Jiazhu Xu

A New Converter Transformer and a Corresponding Inductive Filtering Method for HVDC Transmission System

A new converter transformer and an inductive filtering method are presented to solve the existing problems of the traditional converter transformer and the passive filtering method of the high-voltage direct current (HVDC) system. It adopts the ampere-turn balance of the transformer as the filtering mechanism. A tap at the linking point of the prolonged winding and the common winding of the secondary windings is connected with the LC resonance circuit. It can realize the goal that once theharmonic current flowsinto the prolonged winding, the common winding will induct the opposite harmonic current to balance it by the zero impedance design of the common winding and the proper configuration of LC parameters, so there will be no inductive harmonic current in the primary winding. Moreover, the reactive power that the converter needs can be partly compensated in the secondary winding. Simulation results have verified the correctness of the theoretical analysis. The new converter transformer can greatly reduce the harmonic content in the primary winding, loss, and noise generated by harmonics in the transformer, and the difficulty of the transformers insulation design.

Study on Characteristic Parameters of a New Converter Transformer for HVDC Systems

Different from the traditional converter transformer and ac passive filtering method, this paper presents a new converter transformer and a corresponding inductive filtering method for HVDC systems. Based on this, characteristic parameters of the new converter transformer are studied in detail by theoretical analysis, simulation, calculation, and experimental verification. By deducing voltage relation, the constraint condition of the turn ratio is obtained, which can satisfy the demand of a 12-pulse converter in HVDC systems. By deducing current relations, the characteristics of the fundamental and the harmonic currents in the winding are obtained. According to the established operation equations, the simple but practical calculation methods for the short-circuit impedance and the rated capacity are proposed. Then, the change characteristic of the short-circuit impedance is analyzed and calculated. The detailed simulation and test results verified the correctness of the aforementioned theoretical analysis and calculation.

An Industrial DC Power Supply System Based on an Inductive Filtering Method

This paper proposes a new direct current (dc) power supply system based on an inductive filtering method for one industrial dc load. The operating mechanism of the new inductive filtering method is analyzed, and then, the harmonic model and the equivalent model are established. Moreover, the impedance conditions for the implementation of the inductive filtering method are presented, and the influence of the filtering loops impedance on the filtering performance is clarified. Both the simulation and the experimental study on one practical inductive-filtering-based industrial dc supply system for chemical electrolysis are used to validate the theoretical analysis. The research results show that the inductive filtering method not only greatly reduces the harmonic magnetic flux in the rectifier transformer but also prevents harmonic currents from flowing into the primary (grid) winding of the rectifier transformer. It presents good filtering and reactive power compensating performances to public networks and also increases the operating efficiency of the industrial dc power supply system itself.

Harmonic characteristics of new HVDC transmission system based on new converter transformer

The study on the harmonic characteristics of HVDC transmission system is important for analyzing the effect of harmonics on the operation of the electrical installation and the system. The new HVDC transmission system adopts the new converter transformer and the corresponding inductive filtering method, and it is a new electrical topological structure. As for a new system, the harmonic characteristics of the new HVDC transmission system are completely different from that of the traditional one. This paper introduces the main circuit topology of the new HVDC transmission system, and then analyzes the connection of the new converter transformer and the filtering mechanism of the inductive filtering method. Based on these, the mathematic model has been established to calculate the harmonic characteristics of the new HVDC transmission system. Furthermore, the amplitude and phase angle of the main characteristic harmonics of the new HVDC transmission system have been calculated by the established mathematic model and then simulated by MATLAB/SIMULINK. Tested results have verified the correctness of above analysis and calculated results. The research findings are useful for the design of the characteristic parameters of the new HVDC transmission system, the selection of the wire cross-section of the new converter transformer, and the design of the inductive filtering installations.

A Novel Method of Harmonic Suppression in the AC/DC Transmission System Based on Novel Converter Transformer

In the traditional AC/DC transmission system, to reduce the effect of harmonics to the AC system produced by the converter, filters and reactive power compensating equipments are installed in the primary side. This article presents a novel converter transformer and harmonic suppression scheme- filter commutated converter (FCC), which can greatly restrain the harmonic current from flowing into the AC system. The article also introduces the connection mode of windings, calculation of voltage offset angle, determination of windings turn ratio and request of windings equivalent impedance; and it analyzes the harmonic suppression principle, too. Finally, it establishes the digital simulation models of DC transmission system based on the novel converter transformer and traditional converter transformer. The simulating results of frequency spectrum of current wave indicate that the 5th , 7th , 11th and 13th harmonic components can be effectively suppressed in the valve side with FCC. Compared with the results of the traditional harmonic suppression, the reliability and feasibility of the novel converter transformer and the scheme of harmonic suppression (FCC) are testified.

