M.E. Haque

A Novel Control Strategy for a Variable Speed Wind Turbine with a Permanent Magnet Synchronous Generator

This paper presents a novel control strategy for the operation of a direct drive permanent magnet synchronous generator (PMSG) based stand alone variable speed wind turbine. The control strategy for the generator side converter with maximum power extraction is discussed. The stand alone control is featured with output voltage and frequency controller capable of handling variable load. The potential excess of power is dissipated in the damp resistor with the chopper control and the dc link voltage is maintained. Dynamic representation of dc bus and small signal analysis are presented. Simulation results show that the controllers can extract maximum power and regulate the voltage and frequency under varying wind and load conditions. The controller shows very good dynamic and steady state performance.

A direct torque-controlled interior permanent-magnet synchronous motor drive without a speed sensor

This paper reports results of further investigation of the so-called direct torque control (DTC) technique to an interior permanent magnet (1PM) synchronous motor drive. This torque control technique for IPM motors requires no dq-axes current controllers and coordinate transformnation networks. A completely sensorless 1PM motor drive with DTC, which uses a new speed estimator from the stator flux linkage vector and the torque angle, is presented. It is shown that including the torque angle in the estimation process results in a far more accurate transient speed estimator than what is reported in the existing literature.

Problems associated with the direct torque control of an interior permanent-magnet synchronous motor drive and their remedies

This paper investigates problems associated with the implementation of a direct torque control (DTC) strategy for an interior permanent-magnet synchronous motor drive. The DTC technique is increasingly drawing attention because of elimination of current controllers and, hence, their inherent delays, and elimination of the rotor position sensor. The latter advantage perhaps is the main impetus for considering this new approach of torque control. Problems associated with this controller, namely, the offset in the current measurements, the stator resistance variation, and the requirement of initial rotor position are addressed in this paper. Ways of mitigating of these problems are also investigated in this paper. These are evaluated with modeling and experimental studies, results of which are also presented.

Control of a stand alone variable speed wind turbine with a permanent magnet synchronous generator

A novel control strategy for the operation of a permanent magnet synchronous generator (PMSG) based stand alone variable speed wind turbine is presented in this paper. The direct drive PMSG is connected to the load through a switch mode rectifier and a vector controlled pulse width modulated (PWM) IGBT-inverter. The generator side switch mode rectifier is controlled to achieve maximum power from the wind. The load side PWM inverter is using a relatively complex vector control scheme to control the amplitude and frequency of the inverter output voltage. As there is no grid in a stand-alone system, the output voltage has to be controlled in terms of amplitude and frequency. The stand alone control is featured with output voltage and frequency controller capable of handling variable load. A damp resistor controller is used to dissipate excess power during fault or over-generation. The potential excess of power will be dissipated in the damp resistor with the chopper control and the dc link voltage will be maintained. Extensive simulations have been performed using Matlab/Simpower. Simulation results show that the controllers can extract maximum power and regulate the voltage and frequency under varying load condition. The controller performs very well during dynamic and steady state condition.

A Novel Operation and Control Strategy for a Standalone Hybrid Renewable Power System

This paper proposes a novel operation and control strategy for a renewable hybrid power system for a standalone operation. The proposed hybrid system consists of a wind turbine, a fuel cell, an electrolyzer, a battery storage unit, and a set of loads. The overall control strategy is based on a two-level structure. The top level is the energy management and power regulation system. Depending on wind and load conditions, this system generates reference dynamic operating points to low level individual subsystems. The energy management and power regulation system also controls the load scheduling operation during unfavorable wind conditions under inadequate energy storage in order to avoid a system blackout. Based on the reference dynamic operating points of the individual subsystems, the local controllers control the wind turbine, fuel cell, electrolyzer, and battery storage units. The proposed control system is implemented in MATLAB Simpower software and tested for various wind and load conditions. Results are presented and discussed.

Dynamic operation and control of a hybrid wind-diesel stand alone power systems

This paper presents the dynamic operation and control strategies of a hybrid wind-diesel-battery energy storage based power supply system for isolated communities are investigated. Control strategies for voltage and frequency stabilization and efficient power flow among the hybrid system components are developed. The voltage and frequency of the hybrid wind-diesel system is controlled either by a load side inverter or by diesel generation depending on the wind conditions. During high penetration of wind, the wind turbine supplies the required power to the load. A battery energy storage system is connected to the dc-link to balance the power generated from the wind turbine and the power demand by load. Under low wind conditions, a diesel generator is used with wind energy conversion system to generate the required power to the load. A power sharing technique is developed to allocate power generation for diesel generator in low wind conditions. Results show that the control strategies work very well under dynamic and steady state condition to supply power to the load.

A Simulated Annealing Global Maximum Power Point Tracking Approach for PV Modules Under Partial Shading Conditions

This paper proposes a simulated annealing (SA)-based global maximum power point tracking (GMPPT) technique designed for photovoltaic (PV) systems which experience partial shading conditions (PSC). The proposed technique is compared with the common perturb and observe MPPT technique and the particle swarm optimization method for GMPPT. The performance is assessed by considering the time taken to converge and the number of sample cases where the technique converges to the GMPP. Simulation results indicate the improved performance of the SA-based GMPPT algorithm, with arbitrarily selected parameters, in tracking to the global maxima in a multiple module PV system which experiences PSC. Experimental validation of the technique is presented based on PV modules that experience nonuniform environmental conditions. Additionally, studies regarding the influence of the key parameters of the SA-based algorithm are described. Simulation and experimental results verify the effectiveness of the proposed GMPPT method.

Influence of stator resistance variation on direct torque controlled interior permanent magnet synchronous motor drive performance and its compensation

This paper addresses the problem of the variation of stator resistance, which significantly degrades the performance of a direct torque controlled (DTC) interior permanent magnet (IMP) synchronous motor. The problem is manifested by errors in the estimated flux linkage vector and in the electromagnetic torque, which causes unstable operation of the DTC drive. The extent of the problem associated with variation of stator resistance on the performance of the DTC controller of an interior permanent magnet synchronous motor drive is first presented, followed by a technique for the estimation and compensation of the effect of stator resistance variation. A method of stator resistance estimation using proportional-integral (PI) estimator has been investigated in this paper. Modeling and experimental results presented clearly demonstrate the effectiveness of the estimator in tracking the stator resistance and in compensating for the effects of its variation.

Grid integration impacts and energy storage systems for wind energy applications — A review

Grid integration of variable wind power is confronted with many challenges. Challenges and issues associated with large scale wind integration into the existing power grid are discussed in this paper. Different wind turbine technologies and their technical features are presented. A review of the state of the art energy storage technologies, their characteristic features and comparison are presented. Finally, application of a hybrid battery-supercapacitor based energy storage systems with a direct drive variable speed wind turbine is investigated and simulation results are presented.

Review of Maximum Power Point Tracking approaches suitable for PV systems under Partial Shading Conditions

Maximum Power Point Tracking (MPPT) is an important consideration in Photovoltaic (PV) Systems, particularly as these systems increase in size and are exposed to non-uniform environmental conditions. Conventional MPPT techniques are designed to track the Maximum Power Point under uniform conditions where there is a single maximum power. Under non-uniform environmental conditions, with bypass diodes integrated into the circuit, the Power-Voltage characteristics become more complex resulting in multiple local maxima. Under such conditions, conventional MPPT techniques cannot track the global maxima and may result in considerable energy losses. This review paper explores the approaches designed to mitigate the complexities arising from non-uniform environmental conditions in PV system operation.