Shun Tao

Coordinated EV charging and its application in distribution networks

Scale-of electric vehicle (EV) charging will bring great impacts to the operation of the power grid. Coordinated charging can guide these effects to the beneficial aspects. This paper firstly derived a steady mathematical model of single charge load as the basis of coordinated charging scheduling. Secondly, based on the schedulability of the EV charging load in time domain, a new kind of coordinated charging control method is put forward. An optimal model is proposed with the objective of minimum total load energy, concerning capacity of transformer and distributing lines and demands of charging time. By changing the charging time of each EV, minimum fluctuation of the total load curve be achieved. This method is verified the effectiveness by the simulation results. At last, the application design scheme in actual EV charging station is introduced for engineering application.

Analysis of sag vulearability area of a large power system based on information fusion of CIM

This paper proposes an information fusion method of Common Information Model(CIM) for analysis of sag vulnerability area, in order to automatically track the operation state of system. Multiplayer structure of information fusion containing data fusion, feature fusion and decision fusion, is built to obtain basic data required by analysis of sag vulnerability area like topologies, equipment parameters, the measured values of bus voltage, etc. Then the flow chart for calculating sag vulnerability area is given and fault position method based on interpolation is adopted. Finally, the method is applied to a large region grid and results show its possibility. Based on such a mode of sag vulnerability area analysis, it is also discussed for further application research.

Current Detection Method and its Application of an Extension pq Theory

In the modern society, with the rapid development of industrial technology and information industry, electrical loads become more and more complex. As a result, the harmonics and reactive power problems have become increasingly serious. In the non-sinusoidal conditions, conventional power definitions don’t work well any more. Power theory is one of the foundations of financial accounts for energy, evaluation of the efficiency of power transmission and control of current compensation. Among them, the instantaneous reactive power theory is regarded as one of the most promising power theories. What’s more, it has been improved. Based on the three-phase three-wire system and four kinds of different supply voltage conditions, this paper compares the instantaneous reactive power theory (pq theory) with the extension pq theory. At last, the simulation results are presented. As a conclusion, the extension pq theory is the improvement of the pq theory and has a wider applicability.

Monitoring and analysis of power quality in electric vehicle charging stations

Electric vehicle (EV) charging may lead to power quality problems for chargers work as electric-electronic converters. It is necessary to get to know the influence to the power system caused by chargers before EVs operating in scale. Based on monitoring data, power quality problems in EV charging stations are presented and analyzed in this paper. Harmonic current emissions of different kinds of chargers are investigated first. Then harmonic current saturation is detected and discussed. In the next section, power quality of bus voltage and the influencing factors are analyzed . At the end of this paper, suggestions and recommendations are given to improve the power quality of EV charging stations.

Power Demand of Electric Bus Charging Station Modeling and Influence Factors Analysis

With the accelerated pace of the electric bus, the growing charging power demand will have a certain influence on the grid. As a precondition of safety operation for power grid, studies on electric bus charging load model are also the theoretical basis of electric bus charging orderly. Firstly, based on the analysis of arriving time and state of energy, power demand model of electric bus charging station was set up. According to this model, electric buses charging station power curve within a day was calculated and presented with the operating data in a demonstration electric bus charging station. The results of the simulation examples show that the modeling method of the charging power demand model is effective.

A New Fault-Positions Method Based on Interpolation for the Area of Vulnerability to Voltage Sags

The area of vulnerability (AOV) of point of common coupling (PCC) can directly reflect the issue of voltage sag caused by faults in power system. In order to calculate the area of vulnerability more accurately and faster, this paper proposes a new fault positions method based on interpolation, which overcomes the blindness of setting fault points. The influence of transformer winding connections on voltage sag is also taken into account. Short-circuit calculation is adopted and transfer matrix representing the transfer law of transformer on voltage sag is deduced firstly. Then, the principle and implementation flow of the new method are presented in detail. Finally, the new method is applied to a regional power system of China, and graphic result of the area of vulnerability is displayed under balanced and unbalanced faults.

Study on Control Strategy of Microgrid in Islanded Operation Mode

The droop control strategy is only considered the frequency stability during the islanded operation mode of microgrid. So a cooperative control strategy based on two-layer hierarchical control structure is proposed in this paper. In islanded operation mode, Single master operation (SMO) or multi master operation (MMO) is decided by microgrid management system (MMS). When power changes during islanded operation, the master unit (s) with v/f control can balance the energy production and consumption quickly. Based on detecting instantaneous power of master unit (s),The secondary control of MMS sets renewed reference values of instantaneous power of slave unit (s) with PQ control. After that the output power of master unit (s) will return into zero. The simulation studies demonstrate that the proposed cooperative control strategy not only implements no-error frequency control and voltage stability control, but also provides enough spinning reserve margin for master unit (s) to keep the system energy balance all the time.

A Control Method to Suppress Resonance and Improve Current Quality for Inverter System with LCL Filter

The LCL filter is easy to resonate, especially in the new energy power system with multiple inverters. The LCL filter resonant formulas are derived in this paper and a novel double closed loop control strategy combing with the structure of the LCL filter was proposed at the base on feedback of capacitor current as a result. In the control system, the inner loop feedback the first differential voltage of filter inductor at the grid side to damp the resonance and nature of first differential voltage of filter inductor is explained; the grid current outer loop achieves direct control of the grid current for high power factor and utilization efficiency. The simulation results show that the grid-side inductor voltage differential feedback control have a better current control effect both in the condition of the normal power grid voltage and distorted grid voltage, and the fluctuations of power and dc voltage are reduced.

Analysis of Current Optimization Method on Compensation

Nowadays, with the rapid development of industrial technology especially the power electronic technology, harmonic and reactive power problems are becoming severer. In sinusoidal conditions, there are no controversies on the definition of power quantities. In nonsinusoidal circuits, the traditional definition of active power is still applicable while the definitions of reactive power and apparent power are in controversy. Based on an optimization current decomposing method, this paper derives the expressions of optimal current and compensating current in a single-phase and a three-phase circuit by constructing a Lagrange functions. Based on simulation studies, the compensating effect of the optimization method is analyzed and shown; it can noticeably improve the efficiency of energy transfer in circuit. The paper presents all mathematical derivation of the method and verifies the results based on simulation.

Influence of Harmonic on the Protections of Capacitor Bank

This paper introduces the capacitor bank equipped with overvoltage protection and overcurrent protection. Then with a group of capacitor for reactive power compensation as the research object, this paper analyses the influence of harmonic to the two protection modes when the electromagnetic, static or microcomputer relay are applied.