Li Gengyin

Power flow calculation of power systems incorporating VSC-HVDC

Voltage source converter (VSC) based HVDC (VSC-HVDC) technology is a kind of newly developed HVDC transmission technology. This paper makes detailed analysis to the basic principle and the structure of VSC-HVDC, and sets up the steady-state mathematical model of VSC-HVDC, under fixed control parameters and fixed power flow control objectives respectively. Then a novel algorithm for power flow calculation based on equivalent injection power is deduced. A power flow calculation program of power systems, incorporating VSC-HVDC transmission lines and multiterminal VSC-HVDC networks, is developed based on the user programming interface (UPI) of power system analysis software package, PSASP/UPI. Numerical examples of EPRI 7-bus test system with a 2-terminal VSC-HVDC line and a test system with 3-terminal VSC-HVDC network are given. The results show that the proposed steady-state model of VSC-HVDC and corresponding power flow calculation based on PSASP is correct and effective. This software package provides a powerful tool for planning, design, operation, management, and relative control strategy studies of VSC-HVDC systems.

Modeling of VSC-HVDC and its active power control scheme

The paper presents an equivalent continuous-time state-space model in the synchronous dq reference frame for VSC-HVDC. Based on the model, a power controller is designed to follow command signals. A multi-input multi-output (MIMO) control scheme is developed in the paper. The scheme features feed forward compensation to eliminate the coupling between the d- and q-axis of the voltage source converter (VSC) model. Also, the response speed of the controller can be accelerated by introducing a derivative to the active power loop. With the simulation using PSCAD/EMTDC, the validity of the mathematic model and the feasibility of the power controller have been proved.

Research on hybrid HVDC

Based on analysis of the development, technology characteristics and application scope of conventional HVDC and voltage source converter based HVDC (VSC-HVDC), an alternative form of HVDC transmission, named hybrid HVDC, is presented in this paper. At first the fundamental principle and technology characteristics of hybrid HVDC are analyzed, then the simulation model is founded based on simulation software PSCAD/EMTDC. Simulation results show that the proposed hybrid HVDC system can be operated steadily. Further more when two AC sides have single phase to ground or three phases short circuit fault in short time it has the capability to restore steadily and rapidly. At last the advantages and disadvantages of the hybrid HVDC and its application foreground are evaluated.

A novel power flow tracing approach considering power losses

This paper proposes a new approach on tracing power flow and losses simultaneously, which is based on proportional sharing principle. Each node is equivalent to two nodes, an active power node and a reactive power node. Then a proportional sharing matrix M is built up. To trace power flow, searching this matrix gets the contribution factors of each generator and each line-to-ground capacitance to each load. During the process of tracing, line charging power is equivalent to reactive power source in the both ends of a line, and loop flow is detected and settled. Numerical test shows that the proposed method can trace both power flow and losses correctly and effectively, which provides foundation for transmission charge allocation.

A multi-agent based dispatching operation instructing system in electric power systems

Fault section identification and switching operation are two important tasks for electric dispatching operators in power systems. Now electric supply industries are undergoing restructuring and deregulation, and the operation modes are getting more complicated, electric components are operating near to their security limits along with the probability of fault increasing largely, and operation modes changing more frequently. Automatic fault section identification and expert-system-based switch operation instructing system are much helpful to improve the intelligent level of dispatching operation. At present automatic fault section identification system (AFSIS) as aided decision-making for the operators is put into the field, switch operation instructing system (SOIS) also does. But these systems almost belong to a single agent, with power systems rapidly expanding, they have exposed to some limits. On the basis of research on AFSIS and SOIS for many years, a multi-agent system (MAS) based dispatching operation instructing scheme is proposed in this paper. The cooperation between AFSIS and SOIS is the key problem to study. A task decomposing method based on structural property, and a hybrid coordination control strategy is presented. More researches are focused on MAS task decomposition, coordinated control, data share, communication implementation and MAS learning. A MAS-based dispatching operation instructing system (MASDOIS) is implemented and put into the field. The field application shows MASDOIS more advantageous than individual agent in the sides of integrated solving problems, cooperative control and information share.

An adaptive BP-network approach to short term load forecasting

This paper proposes an adaptive BP-network approach to short term load forecasting (STLF) in a deregulated environment, which is to determine the BP-network structure using genetic algorithm (GA). The aim is to optimize the network structure and improve the accuracy of STLF. The realization process consists of three steps. In the first step, the number of hidden nodes of BP-network is calculated by use of GA. In the second step, by use of GA a fittest initial weight value is selected from the solution group of initial weight values to avoid the blindness in the selection of initial weight value. In the third step, combining the structure of the obtained BP-network and the fittest initial weight value, the STLF of power system can be performed by use of improved BP algorithm. Simulation results show that the percentage errors of mostly of 24 h forecasting load are less than 3%, and prove that the approach can meet the need of forecast accuracy and enhance the performance of the network.

Calculation of three-phase harmonic power flow in power systems with traction loads

The mathematical model of an SS4 type electric locomotive, made in China, is first introduced. By considering the harmonic source as a controlled current source, a new algorithm of solving three-phase asymmetrical harmonic power flow in power systems with traction loads is presented. In this scheme, the three-phase fundamental power flow is solved by the P-Q decoupled method in which sparse and symmetrical matrix handling technology and a three-phase factor table are used; thus memory is saved and computing quantity is decreased. The three-phase harmonic power flow is directly solved by the Gaussian elimination method with a linear nodal voltage equation and thus the convergence problem does not exist. The fundamental and harmonic nodal voltage and branch current are solved by the decoupled iteration of fundamental and harmonic power flow. Computation results of some typical examples show that this algorithm can effectively save memory and has good convergence.

Research on daily trading plan considering spinning reserve in power market

Considering the trend of simultaneous existence of electricity market and ancillary services market, this paper proposes an integrated bidding model of electric energy with ancillary service, and presents a solving method based on network flow programming method. The pricing of ancillary service and distribution scheme is then determined. A practical software for daily trading plan considering spinning reserve in power market has been developed. Some typical examples are tested and analyzed The comparison results between the proposed approach and separated bidding method show that both proposed model and solution are correct and effective.

The study on the VSC control of TCSC for damping power system low frequency oscillation

This paper introduces a method of establishing a linearized mathematical model of multimachine power systems with thyristor control series compensation (TCSC). Based on the linear model, the variable structure control (VSC) scheme of TCSC is proposed for improving the damping performance of low frequency oscillations. The results of simulation studies show that the dynamic stability of power systems is significantly improved by the VSC controller over a wide range of operating conditions.

Analysis and management system for power system fault information based on intranet network

Using Internet network technique, database technique and object-oriented design method, a comprehensive analysis and management system for power system fault information is developed and a feasible network connection project for fault information connection is put forward. The fault analysis functions, e.g., fault diagnosis and location, supervisory and judgment to equipment operation, harmonic analysis and waveform treatment, etc. are developed. Fault information management system is also set up, and easy inquiry and browse based on the Web is developed. The practical application shows that the proposed system makes the information be wide share and promotes operation automation.