Lingzhi Zhu

Simulation study on transient characteristics of DFIG wind turbine systems based on dynamic modeling

The paper analyzes the transient characteristics of DFIG wind turbine systems based on different types of dynamic model and different control strategy. The differential equations corresponding with the equivalent circuits of the DFIG wind turbine systems such as the third-order simplified DFIG model are derived and implemented in Matlab/Simulink. The one-mass shaft model and two-mass shaft mode which are widely used in power system impact studies are implemented too. Under different control strategies such as constant voltage control mode, constant var control mode, the time-domain simulation is carried out. Through simulation results, it provides transient characteristics of DFIG wind turbine systems, which have illustrated the fact that the type of wind turbine model largely affect the mechanical characteristics such as rotor speed and affect low voltage through feature further. It also provides suggestion for DFIG wind turbine systems dynamic model reduction for the large-scale wind farm voltage stability analysis.

Impact of disturbance method on parameter identification of photovoltaic inverter model

With large scale grid-connected photovoltaic (PV) generation, it plays a more and more important role in power system, while the investigation of PV integration problem and solution is based on accurate model parameters. In this paper, the inverter model is introduced and model parameter sensitivity is analysed under different disturbances. Then the impact of disturbance method on parameter identification of PV inverter is discussed. Three disturbance cases are simulated to provide data for identification, and the identification results from these cases are compared. The analysis conclusion is useful for experimental design. Finally, the parameters of an actual inverter are identified based on experimental data.

Preliminary investigation on effect of PV generation on oscillation modes of power system

Capacity of grid connected photovoltaic (PV) power has increased significantly over the recent years in China, a significant number of large-scale PV plants have been put into operation, such as Golmud (300MW) and Long-yang Gorge (320MW) in Qinghai province. These PV plants are always geographically far from load centers and connected to relatively weak transmission networks. Whether these large PV plants will have an impact on the oscillation modes of power system? If yes, what is the impact? They are all still open questions and worthy of further investigation. In this paper, firstly, typical structures of PV plant integration system are designed, including chain and ring structures. Secondly, based on the typical structures, two influencing factors, namely PV penetration level and electrical distance of PV plant from power system, are chosen to investigate the impact of PV plant on power system oscillation modes. The analysis results based on DIgSILENT PowerFactory software have been listed and compared under the two system topology structures.

Active and Reactive Power Control of Wind Farm Based on Integrated Platform of PowerFactory and MATLAB

The integration of large-capacity wind energies into a power system creates big challenges to the power system operation and control due to the intrinsic intermittence of wind energies, which constrains further developments of wind power generation. Countries around the world including Europe, USA and China have all made Grid Codes with clear requirements on active and reactive power controls in a wind farm. By effective active and reactive power controls, wind power curtailments can be substantially reduced. Furthermore, there have been no mature simulation and analysis platforms in China on testing correctness and rationality of wind farm control strategies so far. This chapter reports our research as well as engineering practices on building an integrated active and reactive power control system for wind farms using PowerFactory and MATLAB. The highlights that make this work unique are as follows: (i) the integration of PowerFactory and MATLAB makes the active and reactive power control modelling efficient and flexible; (ii) both the real measurements of wind speeds and the active power forecasted from history data are inputted in text file format to each wind generator in PowerFactory; (iii) the reactive power control capabilities of wind generators are fully utilized to reduce the scale of the reactive power compensations installed in a wind farm or from the grid.

Investigation on power control validation system of wind plant based on measured data

The accuracy of wind plant power control strategy is the key to ensure the adaptability of the wind plant. Effective testing and verification are essential means for the correctness of the control strategy. In this paper, the principle of active and reactive power control system for wind plant is studied firstly, the implementation architecture of power control system of wind plant is analyzed then, the modules of the power control system of the wind plant is implemented according to the modular design thirdly. Finally, a wind plant model with practical engineering background is established to validate the feasibility of the proposed wind plant power control system by injecting the measured data.

Model validation of a wind farm using hybrid data simulation

Model accuracy of wind farms is the key factor to investigate the mutual influences between them and a power grid. However, this problem has not been well solved, especially in how to apply the real measurements to validate the models of wind farms. This paper presents a model validation methodology for wind farm via the hybrid data dynamic simulation. First, several typical hybrid data simulation methods are introduced and variable impedance method of them is especially described, merits of it is analyzed. Second, the implementation scheme of variable impedance method is investigated in DIgSILENT PowerFactory. At last, a real application via the variable impedance hybrid data simulation method in power system of north China is studied, which illustrates the effectiveness of the hybrid data simulation method in wind farm model validation.

Modelling and simulation of the solar photovoltaic systems for grid studies considering the negative sequence control strategy

One of the main trends in the development of solar photovoltaic (PV) grid-connected technology is the in-depth study of modelling the PV system and simulation for the transient characteristics. But the commonly used dynamic models are not available for the electromechanical transient (RMS) unbalance simulation. This paper presents an improved model which is based on the GE solar plant model for asymmetric fault. Firstly, It derives the differential equations correspond with the equivalent circuits of the PV system and extends the frame of the model which can contain the positive negative and zero sequence (PNZ-seq.) network. The converter block is redesigned to provide an interface between the PV system and the multiphase (balanced or unbalanced) network. Then, it emphasis on the control block which dictates the active and reactive power to be delivered based on command. The innovative improvement is to consider the P-Seq. and N-Seq. coordination control strategy for RMS unbalance simulation. Finally, the improved model is implemented in the DIgSILENT PowerFactory software. The simulation results have illustrated that the improved model can more accurately reflect the transient characteristics and contribute to a more accurate stability analysis of large PV system connected to the grid.

Safety Impact of Large-Scale Distributed PV Power Access to Power Grids

 Abstract—Photovoltaic (PV) power generation is the fastest growing part of distributed generation technologies. Large-scale PV power connected to the grid is bound to the safe operation of the grid to bring new problems and challenges in China. Based on PSASP, combined with large-scale PV power access to the actual grid, this article establish PV model, do research on the characteristics of large-scale PV power stations and network system. In this article, the characteristics of PV grid-connected systems, stability and other issues accessing to large-scale PV system are discussed.

Modeling Comparison on Control System of Synchronous Generator between DIgSILENT Power Factory and PSASP

 Abstract—PSASP is a widely used power system analysis program in China, and it provides various measured models and corresponding parameters of synchronous generators control system. DIGSILENT Power Factory is a popular power system analysis software package around the world. In this paper, some commonly used models in PSASP are established in DIGSILENT Power Factory. The contrast effect is implemented by conducting small perturbation and large disturbance in a two-area four-machine system at last.

Calculation of harmonic suppression and reactive power compensation device's capacity configuration in electric vehicle charging Stations

The high-power rectifiers in electric vehicle (EV) charging stations may bring serious harmonic pollution to power grid. For different types of EV charging stations, one of the issues concerned in the engineering is that how much capacity of the active power filter (APF) and reactive power compensator should be configured. Previous research has given preliminary configuration principle and calculation formula of the APFs capacity. On this basis, based on the configuration parameters of typical EV chargers and charging stations, firstly, this paper gets the maximum harmonic current and power factor values in the output voltage range of the different EV chargers by doing lots of simulations. Secondly, the capacity of APF and reactive power compensator needed for single EV charger is calculated. Thirdly, the mathematical formula of APFs configuration capacity for the whole EV charging station is presented. Finally, the configuration capacitys calculation results of APF and reactive power compensator for different EV charging stations are given.