Stable Operation Of Microgrid Research Articles

Multi-objective planning and optimization of microgrid lithium iron phosphate battery energy storage system consider power supply status and CCER transactions

Lithium iron phosphate battery (LIPB) is the key equipment of battery energy storage system (BESS), which plays a major role in promoting the economic and stable operation of microgrid. Based on the advancement of LIPB technology and efficient consumption of renewable energy, two power supply planning strategies and the china certified emission reduction (CCER) model are proposed respectively. Based on it, the multi-objective planning optimization model with economic benefits, environmental benefits and power supply stability as the objective function is established for the first time, and the Newton Weighted Sum Frisch method (NWSFA) solution model is adopted. In the planning process, rain flow counting method is used to research the life of BESS, which improves the accuracy of energy storage annual cost calculation. A park in northern China is taken as a case study to demonstrate the application of this model. The simulation results show that the annual economic operating cost of BESS is decreased by 18.81%, the energy supply reliability is increased by 0.15%, and the optimal electricity price adjustment ratio of the system is 15%.

An efficient DLN2-CRSO approach based dynamic stability enhancement in micro-grid system

An efficient regulation of the frequency and voltage of operation of the microgrid in island mode is essential; otherwise, the voltage and frequency deviations in the microgrid will increase the energy imbalance by going beyond the tolerance range. In this manuscript, an efficient hybrid approach to improve the dynamic stability of the micro grid (MG) is proposed. The proposed hybrid approach is the combined performance of Deep learning neural network (DLNN) and chaotic rat swarm optimizer (CRSO), hence it is named as DLN2-CRSO. To improve the searching ability and speed of the convergence, RSO is improved by the chaotic version of RSO. The proposed DLN2-CRSO approach is utilized the low-signal stability analysis under the entire operating points. The major objective of the proposed approach is the stability enhancement. To improve the dynamic stability through the integration of multiple distributed generation units in the micro grid, deep planning neural network is used. The control parameters of the DPNNs are identified by the chaotic rat swarm optimizer (CRSO) approach. The proposed approach reduces the reactive power mismatches among the converters and guarantees the stable operation of MG. The performance of proposed approach is authenticated with simulation outcomes, which is performed with MATLAB/Simulink platform. The performance of the proposed technique is evaluated with statistical measures like mean, median and standard deviation with existing methods. Also the efficiency of the proposed technique reaches 95.6346%.

Simulation and analysis of sag control of microgrid inverters

A good inverter control strategy helps to maintain the stable operation of microgrid, and sag control is a common control strategy. Since the traditional sag control has the problem of difficult to stabilize the voltage frequency when switching the load. In this paper, we propose an improved sag control by introducing fuzzy control and linear self-rejecting control techniques into the voltage and current dual-loop structure of sag control, respectively, and build the simulation in Matlab/Simulink. The simulation comparison results show that the linear self-rejecting control has the best performance in stabilizing the voltage and frequency and tracking the reference value during load switching of the microgrid with better robustness than the PI control in the traditional sag control and the improved fuzzy control.

Optimal modeling and analysis of microgrid lithium iron phosphate battery energy storage system under different power supply states

Lithium iron phosphate battery (LIPB) is the key equipment of battery energy storage system (BESS), which plays a major role in promoting the economic and stable operation of microgrid. Based on the advancement of LIPB technology, two power supply operation strategies for BESS are proposed. One is the normal power supply, and the other is emergency power supply. Under the two operation strategies, the multi-objective optimization model with economic benefits, environmental benefits and power supply stability as the objective function is established for the first time, and the Newton Weighted Sum Frisch method (NWSFA) solution model is adopted. In the operation process, rain flow counting method is used for service life research of BESS, which improves the accuracy of energy storage annual cost calculation. A park in northern China is taken as a case study to demonstrate the application of this model. The simulation results show that the annual economic operating cost of BESS decreases by 19.12%, the energy supply reliability increases by 0.15%, and the optimal power price adjustment ratio of the system is 15%.

