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

In this paper, a Distribution STATic COMpensator (DSTATCOM) is proposed for compensation of reactive power and unbalance caused by various loads in distribution system. An evaluation of three different methods is made to derive reference currents for a DSTATCOM. These methods are an instantaneous reactive power theory, a synchronous reference frame theory, and a new Adaline-based algorithm. The Adaline-based algorithm is an adaptive method for extracting reference current signals. These schemes are simulated under MATLAB environment using SIMULINK and PSB toolboxes. Simulation and experimental results demonstrate the performance of these schemes for the control of DSTATCOM.

A Comparison of Control Algorithms for DSTATCOM

This paper presents a nonlinear control technique for a three-phase shunt active power filter (SAPF). The method provides compensation for reactive, unbalanced, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently nonlinear SAPF system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the SAPF output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that significantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the SAPF reference currents, is proposed. The first step is to extract the SAPF reference currents from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase diode bridge rectifier with R-L load is taken as the nonlinear load, and then, the reference currents are modified, so that the delay will be compensated. The converter, which is controlled by the described control strategy, guarantees balanced overall supply currents, unity displacement power factor, and reduced harmonic load currents in the common coupling point. Various simulation and experimental results demonstrate the high performance of the nonlinear controller.

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

The objective of this paper is to propose a new inverter topology for a multilevel voltage output. This topology is designed based on a switched capacitor (SC) technique, and the number of output levels is determined by the number of SC cells. Only one dc voltage source is needed, and the problem of capacitor voltage balancing is avoided as well. This structure is not only very simple and easy to be extended to a higher level, but also its gate driver circuits are simplified because the number of active switches is reduced. The operational principle of this inverter and the targeted modulation strategies are presented, and power losses are investigated. Finally, the performance of the proposed multilevel inverter is evaluated with the experimental results of an 11-level prototype inverter.

A step-up switched-capacitor multilevel inverter with self-voltage balancing

Multilevel inverters (MLIs) are being used in wide range of power electronic applications. These converters have attracted a lot of attention during recent years and exist in different topologies with similar basic concepts. This paper presents five main submodules (SMs) to be used as the basic structures of MLIs. The paper reviews the common MLI topologies from the structural point of view. The topologies are divided into the different SMs to show conventional MLI configurations and future topologies that can be created from the main SMs. A comparative study between different topologies is performed in detail. The MLIs are categorized and investigated with from different perspectives such as the number of components, the ability to create inherent negative voltage, working in regeneration mode and using single dc source.

A General Review of Multilevel Inverters Based on Main Submodules: Structural Point of View

An active power compensator (APC) based on single-phase back-to-back power converter is proposed in this paper to solve problems of power quality of electric railway power supply system. This system adopts a single-phase feeding connection, which is called cophase power supply scheme. In this scheme, APC connects the balance transformer between feeding phase for power supply and another phase for compensation. It has some characteristics, such as active power balancing, reactive power compensating, and harmonics filtering. In order to achieve these characteristics, the control scheme requires seven combination models. In this paper, a multifunctional control algorithm is proposed to realize every conceivable model. A cophase system with APC based on field programmable gate array (FPGA) and YNvd balance transformer is also designed and evaluated. The experimental results obtained from this prototype illustrate that the compensating ability is extremely high in steady-state and dynamic responses, and the power quality of a substation with distorted loads can be improved integrally.

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

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

In this paper, a space vector pulsewidth modulation (PWM) (SVPWM) algorithm is proposed, which is in α'β' frame with dc-link capacitor voltage equalization for diode-clamped multilevel converters (DCMCs). The α'β' frame is a coordinate system similar to the αβ frame. In this frame, some original complex calculations are substituted by integer additions, integer subtractions, truncations, etc. It brings the time and area efficiency to fixed-point digital realization, particularly for the application in a field-programmable gate array. Meanwhile, a minimum energy property of multiple dc-link capacitors is applied as the basic principle for voltage equalization based on a capacitor current prediction algorithm. By evaluating the redundant vectors in each pulse dwelling period, the balancing algorithm chooses an optimal vector, generates the optimal PWM signals, and sustains the voltage stability. After that, an arbitrary multilevel SVPWM intellectual property core is designed and analyzed in the α'β' frame. At the end of this paper, a five-level DCMC-based static synchronous compensator is built and tested. The experimental results verify the balancing algorithm and the system steady-state and dynamic performances.

Multilevel SVPWM With DC-Link Capacitor Voltage Balancing Control for Diode-Clamped Multilevel Converter Based STATCOM

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies.

Voltage Balancing Approaches for Diode-Clamped Multilevel Converters Using Auxiliary Capacitor-Based Circuits

An advanced cophase traction power supply system is proposed to solve the power quality problems of the traditional traction power supply system, such as unbalance, reactive power, and harmonics to three-phase industrial grid. The three-phase to single-phase converter-based substation is adopted in this system, which can transfer active power from three-phase grid to single-phase catenary and compensate reactive power and harmonics of the locomotives. One catenary section could be utilized in the advanced cophase system instead of the multiple split sections in traditional system. The neutral sections and problems caused by them in traditional system could be avoided. In this paper, the characteristics of the advanced cophase system and the automatic current-sharing control algorithm of three-phase to single-phase converter are studied and analyzed. The simulation and experimental results verify the viability and effectiveness of the proposed system.

Zeliang Shu

Papers

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

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

Multilevel SVPWM With DC-Link Capacitor Voltage Balancing Control for Diode-Clamped Multilevel Converter Based STATCOM

Voltage Balancing Approaches for Diode-Clamped Multilevel Converters Using Auxiliary Capacitor-Based Circuits

Advanced Cophase Traction Power Supply System Based on Three-Phase to Single-Phase Converter