LMI-based robust wide-area time-delay damping control of SSSC-type FACTS device for stability enhancement of power system

This paper presents a linear matrix inequality (LMI) method for the design of the wide-area time-delay damping (WATDD) controller of static synchronous series compensator (SSSC)-type flexible ac transmission system (FACTS) device to enhance the power stability of the interconnected power systems. Firstly, in order to reveal the single-input multi-output (SIMO) characteristic of the open-loop power system with SSSC-type FACTS device, the prediction error estimation (PEE) algorithm based system identification method is applied to fit a special SIMO linear model. Then, based on the robust control theory and LMI method, the identified linear model is formulated as the standard control problem with the time-delay of the input signals of the WATDD controller, and combined with the designed state observer for the input state variables of the WATDD controller, the control parameters are optimized by the LMI iterate solution algorithm. Finally, the nonlinear simulation on the typical 2-area 4-machine system installed with SSSC-type WATDD controller is performed to verify the LMI-based design method and the proposed SSSC-type WATDD controller.

Transient response characteristics of new HVDC transmission system based on new converter transformer

The new HVDC transmission system adopts the new converter transformer and the corresponding inductive filtering method, and its electrical topology structure is completely different from that of the existential HVDC transmission system. For the change of the controlled system, the transient response characteristics of the new HVDC transmission system will be accordingly changed when it adopts the standard control model that the traditional HVDC transmission system adopts. Referring to the parameters of the main circuit of the OGRE HVDC first benchmark model, this paper designs a similar benchmark model of the new HVDC transmission system based on the technical characteristics of the new converter transformer and the corresponding inductive filtering method, which mainly contains the rated parameters of the new converter transformer and the inductive filtering device. Then, the typical transient response characteristics of the new HVDC transmission system have been analyzed and simulated by PSCAD/EMTDC. The results express that the new HVDC transmission system, which adopts the standard control model that the HVDC transmission engineering adopts, has a good transient response characteristic, and can operate stably when subjecting to various typical disturbance.

Transient Simulation of the AC/DC System Based on the New-type Converter Transformer

For announcing the electromagnetic transient course of the auto-compensator and harmonic shielding converter transformer, simulating the new-type converter transformers voltage, currents input and output characteristics in the HVDC system and the interaction of the AC/DC system, This paper establishes the new-type converter transformers transient simulation mathematic model using the synthetic companion method and the controlled source theory, and the simulation experiment is carried on by applying this model into the HVDC transient simulation. The experimental results show that the new-type converter transformer optimizes the systems structure in the certain degree. Through the zero impedance design of the third winding and the filter parameters reasonable setting, it not only can greatly reduce the harmonics in the AC side and the loss to the converter transformer, but also improve the converter bridge AC sides voltage and current wave, which is advantageous to the converters normally moves.

Characteristics of power transmission and dynamic recovery of FCC-HVDC with different SCR

HVDC transmission systems are widely used in China. Using the software of PSCAD/EMTDC, the model of FCC-HVDC is established referring to the CIGRE benchmark model of HVDC. The principle of FCC in this model is described, and the models of LCC-HVDC and FCC-HVDC are presented. Then this paper introduces contrast tests under two typical disturbances: A-phase ground fault and shutting degree generating +5°step on the inverter side. Active power of the rectifier station and inverter station with the same short circuit ratio (SCR) are analyzed respectively, also dc power of the rectifier side and inverter side are analyzed. Consequently, the characteristics of power transmission and dynamic recovery of FCC-HVDC under different conditions are studied. In the last, the simulation results show that FCC-HVDC may improve the capacity of DC transmission, and keep relatively satisfactory dynamic recovery characteristics under the conditions of various typical disturbances as mentioned above.

Harmonic Elimination Using Parallel Delta-Connected Filtering Windings for Converter Transformers in HVDC Systems

In conventional HVDC systems where the harmonic filters and shunt capacitors are installed at the ac grid side, the converter transformers inevitably suffer the detrimental impacts caused by harmonic penetration. In this paper, combined with an inductive filtering method, a parallel delta-connected filtering-winding scheme for 12-pulse converter transformer units is proposed to reduce the harmonic currents flowing through the transformers and, thus, to attenuate the harmonic effects on them. This paper describes the presented transformer configuration in terms of the wiring scheme of the 12-pulse converter transformer unit and corresponding flowing paths of different harmonic currents with the orders of