Parallel Operation of Permanent Magnet Generators in Autonomous Wind Energy Conversion System

This paper deals with an isolated wind-hydro hybrid generation system employing a Squirrel Cage Induction Generator (SCIG) driven by hydro turbine and a Permanent Magnet Synchronous Generator (PMSG) driven by a variable speed wind turbine feeding three-phase four-wire local loads. The proposed system utilizes two back to back connected Pulse Width Modulated (PWM) Insulated Gate Bipolar Transistors (IGBTs) based voltage source converters (VSCs) with a battery energy storage system (BESS) at their dc link. The main objectives of the control algorithm for VSCs are to achieve maximum power tracking (MPT) through rotor speed control of wind turbine driven PMSG under varying wind speeds, and control of the magnitude and the frequency of the load voltage. The proposed wind hydro hybrid system is having capability of bidirectional active and reactive powers flow, by which it controls the magnitude and the frequency of the load voltage. The proposed electro-mechanical system using PMSG and SCIG, a MPT controller and a voltage and frequency controller (VFC) are modeled and simulated in MATLAB using Simulink and Sim Power System (SPS) set toolboxes and different aspects of the proposed system are studied for various types of linear loads and nonlinear loads and under varying wind speed conditions. The performance of the proposed system is presented to demonstrate its capability of MPT, VFC, harmonic elimination and load balancing.

This paper deals with an application of the power balance theory in a voltage and frequency controller (VFC) of an autonomous wind power generation using an isolated asynchronous generator (IAG) feeding three-phase four wire loads. The reference generator currents are estimated using the power balance theory to control the voltage and frequency of IAG system. Three-leg voltage source converter (VSC) with a battery energy storage system (BESS) is used as a VFC for the power management of the wind energy conversion system (WECS). Bi-directional power flow capabilities of the proposed VFC in WECS are demonstrated through simulation results. The proposed VFC works as an IAG exciter, a voltage regulator, a load leveler, a load balancer and a harmonic eliminator in the WECS. The wind power driven IAG system is modeled and simulated in the MATLAB using the Simulink and the sim power system (SPS) toolboxes.

This paper deals with a new control algorithm for a voltage and frequency controller (VFC) of an isolated wind energy conversion system (IWECS) using an isolated asynchronous generator to feed three-phase four-wire consumer loads. The reference source currents are estimated for the indirect current control of a voltage source converter (VSC) using the single-phase PQ theory to control the voltage and frequency of IWECS. A three-leg VSC with a battery energy storage system is used as a VFC for an IWECS. A nonisolated star-polygon transformer is used to provide a neutral terminal for four-wire loads and to compensate the neutral current resulting in reduction in rating of VSC. The proposed VFC is implemented using a DSP. Experimental results are presented to demonstrate the additional capabilities of VFC as a load leveler, a load balancer, a harmonic eliminator, and a neutral current compensator.

This work deals with the operation and control of a wind turbine driven isolated asynchronous generator (IAG) system to feed three-phase four-wire consumer loads. The voltage and frequency controller (VFC) of IAG consists of a three-leg voltage sourced converter (VSC) and a battery energy storage system. A zig-zag transformer is used to provide the neutral terminal for three-phase four wire consumer loads and to reduce the rating of the VSC. An instantaneous reactive power theory (IRPT) is implemented for the derivation of reference source currents using a DSP. The performance of VFC of IAG is demonstrated through extensive test results.

This paper proposes an improved-second order generalized integrator (SOGI) based decoupled voltage and frequency controller (DVFC) for permanent magnet synchronous generator (PMSG) based pico-hydro system with power quality improvement. The proposed pico-hydro system consists of a voltage source converter (VSC) used for harmonics mitigation, regulating voltage at point of common coupling (PCC), and DC-link voltage control. The decoupled frequency controller consists of a conventional electronic load controller (ELC) using uncontrolled three-phase diode bridge rectifier along with an insulated gate bi-polar transistor (IGBT) switch-based DC-DC converter connected in series to an auxiliary load. The frequency is regulated by dumping excess energy into the auxiliary load. The VSC and decoupled ELC, are connected in parallel to the load. The improved-second order generalized integrator (SOGI) based control algorithm is used to generate switching pulses for the VSC. The addition of damping factors, provides faster convergence, good dynamic response and improves steady-state performance of the given system. The proposed ISOGI based control algorithm with decoupled frequency controller for PMSG, is validated on a laboratory prototype with experimental implementation.

