Minh Quan Duong

Comparison of power quality in different grid-integrated wind turbines

Nowadays, the proportion of wind turbines and the dimensions of wind plants have increased significantly all over the world. This paper describes a comparison of the power quality for wind power systems based on three different popular wind generators: the squirrel-cage induction generator (SCIG), the doubly-fed induction generator (DFIG) and the permanent-magnet synchronous generator (PMSG). Although a fixed speed system is more simple and reliable, it severely limits the energy output of a wind turbine and power quality. In case of variable speed systems, comparisons shows that generator of similar rating can significantly enhance energy capture as well as power quality. The performances of these wind turbines and their characteristics are analyzed in steady-state. Simulation results matched well with the theoretical turbines operation.

Improving LVRT characteristics in variable-speed wind power generation by means of fuzzy logic

Wind system using a fixed-speed wind power generation SCIG (Squirrel-cage Induction Generator) tends to drain large amount of reactive power from the grid, potentially causing a drop voltage and perhaps voltage stability conundrum. To improve the SCIGs low voltage ride through (LVRT) characteristics, this paper presents a new control strategy for a variable-speed wind power generation DFIG (Doubly-fed Induction Generator) located closely to the SCIG-based wind system by utilizing the control capability of fuzzy logic technique. The proposed control system regulates effectively reactive power output of the DFIG wind turbine by controlling both grid-side and rotor-side converters to compensate the reactive power absorbed by the SCIG-based wind turbine. The effectiveness of the proposed control strategies is proven by simulation results. These illustrates that the LVRT characteristics and stability margin of the SCIG-based wind system is significantly improved when extra reactive power is compensated from the DFIG wind system in the proximity.

Small signal stability of power system with SCIG, DFIG wind turbines

Voltage stability issue is a key problem which attracting worldwide attention because voltage stability may leads to voltage collapse. This paper investigates the impact of Squirrel Cage induction generator (SCIG) and Doubly Fed Induction Generator (DFIG) on the power system small signal stability. Here considered wind generators are SCIG which is fixed speed and DFIG is variable speed. Small signal stability study has been conducted on a modified IEEE 14 bus system with SCIG, DFIG wind turbine systems and their simulation results have been analyzed in this paper. Fixed speed wind generators are more simple to operate and reliable but they are limited as energy output of a wind turbine and stability issues are consider. Variable speed wind generators of similar rating improve stability of the system. All these modelings, simulations have been done in Power system Analysis Toolbox (PSAT), which is a MATLAB based toolbox to evaluate power system.

Performance analysis of a 310Wp photovoltaic module based on single and double diode model

This paper presents a complete simulator developed in Matlab™ for a photovoltaic (PV) module. The most important contributions of the paper is the use of single and double diode model to simulate a PV module. In the paper are also implemented numerical methods to provide more characteristic parameters that are not provided by the manufacturers such as Rs, Rp, Ipv, I01 and I02. The numerical methods are suitably implemented to face the nonlinear nature of I-V and P-V curves that are characteristics to PV output. The accuracy of the simulator using single and double diode models is verified by applying the data-sheet from manufacturers. Furthermore, the double-diode model simulation results performed in Matlab™ are analyzed in comparison with the experimental data of a real 310 Wp photovoltaic module unit. The paper also highlights the effects of different shunt and series resistances and how it operates in different temperature conditions and irradiation levels.

Improved LVRT based on coordination control of active crowbar and reactive power for doubly fed induction generators

This paper proposes a control system, for crowbar protection and voltage support, for wind turbines equipped with doubly fed induction generator. The control system based on PI controller enables the low voltage ride through capability of the wind turbines. The reactive power control of doubly fed induction generators is mostly achieved by controlling its rotor side converter. The proposed control system allows regulating the reactive power using the rotor side converter as well as the grid side converter. During crowbar activation, the rotor side converter can no more control the reactive power. The proposed system controls the voltage at the point of common coupling to be above the imposed low voltage ride through curve, until the grid side converter returns to normal operation. The proposed models were implemented in Matlab/Simulink. The case studies refer to a control system with hysteresis band for the crowbar protection of a 3MW doubly fed induction generator based wind turbine. The simulation results highlights that the proposed control improves the coordination between grid side converter, rotor side converter, and crowbar protection.

