converters, battery power, and state-of-charge (SoC) conditions. Experimental tests performed on a 1.6-kW system have validated the effectiveness of the proposed solution.

Power reserve control strategy of PV system for active power reserve under dynamic shading patterns

The de-loading technique in photovoltaics is used to reserve some active power for frequency regulation purposes. However, the selection of the de-loading method depends upon the shading conditions of photovoltaics. Many de-loading methods have already been developed for uniform shading conditions. Whereas for partial shading conditions, few methods are available for static shading patterns, while, the area of dynamic shading is untouched. Under dynamic shading, the global maximum power point changes continuously. Therefore, in this paper, in order to develop a power reserve under dynamic shading patterns of partial shading conditions, a trained artificial neural network is used. The information about the local and global maximum points is obtained from this neural network, whereas, the system de-loading is achieved using a de-loading algorithm. The neural network is trained using different irradiance patterns which lead to two or three peaks on the power vs. voltage curve of photovoltaics. The control is easy to implement and can handle up to three peak system. The simulation and experimental results have been used to verify the effectiveness of the control.

Flexible Power Point Tracking Using a Neural Network for Power Reserve Control in a Grid-Connected PV System

Renewable energy penetration in the global energy sector is in a state of steady growth. A major criterion imposed by the regulatory boards in the wake of electronic-driven power systems is frequency regulation capability. As more rooftop PV systems are under installation, the inertia response of the power utility system is descending. The PV systems are not equipped inherently with inertial or governor control for unseen frequency deviation scenarios. In the proposed method, inertial and droop frequency control is implemented by creating the necessary power reserve by the derated operation of the PV system. While, traditionally, PV systems operate in normal MPPT mode, a derated PV system follows a flexible power point tracking (FPPT) algorithm for creating virtual energy storage. The point of operation for the FPPT of the PV is determined by using a neural network block set available in MATLAB. For the verification of the controller, it is applied to a PV array in a modified IEEE-13 bus system modeled in the MATLAB/Simulink platform. The simulation results prove that when the proposed control is applied to the test network with renewable energy penetration, there is an improved system inertia response.

Frequency regulation in adaptive virtual inertia and power reserve control with high PV penetration by probabilistic forecasting

The large-scale deployment of sustainable energy sources has become a mandatory goal to reduce pollution from electricity production. As photovoltaic (PV) plants replace conventional synchronous generators (SGs), their significant inherent rotational inertia characteristics are reduced. The high penetration of PV results in reduced system inertia, leading to system frequency instability. Virtual inertial control (VIC) technology has attracted increasing interest because of its ability to mimic inertia. Adoption of the energy storage system (ESS) is hindered by the high cost, although it can be used to provide virtual inertia. The determined forecast gives PVs the ability to reserve power before shading and compensate the power when a system power drop occurs, which can increase system inertia. Nevertheless, it has forecast errors and energy waste in a stable state. To improve the stability of the microgrid and improve the ESS efficiency, this study proposes an adaptive forecasting-based (AFB) VIC method using probabilistic forecasts. The adaptive power reserve and virtual inertia control are proposed to reduce energy waste and increase system inertia. The simulation results reveal that the proposed method has adaptive system inertia to reduce the reserved power, required ESS power capacity, and battery aging.

Frequency Stability Analysis of a Low Inertia Power System with Interactions among Power Electronics Interfaced Generators with Frequency Response Capabilities

One of the main actions required to face and limit global warming is the substitution of conventional fossil-fueled electrical generators with renewable ones. Thus, it becomes fundamental to create non-dispatchable renewable generators able to provide services for power system stabilization that nowadays are delivered by conventional ones. Particularly, renewable generators are usually connected to the electrical power system through power electronic converters lacking natural responses to frequency variations. This challenges conventional frequency control methods that are based on synchronous generators’ capabilities, particularly in systems with high levels of non-synchronous generation. Solutions based on advanced controls that allow renewable generators to participate in frequency control are the subject of current research efforts worldwide. This paper contributes to these efforts by studying the benefits of introducing Power Reserve Control in photovoltaic generators and Extended Optimal Power Point Tracking control in wind generators to provide frequency control in low inertia power systems and the interactions between them. The tests and the simulations, prove that these kinds of controls help in stabilizing the system frequency thanks to the cooperative action of both types of renewable generators.

Frequency and Inertia Response Effects, Capabilities, and Possibilities in Renewable Energy Sources

Background & Objectives: The global power system is in a state of continuous evolution, incorporating more and more renewable energy systems. The converter-based systems are void of inherent inertia control behavior and are unable to curb minor frequency deviations. The traditional power system, on the other hand, is made up majorly of synchronous generators that have their inertia and governor response for frequency control. For improved inertial and primary frequency response, the existing frequency control methods need to be modified and an additional power reserve is to be maintained mandatorily for this purpose. Energy self-sufficient renewable distributed generator systems can be made possible through optimum active power control techniques. Also, when major global blackouts were analyzed for causes, solutions, and precautions, load shedding techniques were found to be a useful tool to prevent frequency collapse due to power imbalances. The pre-existing load shedding techniques were designed for traditional power systems and were tuned to eliminate low inertia generators as the first step to system stability restoration. To incorporate emerging energy possibilities, the changes in the mixed power system must be addressed and new frequency control capabilities of these systems must be researched. Discussion: In this paper, the power reserve control schemes that enable frequency regulation in the widely incorporated solar photovoltaic and wind turbine generating systems are discussed. Techniques for Under Frequency Load Shedding (UFLS) that can be effectively implemented in renewable energy enabled micro-grid environment for frequency regulation are also briefly discussed. The paper intends to study frequency control schemes and technologies that promote the development of self- sustaining micro-grids. Conclusion: The area of renewable energy research is fast emerging with immense scope for future developments. The comprehensive literature study confirms the possibilities of frequency and inertia response enhancement through optimum energy conservation and control of distributed energy systems.