This paper deals with a stand-alone single-phase power generation using a three-phase isolated asynchronous generator (IAG) coupled with a wind turbine or a pico-hydro turbine. The proposed voltage and frequency controller (VFC) for a stand-alone single-phase power generation is used as a phase balancer for a three-phase IAG, a load leveler, and an active filter. The VFC is realized using a three-leg voltage-source converter and a battery energy storage system. The VFC ensures optimum utilization of a three-phase IAG for feeding a variety of single-phase loads, improves conversion efficiency, and reduces noise and vibration in the IAG. The rating considerations of an IAG and VFCs are also discussed for a single-phase power generation. The performance of an IAG system is demonstrated under steady-state and dynamic conditions of feeding single-phase linear and nonlinear loads. Simulated results are validated with test results on a developed system.

This article focuses on improving the performance of the autonomous wind energy conversion system based on a Permanent Magnet Synchronous Generator (PMSG). There are several problems related to the control of this system, such as chattering phenomenon, static error and coupling between d-q currents, associated with the use of conventional regulators like the PI controller. To remedy these problems, a comparative study is performed between the Super Twisting Sliding Mode Controller (STSMC) and Adaptive Fuzzy Sliding Mode Controller (AFSMC) that are used to drive the rotor speed to the optimal speed to get the maximum power. The simulation study shows that the proposed STSMC is more effective at different operating conditions.

This study deals with an implementation of a constant speed permanent magnet synchronous generator (PMSG)-based three-phase stand-alone wind energy conversion system (SWECS). The voltage and frequency controller is realised using only a single voltage source converter (VSC) and a battery energy storage system (BESS). The BESS is used to provide load levelling under varying wind speeds and to control frequency of SWECS. The voltage of PMSG is regulated under varying wind speeds and loads by supplying the reactive power from VSC. The performance of SWECS is demonstrated as a load leveller, a load balancer, a harmonic compensator and a voltage and frequency controller.

This paper deals with the fuzzy logic based proportional-integral (FPI) regulators for voltage and frequency control (VFC) of an isolated asynchronous generator (IAG) in a wind energy conversion system (WECS). A three-leg voltage source converter (VSC) with battery supported energy storage (BSES) is used as a VFC. The VFC algorithm uses two fuzzy PI regulators, to improve the dynamic performance of the WECS. A three-phase four-wire WECS is realized in support with a zig-zag transformer connected at load bus. An extensive study is made based on performance of the controller to emphasize the merits of using FPI regulators in control algorithm. The proposed WECS is modeled and simulated in the MATLAB using simulink and sim power system toolboxes.

Presented herein is Uniform Input Voltage Distribution (UIVD) control [6–9] for Distributed-Input Series-Output (DISO) converter power systems. The primary control objective of UIVD for DISO converters is to achieve grouped maximum power throughput from non-identical renewable power sources. Secondly, this paper features a revised Maximum Power Tracking (MPT) controller design developed for DISO configurations that facilitate simultaneous processing of distributed power flows. In earlier research, the distributed source peak powers are individually tracked by converters controlled by independent MPT controllers without UIVD. However, when distributed power sources have similar peak power voltages with an achievable tracking efficiency of greater than 96%, such independent MPT controllers are not necessary. By utilizing UIVD control, near-maximum use of available power is achieved using a single MPT controller. The resulting system and control architectures offer near-maximum power transfer with a lower parts count. Two DISO power converter bus architectures are described herein: one having a battery-dominated output voltage and the other with a regulated output voltage. Through computer simulation, both power architectures are validated for fault-tolerant grouped UIVD control.

