The cost of connecting remote rural villages in China to the main power grid can be high due to geographical and population constraints. In such cases, it could be more economical to establish community microgrids, and tap into the local renewable resources. This paper studies the feasibility of operating islanded microgrids for rural villages. Three Chinese villages were selected, and simulation models were constructed to model their electrical consumption patterns. Subsequently, a multi-objective optimal dispatching model is proposed to minimize the operating costs as well as any associated environmental impacts. Numerical findings conducted in MATLAB show that community microgrid is a feasible option for rural electrification in China.
The integration small scale solar photovoltaic (PV) system existing utility grid is always a challenging task because of low in voltage level at DC bus. So that improve the level of voltage and easy transportation of electrical power three-port switched inductor based double boost DC-DC converter fed single-phase micro-inverter is introduced. The proposed converter system not only improves the DC voltage level to a desired one but also strengthen the synchronization with utility grid. Moreover, the proposed topology also reduces the overall cost and minimizes the switching losses. The design consideration of proposed converter topology and its various operating modes are presented in this study. Furthermore, the proposed 3-port switched inductor based dual DC-DC boost converter topology tied with micro-inverter and PV system is tested using MATLAB/Simulink software. Various simulation outputs and different investigation of the proposed structure defines the efficacy of the presented work.
Power system state estimation is an essential tool for monitoring the operating conditions of the grid. However, the collected measurements may not always be reliable due to bad data from various faults as well as the increasing potential of being exposed to cyber-attacks, particularly from data injection attacks. To enhance the accuracy of state estimation, this paper presents a back-propagation neural network to detect and identify bad data and false data injections. A variety of training data exhibiting different statistical properties were used for training. The developed strategy was tested on the IEEE 30-bus and 118-bus power systems using MATLAB. Simulation results revealed the feasibility of the method for the detection and differentiation of bad data and false data injections in various operating scenarios.
This paper analyzes the stability of a two-layer control strategy consisting of a primary droop control and a secondary consensus control for both DC and AC microgrids. Sensitivity analysis was carried out in time domain to determine the impact of various controller gains on the grid stability, particularly the power sharing capabilities of grid-forming inverters. Numerical assessments were conducted using a three-inverter grid in MATLAB. The stability performance of the DC microgrid is found to be more superior than its AC counterpart when subjected to controller perturbations.
The quality of measurement data directly determines the accuracy of the state estimation. In practice, erroneous measurement may exist due to various physical factors, and they are known as bad data. Moreover, the measured data may also be attacked by hackers. The existence of bad data and cyber attacks could cause the state estimation unable to estimate the actual system states. Therefore, it is of great significance to detect and differentiate bad data and cyber attacks in power system state estimation. To this end, a support vector machine was proposed in this paper. It was validated using IEEE 118 bus and IEEE 30 bus systems. Numerical results prove the effectiveness of the proposed method in identifying bad data and false data injection data.
This paper touches on three key areas of full electronic DC grid systems, in particular Medium Voltage DC (MVDC) grids, and presents advances at optimized DC grid planning, control stability, and efficient power converters. A solution of the specific mathematical optimization problem of DC grids allows targeted optimization while considering their unique flexibility. An advanced control approach demonstrates voltage stability, independent of grid configuration. A robust soft-switching extension to the DAB converter extends high-efficient operation to the full operation area.
Under the influence of mechanical characteristics such as pitch angle control, speed control and electrical characteristics such as electrical distance and state vector, the operation status of each unit in wind farm are different, therefore it is important to establish a suitable wind farm equivalent model. The author proposes the wind farm equivalent modeling method based on DBSCAN to solve the problem of outliers in equivalent clustering of wind turbine according to the wind farm measured operating data which are in transient and steady state and constracted from the wind turbine speed vector. The DIgSILENT / PowerFactory platform is employed to simulate the electromechanical transient of the wind farm and compared with the traditional stand-alone model and the detailed model. The simulation results show that the equivalent model of wind farm based on DBSCAN is close to the detailed model, which can accurately reflect the dynamic response characteristics of wind farm.