High-performance coordination for accurate Matlab Simulink PV module simulator based on a two-diode model

Due to the non-linear nature of diode based PV model, the accurate design of PV module is a difficult task. This paper proposes a comprehensive simulator developed in Matlab and Simulink for a photovoltaic (PV) module using a double diode model. To search extra internal parameters that are not provided by the manufacturers, we have provided numerical methods, suitably implemented to face the nonlinear nature of I-V and P-V curves of the PV output characteristics using Matlab languages. Moreover, a built-in model of PV module is also implemented by authors using Simulink. The accuracy of the simulator using double diode models is verified by applying the data-sheet from manufacturers.

Impact of SCIG, DFIG wind power plant on IEEE 14 bus system with small signal stability assessment

In power systems voltage stability is a key issue which attracts worldwide attention. This research presents an implementation of a modified IEEE 14 bus system model in Power System Analysis Toolbox (PSAT) - free and open source software. A newly developed Squirrel Cage induction generator (SCIG) and Doubly Fed Induction Generator (DFIG) wind turbine model are modeled and connected to a modified IEEE 14 bus system. This paper investigates the impact of Squirrel Cage induction generator (SCIG) and Doubly Fed Induction Generator (DFIG) on the power system stability. Here considered wind generators are SCIG which is fixed speed and DFIG is variable speed. Small signal stability study has been conducted on a modified IEEE 14 bus system with SCIG, DFIG wind turbine systems and their simulation results have been analyzed in this paper.

Hybrid controller for transient stability in wind generators

In wind power plants typically squirrel-cage induction generators (SCIG) tend to drain large amount of reactive power from the grid, potentially causing a drop voltage. To improve SCIGs power quality and transient stability, this paper investigates a new pitch angle control strategy, including normal scheme and Fault-Ride-Through (FRT) scheme, based on hybrid of PI and Fuzzy logic technique. In particular, an analytic model for transient stability is implemented using the equivalent circuit of the SCIG and on the concepts of stable and unstable electrical-mechanical equilibrium. This method has been evaluated by comparing the results with the dynamic simulation. The dynamic simulation results show that the proposed hybrid controller can be effective in enhancing output power smoothness and FRT requirements for SCIG in wind power system.

Effect of component design on the DC/DC power converters dynamics

This paper analyzes the impact of converter design elements on the operating performance of DC/DC converters, used worldwide for renewable energy sources. The design of inductor and capacitor elements is made considering the acceptable output ripple of voltage and current. This paper presents the methodology for determining the inductances and capacitances required for DC/DC converter operation within the acceptable power system limits. Simulations are carried on for investigating the dynamic stability of DC/DC converter.

Optimal bypass diode configuration for PV arrays under shading influence

Under partial shading conditions caused by the unevenly radiation and other ambient environmental conditions the operation of solar cells is influenced. Depending on the degree of shading, the phenomenon causes the decrease of solar cells output power. In the present paper two bypass diode configurations are compared, PV module with a bypass diode across each cell and with a bypass diode across each group cell, which are the most studied in the scientific literature. A PV module with analyzed bypass configurations was implemented in PSpice. This paper analyses the effects of bypass diode configurations on photovoltaic systems operation under various shaded degrees. The simulation results reveal that both solutions can limit the effects of this shading phenomenon and thus enhance the operational performance of photovoltaic (PV) systems. Further, the analysis of simulation results for I-V and P-V characteristic curves highlight the advantages and disadvantages of each type of bypass diode configuration, and also their use in practice.