Battery storage configuration for multi-energy microgrid considering primary frequency regulation and demand response

Estimating the system efficiency of the multifunctional hydrogen complex at nuclear power plants

In order to meet the quality requirement of primary frequency regulation and AGC (Automatic Generation Control) for power plants in China Southern Power Grid "two rules", the paper designs a AGC and primary frequency regulation monitoring and management system for power plant by analyzing the system requirements and combining with the actual situation of the power plant. Based on data acquisition and processing module and real-time database, the system has realized many functions such as automatic collecting, calculating and dealing with the data of the AGC and primary frequency regulation, giving a warning and analyzing the reason when the AGC and primary frequency regulation service are disqualification. After a period of trial running, it shows that the monitoring and management system can improve the quality of the AGC and primary frequency regulation services provided by the power plant. At the same time, the system can also provide guarantee for the safety, stability and economy of the generators.

The power system frequency stability problem has been the focus of attention since 1920s. Primary frequency regulation (PFR) is one of vital methods to maintain frequency stability, especially when the power system suffers a sudden load disturbance, such as the substation tripping or generator outage accident. To a power system, the more power units participating in PFR, the frequency stability will be controlled better. With the rapid development of nuclear power units in China, the study of the nuclear power units participating in PFR of power system has becoming a pressing problem. In the present study, a detailed nonlinear dynamic mathematical model of the whole pressurized water reactor (PWR) nuclear power plant is built. The dynamic calculation codes are compiled to dynamic link library (DLL) files, which are developed by using FORTRAN language, and the compiled DLL files are embedded into MATLAB/SIMULINK simulation platform by using S-function, the control systems are designed and the whole system of PWR nuclear power plant is simulated in MATLAB/SIMULINK finally. In this method, the operation and control mode of PWR participating in PFR of power system is analyzed and simulated. The simulations results show that the PWR nuclear units are feasible in participating in PFR from safety and economy.

This study focuses on the participation of energy storage in primary frequency regulation of offshore wind farms. A frequency regulation performance evaluation indicator is designed, and the black-start capability of the wind farm after shutdown is also considered. By equivalently processing the black-start time, a black-start capability evaluation indicator is designed. An energy storage strategy is adopted to balance power charging and discharging during the primary frequency regulation cycle. Considering the service life of energy storage batteries and the maximum number of charge/discharge cycles, a multi-objective comprehensive optimization model is proposed, which integrates frequency regulation performance, annual average investment cost of energy storage, black-start capability, and wind energy utilization rate. The designed model is solved using a genetic algorithm. Finally, a case study of an offshore wind farm is given to compare and analyze the primary frequency regulation with energy storage participation and the joint frequency regulation of wind and energy storage, which verifies the effectiveness of the proposed designed model and algorithm.

A dynamic demand response control strategy for isolated microgrid with primary frequency regulation

Due to a large number of grid-connected wind turbines don't have the ability to respond to system frequency changes, problems on frequency stability of power system have become increasingly prominent. At present, the primary frequency regulation of wind turbines is mostly based on the method of additional frequency regulation control to change the reference value of electromagnetic power, so as to realize that wind turbines can participate in the system frequency regulation. However, the method of additional frequency regulation control does not t consider the conflict of power increment between the power tracking controller and the frequency regulation controller, which lead to the power increment required for the primary frequency regulation can't reach the target value. Based on this issue, the paper combines the original power tracking technology of wind turbines with the existing frequency regulation technology, and change the signal of frequency deviation by the power tracking curve of the wind turbine, which realize the inertial response and primary frequency regulation of the unit through the fast active power control of the wind turbine. That the purpose of frequency regulation is realized and the power tracking curve is changed, by converting the active output required for the frequency regulation control into the increment load reduction. The simulation results show that, based on the control method in the paper, the double-fed wind turbine can fully achieve the target increment needed for primary frequency regulation, which makes the wind turbines more reliable and effective to participate in system of frequency regulation.

This paper integrates the wind turbines (WTs) into the interconnected power system and designs a distributed model predictive control (DMPC) controller for the primary frequency regulation problem. The WTs have been treated as a part of the power system to take part in primary frequency regulation with load disturbances. A frequency response model of multi-area power system including WTs is introduced, in which the physical constraints of the governors and turbines are considered. The distributed model predictive controller is designed by posing the primary frequency regulation problem as disturbance rejection problem of large system with state and input constraints. Analysis and simulation results for a two-area interconnected power system with WTs show possible improvements on closed-loop performance, while respecting physical hard constraints. Comparisons have been made made between the DMPC controller with and without WTs. The results confirm the superiority of the proposed DMPC scheme with the participation of the wind turbines in the primary frequency regulation.