Power coordination control strategy of microgrid based on photovoltaic generation

In order to solve the large-scale grid-connected photovoltaic cells caused by power fluctuations, power quality decline and other issues. This paper proposes and researches a power coordination control strategy for microgrid based on photovoltaic power generation. The principle of photovoltaic cells and the switching of maximum power point tracking and limited power mode are studied. The stability control methods of DC bus voltage, AC bus wire and frequency are studied. The model of microgrid is established and moreover, based on the power of microgrid and the charging state of storage battery, the operation of microgrid is divided into different working modes. The stable operation of microgrid is realized by adjusting the output power of each unit in different working modes. The calculation shows that the control strategy can effectively reduce the power fluctuation in the microgrid and improve the output power of renewable energy. Finally, the feasibility and effectiveness of the proposed methods are verified by experiments.

Fixed Frequency Slide Mode Controller Cascaded with Proportional Resonant Controller and Droop Controller a New Approach for an Effective 3-Phase Microgrid under Islanded Operation

Inverter-based distributed generation (DG) units in microgrid (MG) call for robust and precise control methods that attain high performance under both normal and unbalanced conditions. Efficient control scheme needs to be investigated for the proper operation of a microgrid in both grid-tied and islanding condition. Using the excellent performance of slide mode controller(SMC) for nonlinear loads and the ability of proportional resonant(PR) controller to precisely track reference sinusoidal signal, a cascaded SMC and PR controller has been proposed for stable operation of microgrid. The phenomenon of chattering a drawback in SMC is eliminated by using fixed frequency switching of the inverter circuit using smooth control law in a narrow boundary layer. For effective sharing of the loads among different DER’s during isolation mode of operation a droop controller is proposed. The proposed controller showed excellent results for linear and nonlinear loading. To analyze the performance of droop controller, proposed for parallel operation of two DG units, simulations are performed under linear and distorted load conditions. Results obtained shows that proposed cascaded controller and droop controller improves the output by the reduction of the total harmonic distortion (THD), high degree of robustness, fast response time, and efficient power sharing among DG units.

Multi-objective optimal scheduling of a microgrid with uncertainties of renewable power generation considering user satisfaction

The Microgrid (MG) system combines different types of distributed generation units. It realizes the complementary of multiple energy sources, thereby improving energy efficiency, and power supply reliability. However, it brings significant challenges to the stable operation of MG due to the randomness and uncertainty of renewable energy power generation. By modeling the uncertainty of renewable power generation with probabilistic constraints, a practical multi-objective optimal scheduling model of grid-connected MGs is proposed for minimizing the operating costs and improving the user experience based on chance-constrained programming (CCP). Besides, the sample average approximation (SAA) is applied to transform the model into a multi-objective mixed-integer linear programming (MILP) formulation. Then, the membership function is employed to obtain the optimal weights of the multi-objective problem. Furthermore, from the perspective of demand-side management, a user satisfaction indicator is introduced to evaluate the user experience when the economy and reliability of the MG system are guaranteed. The simulation results of a real world MG demonstrates the effectiveness of the proposed method.

A novel control strategy of the seamless transitions between grid-connected and islanding operation modes for the multiple complementary power microgrid

ABSTRACT Micro-grid needs to integrate islanding operation mode and grid-connected operation mode together. Smooth switching between islanding operation mode and grid-connected operation mode is the key to ensure stable operation of micro-grid. In order to solve the problem of transient electrical quantity mutation in the process of dual-mode switching in microgrid, a dual-mode combined seamless switching control strategy based on current tracking is proposed for the battery inverter of the main control unit in this paper, to make the reference current of the input current inner loop controller can follow the current state at the moment before the switching moment, and maintain the correct initial value, so that the microgrid can switch smoothly and stably between grid-connected state and islanding state. Simulation results are provided to verify the effectiveness of proposed control strategy, by Power Systems Computer-Aided Design/Electro Magnetic Transient in DC System (PSCAD/EMTDC) simulation software.

