This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

High-Power Wind Energy Conversion Systems: State-of-the-Art and Emerging Technologies

The main objective of this two-part state-of-the-art paper called “Recent Advances in the Design, Modeling, and Control of Multiphase Machines” is to present latest contributions in the multiphase machines' field. The first part of this paper focuses on the recent progress in the design, modeling, and control, whereas the drive is in healthy operation. This second part presents relevant contributions in two not analyzed fields. The first is in relation with the use of the additional degrees of freedom of multiphase machines and the exploitation of their fault-tolerant capabilities without adding extra hardware. The second one analyzes multiphase generation, particularly in grid-connected wind energy conversion systems and stand-alone applications. Recent progresses are shown and open challenges and future research directions are discussed.

Recent Advances in the Design, Modeling, and Control of Multiphase Machines—Part II

In this paper, a new medium voltage power converter topology using a diode rectifier, three-level boost (TLB) converter, and neutral-point-clamped (NPC) inverter is proposed for a high-power permanent magnet synchronous generator-based wind energy conversion system. The generator-side TLB converter performs the maximum power point tracking and balancing of dc-link capacitor voltages, while the grid-side NPC inverter regulates the net dc-bus voltage and reactive power to the grid. A significant improvement in the grid power quality is accomplished as the NPC inverter no longer controls the dc-link neutral point voltage. A model predictive strategy is proposed to control the complete system where the discrete-time models of the proposed power electronic converters are used to predict the future behavior of control variables. These predictions are evaluated using two independent cost functions, and the switching states which minimize these cost functions are selected and applied to the generator- and grid-side converters directly. In order to comply with the high-power application, the switching frequencies of the TLB converter and NPC inverter are minimized and maintained below 1.5 and 1 kHz, respectively. The proposed topology and control strategy are verified through MATLAB simulations on a 3-MW/3000-V/577-A system and dSPACE DS1103-based experiments on 3.6-kW/208-V/10-A prototype.

Predictive Control of a Three-Level Boost Converter and an NPC Inverter for High-Power PMSG-Based Medium Voltage Wind Energy Conversion Systems

This paper presents an investigation of the finite-control-set model predictive control (FCS-MPC) of a five-phase induction motor drive. Specifically, performance with regard to different selections of inverter switching states is investigated. The motor is operated under rotor flux orientation, and both flux/torque producing (d-q) and nonflux/torque producing (x-y) currents are included into the quadratic cost function. The performance is evaluated on the basis of the primary plane, secondary plane, and phase (average) current ripples, across the full inverter's linear operating region under constant flux-torque operation. A secondary plane current ripple weighting factor is added in the cost function, and its impact on all the studied schemes is evaluated. Guidelines for the best switching state set and weighting factor selections are thus established. All the considerations are accompanied with both simulation and experimental results, which are further compared with the steady-state and transient performance of a proportional-integral pulsewidth modulation (PI-PWM)-based current control scheme. While a better transient performance is obtained with FCS-MPC, steady-state performance is always superior with PI-PWM control. It is argued that this is inevitable in multiphase drives in general, due to the existence of nonflux/torque producing current components.

/pdf/fcs-mpc-based-current-control-of-a-five-phase-induction-1xms1t9ik4.pdf

FCS-MPC-Based Current Control of a Five-Phase Induction Motor and its Comparison with PI-PWM Control

The low-voltage ride through (LVRT) requirement demands the wind power plants to remain connected to the grid in the presence of grid voltage dips, actively helping the network overall control to keep network voltage and frequency stable. Wind power technology points to increase power ratings. Hence, multilevel converters, as for example, neutral-point- clamped (NPC) converters, are well suited for this application. Predictive current control presents similar dynamic response and reference tracking than other well-established control methods, but working at lower switching frequencies. In this paper, the predictive current control is applied to the grid-side NPC converter as part of a wind energy conversion system, in order to fulfill the LVRT requirements. DC-link neutral-point balance is also achieved by means of the predictive control algorithm, which considers the redundant switching states of the NPC converter. Simulation and experimental results confirm the validity of the proposed control approach.

