The growing trends in wind energy technology are motivating the researchers to work in this area with the aim towards the optimization of the energy extraction from the wind and the injection of the quality power into the grid. Over the last few years, wind generators based on permanent magnet synchronous machines (PMSMs) are becoming the most popular solution for the modern wind energy conversion systems (WECSs). This paper presents a concise review of the grid-integrated WECSs employing permanent magnet synchronous generators (PMSGs). It reviews the trends in converter topologies, control methodologies, and methods for maximum energy extraction in PMSG based WECSs, which have been reported in various research literatures primarily in reputed research journals and transactions during last few years. It also presents an overview to the grid interconnection issues related to output power smoothing and reactive power control in addition to fault-ride-through (FRT) and grid support capabilities of PMSG based WECSs. This review article will serve the researchers working in the area of grid-integrated PMSG based WECSs in the exploration of trends, developments and challenges in the past research works and in finding out the relevant references for their research work.

Grid-integrated permanent magnet synchronous generator based wind energy conversion systems: A technology review

A novel algorithm for fundamental frequency and harmonic components detection is presented in this paper. The technique is based on a real-time implementation of discrete Fourier transform, and it allows fast and accurate estimation of fundamental frequency and harmonics of a distorted signal with variable fundamental frequency. It is suitable for active shunt filter applications, when fast and accurate tracking of the reference signal is required to achieve a good control performance. The main application for the algorithm is aircraft ac power systems, where the fundamental frequency can be either fixed on 400 Hz and its actual value fluctuates around the nominal value, or variable in the range 360-900 Hz. Hence, a real-time estimation of fundamental frequency is essential for active filter control. The proposed algorithm has been at first implemented in Matlab/Simulink for computer simulation, and it has been compared with a Phase Locked Loop (PLL) algorithm for frequency detection and the synchronous dq reference method for harmonic detection. Experimental tests have been carried out in order to validate the simulation results. The distorted current absorbed by a nonlinear load is analyzed and processed by means of a digital implementation of the algorithm running on the active shunt power filter control DSP, in order to calculate the active filter compensating current.

Real-Time Estimation of Fundamental Frequency and Harmonics for Active Shunt Power Filters in Aircraft Electrical Systems

An active-damping strategy is proposed for the suppression of speed and torsional oscillations in permanent-magnet synchronous generator (PMSG)-based wind-energy conversion systems (WECSs). Direct-driven configuration with PMSG is an attractive choice for WECS because of the gearbox elimination and cost reduction due to small pole-pitch design. However, speed and torsional oscillations appear when the generator is directly connected to the wind turbine without any assistant damping device. Based on small-signal analysis, a low-bandwidth design for the power or generator torque controller of PMSG can help to reduce the oscillation amplitude, but the system dynamic performance is thus sacrificed. From the power-flow's point of view, the oscillation is reflected in the dc-link current. With the help of switch function modeling based on the space-vector-modulation scheme, the average dc-link current can be estimated and applied to the compensation strategy, which provides positive damping resulting in stability improvement. The simulation and experiment results verify the theoretical analysis and the validation of the proposed strategy.

Active Damping for PMSG-Based WECS With DC-Link Current Estimation

Energy management of flywheel-based energy storage device for wind power smoothing

A new approach using field-programmable gate array (FPGA) to implement a fully digital control algorithm of active power filter (APF) is proposed in this paper. This FPGA-based controller integrates the whole signal-processing function of an APF, including synchronous-reference-frame transform, low-pass filter, three-phase phase-locked loop, inverter-current controller, etc. By case studies on the principle, performance, and architecture, these control blocks are implemented in real-time and synthesized into a medium-scale FPGA chip by adopting some useful digital-signal-processing techniques, such as pipelining, folding and strength reduction, with respect to minimization of hardware resource and enhancement of operating frequency. As a result, the whole algorithm needs around 5000 logic elements and can run at synchronous system-clock rates of up to 65 MHz. Experimental results on a laboratory prototype are given to demonstrate performance of the proposed approach during steady-state and dynamic operations.

Steady-State and Dynamic Study of Active Power Filter With Efficient FPGA-Based Control Algorithm

Grid-connected wind turbines are fluctuating power sources that may produce flicker during continuous operation. This paper presents a simulation model of a megawatt-level variable-speed wind turbine with a full-scale back-to-back power converter developed in the simulation tool of PSCAD/EMTDC. Flicker emission of this system is investigated. Reactive power compensation is mostly adopted for flicker mitigation. However, the flicker mitigation technique shows its limits, when the grid impedance angle is low in some distribution networks. A new method of flicker mitigation by controlling active power is proposed. It smoothes the 3p active power oscillations from wind shear and tower shadow effects of the wind turbine by varying the dc-link voltage of the full-scale converter. Simulation results show that damping the 3p active power oscillation by using the flicker mitigation controller is an effective means for flicker mitigation of variable-speed wind turbines with full-scale back-to-back power converters during continuous operation.