The increase of short-circuit fault capacity and fault ride-through (FRT) are the main issues of doubly fed induction generator (DFIG) based wind farm. In this paper, a new method of using saturated core fault current limiter (SCFCL) to improve FRT capability of DFIG-based wind farm is proposed. During fault condition in the grid, SCFCL not only limits the fault current but also contributes to maintain the stability of the generator terminal voltage and decrease the peak value of DC-link overvoltage at the instant of fault occurring. Accuracy and capability of the proposed method are confirmed by simulating a sample power system in MATLAB/Simulink software. Moreover, enhancement of different SCFCL impedance values and different installation locations are compared.
In this paper a simplified zero-sequence model of a medium-voltage network with three-core cables is proposed. The model is then used to analyze the distribution of earth currents in the network when a phase-to-ground fault occurs in the line between consumer substations. Then this paper studies how this distribution changes when the resistance of earth grids of consumer substations change and when fault location changes. Result shows that a large proportion of earth current flows back to the earth grid of source substation through sheaths and armors of cables instead of flowing to the earth grid of the nearest consumer substation. And this proportion is hardly affected by the resistance of earth grids of consumer substations or by fault location. The theoretical result is testified by simulation using PSCAD.
With the development of smart demand response (DR) technology, it provide new ideas to utilize DR technologies to participate in spinning reserve of power system. Based on smart DR technologies, this paper presents a dispatching framework with DR participating in power system's reserve in various time scales, and then a coordinated optimization model is proposed to determine how much capacity the DR should provide with considering of the cost of reserve. In this optimization model, the system cost includes both deterministic cost and risk cost, and the optimal total cost of DR participating in spinning reserve is the goal of the proposed coordinating optimization scheme. Finally, the feasibility and effectiveness of the proposed scheme is verified by numerical cases and simulation results.
Due to the effect of line impedance and unequal load distribution, reactive power supplied by distributed power resources (DR) based on voltage source converter could not be shared according to their droop gains and the power quality will also be affected in ac microgrid. In this paper, a novel hierarchical control of ac micro-grid according to different time scales is proposed to improve power Sharing and power Quality. In short time scale, larger droop gains is adopted to improve power sharing. In larger time scale, the no load frequency and voltage set points of droop characteristics are adjusted, improving the voltage and frequency quality. The proposed hierarchical control can both limit the reactive power sharing errors and improve the power quality, which can be applied in complex microgrid configurations. Finally, the performance of the proposed control strategy is verified by digital time-domain simulation in PSCAD/EMTDC software.
In recent years, rapid growth of the wind power all around the world highlights the requirement of developing accurate wind power forecasting method. Since the wind power generation mainly relies on wind speed and wind turbine condition, a novel wind power forecasting strategy considering wind turbine condition is proposed in this paper. The proposed strategy which can predict several-hours-ahead wind power is based on wavelet method and Support Vector Machine method. Real-world dataset is adopted to evaluate the efficiency of the proposed method. Simulation results show that the proposed method can improve wind power forecasting accuracy compared with traditional forecasting strategy.
Aiming at the two-core symmetric discrete thyristor controlled phase shifting transformer (TCSD-TCPST), its modeling and control strategies are studied in this paper. Firstly, the mathematical model of TCSD-TCPST considering its equivalent impedance is deduced. And the relationship among phase-shifting angle, tap position and equivalent impedance are derived. Then, two control strategies of TCSD-TCPST with different control objectives, phase shifting angle and active power, are proposed. Finally, Simulation results based on PSCAD/EMTDC show that the mathematical model can accurately reflect the steady-state characteristic of TCSD-TCPST on different tap positions and TCSD-TCPST can both quickly response to changes of control objectives when adopting two different control strategies.
Condition based maintenance and diagnosis technology plays an important role in power system reliability, because it is able to identify the faulty section in power system before the faults occur. With the technology development of smart grid which requires a more reliable power supply, a lot of researches have been focused on the transformer fault recognition. Based on this present situation, this paper introduces transformer fault recognition research status, and puts the current methods. Through the analysis of weakness of these current methods and the advantage of EDA-ANN method, a new method for the transformer fault recognition is designed to realize the fault recognition with dissolved gas. And through some real fault data, this proposed method is proven to be feasible and accurate.
