Yanzhang Liu

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.

Study on modeling method of renewable energy generation system based on control mode and strategy switching

According to the diversity of control structures and complexity of modeling methods for power electronics grid-connected devices of typical renewable energy generation system, a model of renewable energy generation system with a static generator as the grid-connected interface was proposed. In the process of simulation, the control strategies of the active power and the reactive power could be switched by changing the states of the mode control switches in the modules. Finally, the adaptability of the model for different forms of renewable energy generation system was verified. The results showed that the model with modular feature had correct action logic and reasonable simulation waveforms, could represent a specific kind of control system structure and control strategy for different forms of renewable energy power generation system with power electronic devices as the grid-connected interface.

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.

Study on control characteristic of grid-connected solar photovoltaic plant based on simulation

Along with the advancement of renewable energy development strategy, photovoltaic (PV) power technology has gained rapid progress in recent years. Due to the rapid growth of PV power penetration in power system, the research with PV power grid integration are drawing more and more attention, such as low voltage ride through (LVRT), automatic voltage control (AVC), voltage stability and so on. This paper investigates on voltage and reactive power control characteristic of grid-connected solar PV plant based on simulation. The voltage and reactive power control strategy uses the grid-connected inverters and static VAR compensation (SVC) device as flexible and controllable source of reactive power to regulate the voltage and reactive power of large-scale PV power plants. The PV inverters and SVC both have a variety of control mode generally, such as constant voltage control mode, constant reactive power control mode, constant power factor (PF) control mode and so on. The coordination control characteristic between PV inverter and SVC is analyzed in this paper. Through in-depth study of the characteristics of different combinations of control modes, the operating characteristics of PV power plants are summarized. The research results of this paper are helpful to the development of AVC sys tem.

Modeling and implementation of direct-drive permanent magnet wind turbine based on generator parameter conversion

Accurate wind turbine model is the basis of studying its dynamic physical process and performance characteristics. In order to resolve the difficulties in modeling direct-drive permanent magnet wind turbine (DD-PMWT) because of the absence of permanent magnet synchronous generator (PMSG) model in some existing power system analysis software, the method to interconversion between electrical excitation synchronous generator (EESG) and PMSG was presented as well as the parameter conversion formulas and procedure were provided on the basis of their mathematical model and equivalent circuit in this paper. In additon, the model of DD-PMWT was built in DIgSILENT PowerFactory by means of replacing PMSG with EESG. Finally, based on the typical test system provided by Western Electricity Coordinating Council (WECC), the dynamic characteristics of DD-PMWT were analyzed. The simulation results verified the validity of the proposed method and the rationality of the established DD-PMWT model.

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.