Operation characteristics and key technology analysis of high-penetration renewable energy microgrid

With the increasing penetration rate, the strong intermittency and volatility of renewable energy, and the large-scale use of power electronic devices, the safe and stable operation of microgrids has been seriously affected. This paper analyzed the impact of high-penetration renewable energy on power system flow distribution, power quality, operating status, relay protection, etc. And specifically studied several specific keys to improve the operating stability of the microgrid including high-penetration renewable energy.

Frequency Regulation of an Isolated Microgrid With Electric Vehicles and Energy Storage System Integration Using Adaptive and Model Predictive Controllers

Energy storage system (ESS) possesses tremendous potential to counter both the rapid growth of intermittent renewable energy resources (RESs) and provide frequency support to the microgrid (MG). Since the deployment of ESS has overcome the imbalance between generation and consumption, however, their massive cost, as well as degradation tendency, are the restricting considerations that demand alternative solutions to provide stable microgrid operation. To assist ESS, the electric vehicles (EVs) are incorporated into the system. EVs have been gradually commercially viable and considerable focus has been paid to vehicle-to-grid technologies. Appropriate collaboration between ESS and EVs has good capability to manage the frequency irregularities to ensure the efficient operation of the MG. This article presents a novel combination of two control techniques i.e., model predictive control (MPC) and adaptive droop control (ADC), to tackle the frequency regulation issue in the isolated MG, by effectively controlling the ESS and EVs during the large-scale integration of RESs or huge change in load demand. Firstly, the MPC regulates the ESS according to the system frequency deviation, and secondly, the ADC manages the power of EVs according to system specifications by retaining the least possible power for potential usage of EVs. Moreover, an advanced genetic algorithm is applied to tune the MPC and ADC parameters in order to achieve optimized performance. An isolated MG is modeled and verified in MATLAB/Simulink using the above-mentioned control techniques. Further, different case studies are taken into account to validate the combination of ADC and MPC for frequency regulation of an isolated MG. Additionally, the proposed MPC controller is compared with fuzzy logic proportional-integral (FPI) controller and proportional-integral (PI) controller, the MPC provides better performance results as compared with FPI and PI controllers.

Robust frequency control in a wind-diesel autonomous microgrid: A novel two-level control approach

Volatile nature in renewable power output, stochastic nature of load and continuous change in system structure are the key factors affecting the stable operation of microgrid (MG), particularly in frequency control. Appropriate control schemes are indispensable to reduce the frequency fluctuations in MG under such scenarios. Concerning to these issues; this paper proposes a novel two-level control mechanism approach to mitigate the frequency fluctuations in the wind-diesel standalone MG. In the first level, from wind turbine generator (WTG) side, a fixed wind power command is replaced by an optimum adaptive wind power command based on the power system operating conditions and wind speed conditions. To perform this task, the fuzzy logic approach (FLA) is employed by considering change in wind velocity and frequency deviation as inputs and change in WTG power as output. In the second level, a robust FLA tuned Proportional Integral (PI) controller is proposed to regulate the output power of the diesel engine generator (DEG) for the further reduction in MG frequency fluctuations. With this proposed two-level approach, the MG frequency fluctuations are within the limits in all possible operating conditions, which include some critical operating scenarios. Moreover, the superiority of proposed approach in dynamic performance enhancement against load and wind power changes is proven by comparing with various powerful controllers in the literature.

Fully distributed hierarchical control strategy for multi‐inverter‐based AC microgrids

A fully distributed hierarchical control strategy for multiple inverters-based AC microgrid is proposed. The developed controller provides real-time economic dispatch along with the network frequency and average voltage restoration. The controllers cooperate with neighbours using sparse communication network and perform local computations to achieve the assigned objectives. The economic dispatch control unit is embedded with the frequency restoration at the secondary level controller to change the active power supply from the inverter. The voltage controller along with reactive power controller ensures the proportional reactive power sharing as well as network average voltage regulation. The average voltage regulation aids the individual inverter to provide required reactive power demand, with a small, comprise at the terminal output voltages from the nominal values. The convergence of the proposed controller is proved using the Lyapunov stability criteria. The maximum allowable communication delay that obligate stable microgrid operation is derived. The simulation results verify the efficacy of the proposed controller. Experimental validation is also presented, and the controller ability to ride through communication failure and load perturbation condition is demonstrated.