A typical microgrid (MG) is composed of renewable energy generation systems including distributed energy resources (i.e., wind, photovoltaic etc.), energy storages and local loads. This paper gives a review on recent significant research initiatives carried out regarding energy management optimization of the MG. The idea is to present the basic architecture and regulation techniques of MG, including the forecasting methods of wind and solar generation, different energy storage technologies, the approaches of user management and integrated scheduling methods of the MG. In addition, an applicable scheduling method for MG that will integrate advanced techniques is introduced in this paper.
A new solution to eliminate inter-area low frequency oscillation through accurate control of absolute generator rotor angles is put forward recently. The new solution can achieve no deviating regulation of frequency and absolute rotor angles. As a result, low frequency oscillations can be eliminated. This paper presents the state matrix for a single-machine infinite bus system and a two machine system when the angle controller is applied. Analysis shows that both local and inter area oscillations exist in the two machine system. Increasing the proportional coefficient will decrease the damping ratio for these oscillations, while increasing the differential coefficient will increase the damping ratio. Besides, integration time in the new governor must be big enough, otherwise the system may become unstable. Simulation also shows that, the proportional coefficient should be set to a value as high as possible. This way, angle controller will be more effective, since angle swing caused by disturbance will be restricted to the local area.
In developing countries, a large growth in power demand necessitates the efficient distribution of available power. Whenever power demand is more than the power generation load shedding is carried out. Under the current scheme, load shedding is done by disconnecting an entire feeder, employing ‘Round robin’ technique. In most cases, this method fails to shed exact amount of load resulting in either over-shedding or under-shedding. Further, load shedding is done regardless of the type of the load connected to a feeder. This Paper proposes a novel grading scheme for loads to minimize the impact of load shedding by taking revenue loss and social factors into consideration. The genetic algorithm developed minimizes the error between the amount of load to be shed and the actual load shed, simultaneously optimizing the overall impact of load shedding. The algorithm is developed for a smart grid environment, assuming a two way communication between the consumer and the utility is present. The algorithm is tested on a sample system comprising practical feeder data.
One of the main objectives of Smart grid is to provide service that is reliable, secure and efficient. As a part of smart grid it is very essential to evaluate each and every element separately in the grid level to ensure reliable operation of the grid. In this paper, distribution transformer (DTR) requirements for smart grid have been considered. Distribution transformer is one of the most important elements of electrical distribution network. For smart grid to operate efficiently there is a need for smartening the transformers, which are the hub for collection and distribution of energy. As part of the distribution network, there are millions of distribution transformers in the national network that do not have any monitoring and communication capabilities. Smartening the transformers will require development and deployment of wide range of technologies. This paper attempts to present the features needed in distribution transformers to realize a smarter grid. Required technologies to transform the present day distribution transformers to smart transformers are discussed. Analysis has been carried out on the performance requirements and evaluation of distribution transformers when they are integrated to grid level. Some applications of wireless sensors and communication to enhance condition monitoring and maintenance practices in the distribution grid are recommended. The paper also studies compliance needed to the existing standards such as IEC 60076-7 [3].
Power System security has become a major concern across the global power system community. This paper presents wide area measurement system (WAMS) based security assessment and monitoring of modern power system. A new three dimensional security index (TDSI) has been proposed for online security monitoring of modern power system with large scale renewable energy penetration. Phasor measurement unit (PMU) based WAMS has been implemented in western Danish Power System to realize online security monitoring and assessment in power system control center. The proposed security monitoring system has been demonstrated in DigSILENT PowerFactory environment.
In future smart grids, smart metering, active distribution network management, electric-mobility and a high penetration of distributed generation are anticipated. At times of high PV production and low electricity demand, network voltage rise may exceed limits resulting in a consequent curtailment of PV generation reducing the energy yield. A decrease in energy yield reduces the PV system economic viability which may result in the rate of PV adoption being less than anticipated depending upon how curtailment is handled. The potential of smart grids, especially by means of Demand Side Management (DSM), to facilitate PV penetration by capturing maximum PV energy is investigated in this paper. The impact of varying PV penetrations on the node voltages of a generic UK urban distribution network is analyzed by means of simplified distribution load flow to identify voltage limit violations and PV generation hosting capacity of the network. Then the feasibility of maximizing PV energy capture by time shifting flexible consumer loads is investigated. It is seen that the entire PV over-production in the LV feeder can be captured by the use of flexible wet loads and electric water heating alone, for up to 90 % PV penetration in the MV network, beyond which additional measures were found necessary.