/pdf/model-predictive-current-control-of-grid-connected-neutral-1du6qa8tj5.pdf

Model Predictive Current Control of Grid-Connected Neutral-Point-Clamped Converters to Meet Low-Voltage Ride-Through Requirements

The development of wind energy conversion systems (WECS) is currently focused in reaching higher power ratings (≈10MW). Medium voltage operation is at this power level, particularly at grid side, a desirable feature. Therefore, great attention has been given to high-power medium-voltage multilevel converters for WECS. Nevertheless, most modern multi-megawatt turbines use low-voltage multiphase permanent magnet synchronous generators (PMSG) operating at 690V, which requires the use of several converters connected in parallel to reach the multi-megawatt level. This paper presents a low- to medium-voltage converter interface for a dual three-phase PMSG based WECS. Two full bridge diode rectifiers followed by boost converters are used to control each set of three-phase windings of the dual PMSG. The boost converters elevate the voltage to feed each one of the capacitors of the dc-link of the medium voltage NPC grid-tied inverter. The generator side converter has high power density and is a cost effective solution compared to traditional back-to-back solutions. Simulation results are presented to provide a preliminary overview of the performance of the system.

Dual-boost-NPC converter for a dual three-phase PMSG wind energy conversion system

In order to improve the performance at steady state of a three-phase drive system, numerous works have been focused in reducing the current and torque ripple. Predictive current control allows the improvement of the performance by increasing the sampling frequency, but the resulting switching frequency can generate semiconductors operating point out of their thermal limits. The ripple of current using conventional linear current control with pulse width modulation is reduced by increasing the carrier frequency, however, the upper limit of the switching frequency is limited also by the semiconductors thermal rates. In this paper a predictive current control modification is proposed for reducing the switching frequency by decoupling it from the sampling time, thus the performance of the system is improved but the switching frequency is kept bellow its limits. A comparison between the proposed method and linear current control with PWM of a three phase voltage source inverter operating at steady state is presented.

Predictive current control with reduction of switching frequency for three phase voltage source inverters

Conventional linear current control with pulse width modulation and predictive current control for a three phase voltage source inverter are compared in this paper based on the ripple of current for a range of switching frequencies. Predictive current control allows to improve the performance by increasing the sampling frequency, but the resulting switching frequency can also make the semiconductors to operate out of their thermal limits. Behavior of the predictive control scheme for a range of switching frequencies is presented. A modification of the predictive current control is presented for decoupling the switching frequency from the sampling frequency, thus the performance of the system is improved and the switching frequency is kept controlled.

http://ieeexplore.ieee.org/iel5/6014782/6020091/06020641.pdf

A comparative study of predictive current control for three-phase voltage source inverters based on switching frequency and current error

Commercial wind turbines have increased in size and power in the last decade, reaching 7.5MW. This has driven the development of new converter-generator wind turbine configurations where permanent magnet synchronous generators (PMSG) have been at the forefront due to the higher power density, efficiency and lower maintenance, compared to the classic doubly fed induction generator (DFIG). In this paper a new WECS configuration is explored based on an open-end winding three-phase PMSG. The proposed converter configuration allows to elevate the low voltage at generator side to a medium-voltage at the grid side. Each three-phase terminal of the machine is connected to a full bridge diode rectifier, followed by a dc-dc boost converter to elevate the voltage level and control the MPPT. The grid side converter is a three-level neutral point clamped (NPC) inverter operating at medium-voltage level. The performance of the proposed configuration is verified by simulation using PSIM and MatLab & Simulink platforms.

Open-end-winding PMSG for wind energy conversion system with dual boost NPC converter

This work proposes the application of model predictive control (MPC) to the control of five-phase voltage source inverters The additional switching states and degrees of freedom present in multiphase inverters increase the number of calculations in the predictive control algorithm making difficult to implement optimization problem online In this paper a method to reduce the calculations is proposed MPC prove to maintain the same simplicity and effectiveness as for three-phase converters The successful performance of the proposed method of control for five-phase converters is verified by simulation

Luna Vattuone

Papers

Dual-boost-NPC converter for a dual three-phase PMSG wind energy conversion system

Predictive current control with reduction of switching frequency for three phase voltage source inverters

A comparative study of predictive current control for three-phase voltage source inverters based on switching frequency and current error

Open-end-winding PMSG for wind energy conversion system with dual boost NPC converter

A method of predictive current control with reduced number of calculations for five-phase voltage source inverters