Luo Longfu

LCL output filter design and the influence to the D-STATCOM compensation characteristic

As an important dynamic compensation device, the D-STATCOM is widely used in the power system, but its output current contains a lot of high-frequency harmonic composition. The LCL filter, a typical output filter, has good filter characteristics, but the compensation characteristic of D-STATCOM has strong sensitivity to the filter parameters. The paper firstly analysis the influence caused by the components of the output filter. Considering the compensation capacity of the D-STATCOM, the compensation current switching ripple, the grid THD, the resistance loss and the other factors, a method of designing LCL filter was presented, and then analysis the compensation characteristic of the D-STATCOM with the LCL filter, the results proved that the output filter designed in this method has very good inhibitory effect on high-frequency switching ripple, and greatly improved the compensation performance of the D-STATCOM.

An improved droop control strategy in the islanding operation

For maintaining the stability of voltage and frequency, the droop control is often adopted when micro-grid is in islanding operational mode. Although this method can control the fluctuation of voltage and frequency, when the loads change, its implementation effect is weak In order to solve the mentioned problem, an improved dynamic self-adjusting droop control strategy is proposed: on the basis of the traditional one, PI control of voltage and frequency is introduced to control flow. The principle and implementation steps of this method are analyzed. Finally, the operating characteristics of overloading connection, overloading cutting-off and loads disturbance are simulated and discussed based on an islanding mode built in Matlab/Simulink. The results show the proposed method can control the voltage and frequency more effectively and faster than traditional droop control, and can enhance the stability of micro-grid in islanding operational mode.

Heat analysis of main high-speed electric locomotive transformer tank using 3-D finite element method

It is necessary to accurately calculate the tank loss and local hot-spot temperature rise because of intense transverse leakage magnetic field in the high-speed electric locomotive main transformer with interleave windings and high leakage impedance. In this paper the leakage magnetic field of the main transformer has been analyzed. The eddy loss in the tank has been calculated accurately. The temperature field of the tank wall has been simulated and the hot-spot and corresponding temperature rise has been found. Based on these, the corresponding shielding measure has been brought forward.

A new modular multilevel type solid statetransformer with internal model control method

To overcome the limitation of the existing topologies and control strategies of Solid State Transformers, a Modular Multilevel Converter type solid state transformer (MMC-SST) topologies and its corresponding internal model control (IMC) method is introduced in this paper. Firstly, the structure and operation characteristics of MMC-SST were analyzed, and accordingly its mathematical model of input and output-stage in synchronous rotating d-q frame was established. Secondly, a new kind of duel-loop control structure was developed by combining the IMC current inner loop and PI voltage outer loop, according to the characteristics of IMC. Lastly, a simulation model of MMC-SST was established based on Matlab/Simulink, the grid side voltage amplitude mutation, load capacity transient and grid side power factor change in various conditions are simulated. Results show that the MMC-SST based on internal model control can run under different power factor, as well as the fast transient response of voltage and current , strong ability to resist load disturbance characteristics, and can improve the robustness of the system.

Negative Sequence and Harmonic Suppression Unified Control Method for High-Speed Electric Railway

Due to the negative sequence and harmonic currents power quality problems caused by high-speed electric railway traction power supply system, this paper proposes a new type of negative sequence and harmonic unified control method, which is based on the transformer inductive filtering technology. Three-phase V/v traction transformer, combination of a inductive filtering technology and SVG system, the former is used to suppress characteristic harmonics, the latter is used to compensate negative sequence and residual harmonics. Based on ampere-turn balance principle, it fulfills the total elimination of negative and harmonic magnetic potential, so that the network side does not contain the corresponding negative sequence and harmonic currents. After analysis on the basic principle, the simulation results prove the correctness and validity of the unified control method. This method fully exploits the electromagnetic potential of traction transformer, it not only plays the role of power transmission and transformer, but also can be used for power quality control, eventually forming a transformer system that owns the function of harmonic shielding and negative sequence control.

Starting process simulation of Smith single-phase capacitance motor

A transient mathematical model of Smith single-phase capacitance motor was established, and the starting process of Smith single-phase capacitance motor was analyzed. Smith single-phase capacitance motors due to wiring constraints, the maximum voltage of each phase winding is 0.577 times the supply voltage, unique values capacitor starting torque when starting small, dual-values capacitor start can effectively improve the starting torque, shortening start-up time, but double the number of capacitors. In view of this situation, proposed a new start wiring methods, not only to improve starting torque, but also to reduce the number of capacitors, reducing investment costs, improve operational reliability. The simulation program was complied according to the mathematical model by Matlab. The starting processes of some startup methods of Smith single phase motor are simulated and calculated by examples such as unique values capacitor startup method, dual-value capacitor startup method and the proposed startup method, and the simulation results of these methods are contrasted and analysed. Both verify the correctness of the proposed method.

Application prospect of a new transformer inductive filtering technology

Different from passive and reactive filtering methods, this paper proposes a new transformer inductive filtering technology. Its characteristics is that it develops the potential electromagnetism capability of the transformer and makes use of the ampere-turn balance action of the interior coupling winding, which can suppress the harmonics in the secondary winding and avoid the harmonics flowing into the primary winding. In addition, it can effectively abate the negative effect of the harmonic magnetic potential on the transformer. This paper introduces three types of new supply transformers, expounds the interrelation and combined technical characteristics, then expands on its research progress and the industrialization condition. Furthermore, the paper summarizes the practical significance of new inductive filtering technology and its application prospect. The author adopts systematic analysis method, and carries out systematic research for the transformer inductive filtering technology. By means of various model experiments analysis, it verifies the good filtering influence that the new inductive filtering technology has.

Designing and simulating for research of filtering of direct current transmission system based on novel converter transformer

The characteristic to shield harmonics of the novel converter transformers is presented in this paper. Then design the DC transmission system of the novel transformer to achieve harmonics shielding function, by adopting the novel transformer on the rectifier side. Based on the calculation method of harmonic content in the HVDC system, calculate and allocate the reactive power compensation on both the rectifier side and inverter side on the experiment platform, according to which a variety of filters parameters are designed. Final, simulation to DC transmission system is carried on, and the result indicates that the harmonics shielding function can be achieved using the novel converter transformers, which has certain value in use in the engineering.

Load Characteristics Analysis of the Primary Side of Three Typical Traction Transformers with Various Power Factor Definitions

Aimed at the nonlinear, asymmetric and fluctuant characteristics of the traction loads, this paper researches and analyzes the loading characteristics and power factor values of V-V, Y-D11 and Impedance-Matching traction transformers by a novel approach. Four definitions of power factor are compared-three considering harmonics and unbalances and one base only on fundamental components. This paper verifies the Impedance-Matching transformer superiority on restraining imbalance from power factor. The simulation results and actual measurement data reveal that, compared with other power factors, according to distort and imbalance, the effective power factor could be recommended for use in fairly evaluating the load characteristics for traction transformers.

The harmonic analysis of traction power system based on a new Vv traction transformer

Traction power system of electrical railway has nonlinear loads, which produces a great quantity of harmonics which will affect power quality of grid unavoidably. For Traditional Vv transformer does not have filtering capacity, all the harmonics are delivered to the grid. In this paper, a new Vv transformer that has filtering capacity is raised. What is more, its equivalent circuit and harmonic model are proposed, and its filtering theory is analyzed. At the end, the simulation model of the traditional Vv and the new Vv wiring transformers in the traction power system are established and the harmonic character is analyzed. The simulation results show that, the new Vv transformer can suppress the harmonics at its traction side effectively, lower harmonic content of grid side, and lower harmful influence of harmonic to traction transformer.