Economic-environmental dispatch of microgrid based on improved quantum particle swarm optimization

As a practical choice to deal with energy security and low-carbon development, the microgrid can effectively promote the consumption of renewable energy. However, the volatility of renewable energy output affects the stable operation of microgrid. In order to ensure the reliability of power supply and improve the economy and environmental protection, this paper studied the short-term economic-environmental (EED) problem of the microgrid. Based on the dispatching model, this paper introduced the differential evolution (DE) into quantum particle swarm optimization (QPSO) and used the improved QPSO to solve problem. Through Friedman test, the performance is compared. The results show that: First, renewable energy should be preferred for generation, micro gas turbine take priority to meet thermal load, fuel cell, and storage battery are used for power supplement and power transaction. This plan can optimize the units output and reduce the emission of pollution gas on the premise of satisfying the regular operation of the microgrid. Second, in the later stage of improved QPSO, the ability to jump out of local optimal solution is stronger. Then, the improved QPSO can obtain better results. Therefore, the improved QPSO has better performance, and it is more suitable for solving microgrid EED problems than QPSO and CLQPSO.

Performance Analysis of a Dq Power Flow-Based Energy Storage Control System for Microgrid Applications

This paper presents a dq power flow based energy storage control system for reliable and stable operation of a renewable power generation based microgrid system. The control objectives are storing the excess energy from the microgrid into the storage unit or supplying energy deficit from the storage unit to the microgrid to achieve power equity between the generation and load, and regulation of voltage and frequency during stand-alone microgrid operation. Whereas during grid-connected microgrid operation, the control objective is to ensure storing energy in the storage unit and exchange power between the microgrid and the utility grid. The proposed controller is developed for inverter interface energy storages using dq power flow. The dq power flow is formulated using bus voltage components and the bus admittance matrix in dq frame. The dq power flow in the developed controller generates command (reference) active and reactive powers for the inverter interfaced storage unit connected to the microgrid buses. In addition, the implemented current controller of the inverter assures such command powers exchange between the storage unit and the microgrid. The developed dq power flow based storage unit (DQPFSU) control system is tested under various operating conditions for both in grid-connected and stand-alone microgrid operation. The test results of the developed DQPFSU controller illustrates satisfactory performance in generating fast control actions to ensure reliable and stable microgrid operation under various changing conditions. Moreover, the validity of such control actions has examined from the frequency response and bus voltages of the case study microgrid under various tested operational conditions.

Stability-Constrained Microgrid Operation Scheduling Incorporating Frequency Control Reserve

This paper presents a two-stage microgrid scheduling strategy in which the frequency control reserve (FCR) is incorporated to ensure economic, reliable, and stable microgrid operation in a joint energy and ancillary service market environment. In addition, to using such reserve to limit frequency excursions caused by uncertainties of active loads and renewable generation, this paper is focused on determining the optimal provision of reserve for microgrid operation mode switching to assure sufficient reserve is available and readily deployable at the disposal of the microgrid operator. The scheduling problem is formulated as a two-stage chance-constrained programming (CCP) model where the power balance chance constraints are used to determine the trade-off between operational economy and stability risk exposure. The chance-constrained formulation is then approximated as a deterministic mixed-integer linear programming (MILP) model for solution. Two sets of policy studies are performed through simulation to evaluate the effectiveness of the proposed strategy in enhancing the operational performance of a microgrid through optimal scheduling.