Flicker Mitigation by Active Power Control of Variable-Speed Wind Turbines With Full-Scale Back-to-Back Power Converters

A novel current-detection algorithm based on the time-domain approach for three-phase shunt active power filters (APFs) to eliminate harmonics, and/or correct power factor, and/or balance asymmetrical loads is analyzed in this paper. A basic overview and evaluation of the performance of existing current-detection algorithms for active power filters are presented. According to different complicated power quality issues and various compensation purposes, a novel current-detection algorithm is then proposed. Comparing with existing algorithms, this algorithm has shorter response time delay and clearer physical meaning. Different compensating current references can, thus, be accurately and easily obtained by adopting the proposed algorithm. It ensures that the shunt APF can very well achieve different compensation purposes. Moreover, it is very easy to implement this algorithm in a digital signal processor (DSP). Simulation results obtained with MATLAB and testing results on an experimental shunt APF are presented to validate the proposed algorithm.

A novel time-domain current-detection algorithm for shunt active power filters

In the wind energy conversion system, the wind turbine captures the wind energy Then the generator changes it to the electrical power So the characteristic of the wind turbine is very important For some laboratories that donpsilat have the practical wind turbine, it is very convenience to use the wind turbine simulator instead of the real wind turbine The paper introduces the structure and characteristic of the wind turbine simulator for Wind energy conversion systems using a permanent magnet synchronous motor (PMSM) The wind turbine simulator consists of a microcontroller, an intelligent power module (IPM) inverter, a PMSM and a control desk on the computer The control desk obtains the wind speed and calculates the theoretical torque of a real wind turbine by using the wind turbine characteristics and the rotation speed of PMSM Then the output torque of the PMSM can be regulated by controlling the stator current and frequency Hence, the inverter driven PMSM can work like a real wind turbine In this paper, torque oscillation produced by tower shadow and the wind shear has been considered Simulation results verify the analysis and the conclusion

Development of wind turbine simulator for wind energy conversion systems based on permanent magnet synchronous motor

Because of energy shortage and environment pollution, the renewable energy, especially wind energy has become more and more considerable all over the world. Direct drive wind energy conversion systems based on multipole permanent magnet synchronous generator (PMSG) have some advantages such as no gearbox, high power density, high precision and easy to control. In our research project, a 2MW direct drive wind energy conversion system is developed. In this paper, an efficient experimental method for high power converter is presented. A large circulating current flows in the converter, but only a small part of the current caused by the losses of the converter flows into the grid. The method can save a lot of energy when the converter is tested and the experiment can be done in the micro grid. The method can test the main stage, drive circuit, protect circuit and some parts of control circuit. Modeling and control scheme of the efficient experimental method are introduced in this paper, as well as the control scheme of the grid side converter. Some differences caused by sinusoidal pulse width modulation (SPWM) and space vector modulation (SVM) in the method have been analyzed. Simulation and experimental results verify the analysis and the conclusion.

An efficient experimental method for high power direct drive wind energy conversion systems

For 4 wire VSI, Under unbalanced grid voltage conditions, neutral currents that flow through the fourth wire will distort the symmetrical output voltage. And dc link voltage ripple will be produced. We introduced a three reference frame scheme to eliminate the dc link voltage ripple and output voltage distortion. Unbalanced grid voltage and ac link current are decomposed into positive, negative and zero sequence components. Positive sequence components is regulated in a positive synchronous reference frame (SRF), negative sequence components is regulated in a negative SRF, and zero sequence components is regulated in a zero SRF. In positive SRF, positive components appear as dc, while negative components appear as 2? rad/s. In contrast, in negative SRF, negative components appear as dc, while positive sequence appear as 2? rad/s. Zero sequence composents will not have any impace on dq, it appears as a disturbance in the o-variable at the fundamental frequency. In order to eleminated the dc link voltage ripple and output voltage distortion, positive, negative and zero sequence components shoud be controlled simultaneously. Simulation and experimental results are presented to verify the validity of the proposed control scheme.

Zhaoan Wang

Papers

Flicker Mitigation by Active Power Control of Variable-Speed Wind Turbines With Full-Scale Back-to-Back Power Converters

A novel time-domain current-detection algorithm for shunt active power filters

Development of wind turbine simulator for wind energy conversion systems based on permanent magnet synchronous motor

An efficient experimental method for high power direct drive wind energy conversion systems

Three Reference Frame Control Scheme of 4 wire Grid-connected Inverter for Micro Grid Under Unbalanced Grid Voltage Conditions