This paper evaluates an isolated system using a character of triangle function (CTF) based control methodology for control and improved power quality. The hybrid-isolated system consists of a solar photovoltaic (SPV) array, diesel driven permanent magnet synchronous generator (PMSG) and a battery energy storage system (BESS). The configuration of the controller is simple and it is employed for the estimation of the source reference currents. The essential objective of a four-leg voltage source converter (VSC) is to provide voltage control, load balancing, neutral current compensation and harmonics elimination while feeding three phase four wire loads. The performance of the system with proposed control strategy has been estimated by modelling the system in Matlab with Simulink and SPS (Sim-Power System) toolboxes and authenticated through simulation results.

Recently, offshore wind farms have emerged as the most promising sector in the global renewable energy industry. The main reasons for the rapid development of offshore wind farms includes much better wind resources and smaller environmental impact (e.g., audible noise and visual effect). However, the current state of the offshore wind power presents economic challenges significantly greater than onshore. In this thesis, a novel interconnecting method for permanent magnet synchronous generator (PMSG)-based offshore wind farm is proposed, where cascaded pulse-width modulated (PWM) current-source converters (CSCs) are employed on both generator- and grid-side. With the converters in cascade to achieve high operating voltages, the proposed method eliminates the need for bulky and very costly offshore converter substation which is usually employed in voltage source converter (VSC) high voltage DC (HVDC)-based counterparts. Related research in terms of control schemes and grid integration are carried out to adapt the proposed cascaded CSC-based offshore wind farm configuration. The large distance between generator- and grid-side CSC in the proposed wind farm configuration addresses significant challenges for the system control. In order to overcome the problem, a novel decoupled control scheme is developed. The active and reactive power control on the grid-side converters are achieved without any exchange of information from the generator-side controller. Therefore, the long distance communication links between the generator- and grid-side converters are eliminated and both controllers are completely decoupled. At the same time, the maximum power tracking control is achieved for the generator-side converters that enable full utilization of the wind energy. Considering inconsistent wind speed at each turbine, a coordinated control scheme is proposed for the cascaded CSC-based offshore wind farm. In proposed control strategy, the wind farm supervisory control (WFSC) is developed to generate the optimized dc-link current control. This enables all the turbines to independently track their own MPPT even with inconsistent wind speed at each turbine. Grid integration issues, especially the fault ride-through (FRT) capability for the cascaded CSC-based offshore wind farm are addressed. Challenges in implementing existing FRT methods to the proposed offshore wind farm are identified. Based on this, a new FRT strategy using inherent short circuit operating capability of the CSC is developed. Moreover, the mitigation strategy is developed to ensure the continuous operation of the cascaded CSC-based offshore wind farm when one or more turbines fail to operate. Simulation and experimental verification for various objectives are provided throughout the thesis. The results validate the proposed solutions for the main challenges of the cascaded current source converter based offshore wind farm.

A Novel Maximum Power Tracking by VSAS approach for Permanent Magnet Direct Drive WECS

With the advance of power electronics, direct-driven permanent magnet synchronous generators have drawn increased interest to wind turbine manufacturers due to its advantages over other variable-speed wind turbines. This article studies permanent magnet synchronous generator characteristics under the general d-q control strategy in the rotor-flux-oriented frame so as to benefit the development of advanced permanent magnet synchronous generator control technology. Compared to traditional approaches, the specific features of the article are (1) a steady-state permanent magnet synchronous generator model in a d-q reference frame, (2) a simulation mechanism that reflects the general permanent magnet synchronous generator d-q control strategy, (3) an integrative study that combines generator-converted power with extracted wind power characteristics, and (4) a joint investigation incorporating both steady-state and transient evaluations. Extensive simulation-based analysis is conducted to study how permanent magnet synchronous generator characteristics are affected by different d-q control conditions and are interacted with wind power drive characteristics in power generation and speed regulation of a permanent magnet synchronous generator wind turbine.

Cooperation of large-scale wind farm and battery storage in frequency control: An optimal Fuzzy-logic based controller