An Advance Modulation Technique for Single-Phase Voltage Source Inverter to Integrate SMES Into Low-Voltage Distribution

Nowadays, the grid-integrated superconducting magnetic energy storage (SMES) has received significant attention due to its short delay during charging and discharging processes for stable operation of microgrid. The energy conversion efficiency of the SMES mainly depends upon the switching algorithm of its power conditioning system. Traditional modulation techniques can cause considerable losses and poor conversion efficiency. In this paper, an advance pulsewidth modulation technique for an inverter to use with an SMES integrated with the single-phase low-voltage distribution grid is proposed, which provides a lower total harmonic distortion and reduces power conversion losses. The proposed technique improves the performance of the power conditioning system of SMES by reducing energy consumption from the SMES during short-circuit fault, voltage collapse, etc. The proposed algorithm is also verified in a laboratory test platform.

Distributed Optimal Energy Management for Microgrids in the Presence of Time-Varying Communication Delays

This paper investigates the issues of the distributed energy management problem (EMP) of Microgrids in the presence of communication delays. To address this issue, a consensus-based distributed algorithm is proposed to integrate the economic dispatch and demand response, which can optimally assign the energy among generation units and load units with the objective of maximizing the total social welfare of the power system. Different from existing energy management algorithms, a nonuniform time-varying delays model is considered and embedded into the design of our algorithm, such that each unit can achieve collaborative optimization without the requirement of fixed delays information, which has both theoretical merits and practical engineering value for the efficient and stable operation of Microgrids. Moreover, it is proved that the proposed algorithm can converge to the optimal solution under some sufficient conditions. Finally, the correctness and effectiveness of the proposed method are validated by several simulation results.

A Study on Hybrid DC Micro-Grid System

With the growing demand of electricity, deployment of microgrid is becoming an attractive option to meet the energy demands. At present, large-scale wind/solar hybrid system is of great potential for development. The large-scale wind/solar hybrid system is of higher reliability compared with wind power generation alone and solar power generation alone However, a grid connected microgrid suffers a crucial stability issues during a fault in utility grid. For stable operation of microgrid during fault in grid. In this paper transient stability of the microgrid is studied during fault in utility grid. This research work presents the design and implementation of a hybrid renewable energy system that allows a cost-efficient and sustainable energy supply of the loads. The integration of the solar system with the network is rather complex and expensive. With this construction proposal, however, it is not only possible to create an economical and simple hybrid system, but also a reliable, efficient and economical system.

$L_{1}$ Adaptive Droop Control for AC Microgrid With Small Mesh Network

The proposed paper is mainly focused on achieving stable operation of microgrid having reconfigurable architecture leading to huge variation in network parameters. The variation in network parameters may not be easily handled by conventional droop controllers, which are mainly designed while assuming fixed network configuration. However, these assumptions become invalid for a microgrid having small mesh network with reconfigurable structure. Therefore, it is most important for a microgrid to remain stable not only during various changes in droop characteristics but also during dynamic topological changes. The $L_1$ controllers are well known for their robustness under wide parametric variations. Therefore, a novel $L_{1}$ adaptive controller has been designed to achieve enhanced stability of microgrid under the varying network configuration and variable droop controller characteristics. The proposed method is simulated in MATLAB/ Simulink and verified on field programmable gate array (FPGA)-based real world hardware platform.

Frequency $H_{2}/H_{∞}$ optimizing control for isolated microgrid based on IPSO algorithm

Affected by the fluctuation of wind and load, large frequency change will occur in independently islanded wind-diesel complementary microgrid. In order to suppress disturbance and ensure the normal operation of microgrid, a $H_{2}/H_{∞}$ controller optimized by improved particle swarm algorithm is designed to control the frequency of microgrid. $H_{2}/H_{∞}$ hybrid control can well balance the robustness and the performance of system. Particle swarm algorithm is improved. Adaptive method is used to adjust the inertia weight, and cloud fuzzy deduction is used to determine the learning factor. Improved particle swarm algorithm can solve the problem of local extremum, so the global optimal goal can be achieved. It is used to optimize $H_{2}/H_{∞}$ controller, so as to overcome the conservative property of solution by linear matrix inequality and improve the adaptive ability of controller. Simulation results show that with a $H_{2}/H_{∞}$ controller optimized by improved particle swarm algorithm, the frequency fluctuations caused by the wind and load is decreased, and the safety and stable operation of microgrid is guaranteed.