Bi-level non-convex joint optimization model of energy storage in energy and primary frequency regulation markets

In order to further improve the performance of primary frequency modulation (PFM) by battery energy storage, a new control strategy is proposed. By analysing the characteristics of virtual inertia response and virtual droop control, the artificial dead zone of energy storage participating in frequency modulation is set based on virtual inertial control to make it respond quickly and improve the characteristics of energy storage to suppress frequency deviation change rate; In this paper, the remaining energy and load disturbance of the energy storage battery are taken as the double inputs, and the fuzzy control strategy is used to derive the function relationship between the virtual droop coefficient and the two inputs to ensure that the charging and discharging power of the energy storage battery is suitable for the actual needs. The load change rate is used to predict the load change at the next moment. Based on this, the coefficients of virtual inertia control and virtual droop control are determined, and the output coefficients of both are optimized to achieve the optimal frequency regulation effect. Three evaluation indexes are proposed to evaluate the control strategy in this paper. Finally, the simulation model is established in MATLAB/Simulink and the case study is carried out in a regional power grid. The proposed strategy can effectively improve the primary frequency regulation of power grid and has positive significance for maintaining energy storage battery.

Among the ancillary services, a great number of cost allocation strategies have been broadly developed in the deregulated environment. Generally, the utilization of such services can be determined by directly evaluating the actual amount of the usage or by indirectly analyzing the fair/reasonable contribution/attribution to the market participants. In the case of the primary frequency regulation (PFR) service, which is operated by the participating generating units to maintain the real-time balance between the generation and load, the discussion of the PFR service attributed to the load side has still received relatively little attention. In this paper, a new strategy of the cost allocation of the PFR service from the customer side is proposed. Two main factors, the load fluctuation and the frequent demand change, are considered to figure out the PFR reaction relating to the different substations. The design of a scheme for determining the cost allocation index of the PFR service can be applied to the presently exiting power market. In addition, the actually load series recorded from the extra-high voltage (EHV) substations of the Taipower system located in northern, central, and southern Taiwan are meticulously analyzed and utilized to verify the feasibility and practicability of cost allocation.

This paper presents the analysis of the impact of frequency droop control on the primary frequency regulation (PFR) with the use of battery energy storage system BESS in insolated systems. The presented analysis is based on the characteristic the output power and frequency of the batteries that is used in this type of control. The analysis of behavior of frequency in insolated systems is an aspect that must be considered for a correct adjustment of the operation of the BESS in the PFR and its lifetime. The performance results show that not is necessary a small dead band in the characteristic output power and frequency of batteries for have a good response in the PFR and this protects the life of the batteries. The variations in the dead band of the characteristic only has impact on the first transient of the frequency while with a wide dead band and a small droop (R) is possible obtained a good control and to protect the lifetime of the BESS.

As the amount of distributed energy storage (DES) in a power system continues to increase, it will not be long before there are multiple DES aggregators participating in frequency regulation, and the realization of their coordinated control is a critical topic of current research. This study focused on the primary frequency regulation (PFR) power allocation strategy among multiple DES aggregators participating in PFR. This study first calculated the PFR demand according to a system frequency response model of the power system with DESs. Next, a PFR power allocation model of DES aggregators was developed based on model predictive control. The objective of this model was to minimize the overall frequency regulation cost while satisfying all of the constraints of DESs. Finally, the distributed interior point method was used to solve the model rapidly. The correctness and effectiveness of the proposed model and algorithm were verified on two unified transmission and distribution systems with DES aggregators used to supply the PFR service. The results revealed that the proposed model could effectively allocate PFR power to the various types of energy storage, with the additional benefits of slowing down the shift in the state of charge for energy storage units and ensuring the continuity of energy storage participation in frequency regulation.

With the penetration of wind power increasing continuously, the inertia and the capability of primary frequency regulation of grid are declining. To deal with this problem effectively, additional primary frequency regulation control and inertia control adopted in wind turbines are necessary. However, at present, the functional orientation of primary frequency regulation control and inertia control is still unclear. It is urgent to clarify the difference between the two kinds of control methods and to make clear the demand of power grid for them. In this paper, based on analysis of main methods of primary frequency regulation and inertia control of doubly-fed induction generators (DFIG), the functional orientation distinction between inertia support function and primary frequency regulation function is studied from perspective of control principles and control results. The different effectiveness of different control functions on the frequency regulation process in different scenarios are analyzed by simulations.

There are a lot of nonlinear loads in real low voltage microgrid system. It will cause serious output voltage and grid current harmonic distortions problems in island and grid-connected modes, respectively. To solve this problem, this paper proposes a droop control scheme with quasi-proportion and resonant (quasi-PR) controller based on αβ stationary reference frame to make microgrid smoothly switch between grid-connected and island modes without changing control method. Moreover, in island mode, not only stable output voltage and frequency, but also reduced output voltage harmonics with added nonlinear loads can be achieved; In grid-connected mode, not only constant power, but also reduced grid current harmonics can be achieved. Simulation results verify the effectiveness of the proposed control scheme.

As the proportion of new energy generation rises, its capacity for primary frequency regulation needs to be emphasized. To analyze the primary frequency regulation capability of new energy power resources, this paper proposes to use the index sensitivity method to analyze the primary frequency regulation parameters. The IEEE 39-bus system with new energy generation was built based on PSD-BPA software and its parameter settings were analyzed in correspondence with the technical requirements. To calculate the Index sensitivity of different frequency regulation parameters to the system frequency, two perturbations are set. Finally, a comparison of the Index sensitivity of PV stations and wind farms reveals differences in their support capabilities.