Digital Application of Second Order Generalized Integrator Based Grid Estimator Under Unbalanced and Distorted Voltage Conditions

Abstract

Frequency, amplitude, and phase information of the grid voltage are the main constraints for constructing a robust controller algorithm for grid connected applications under unbalanced and distorted voltage conditions. This paper narrates a simple, robust, straight forward method to estimate the instantaneous positive and negative sequence voltage components under unbalanced and distorted voltage circumstances. A second order generalized integrator (SOGI) is encapsulated to filter out the distorted voltage as well as to generate orthogonal voltage components for the three phases of AC grid. Furthermore, these filtered and orthogonal components are accounted for the calculation of instantaneous symmetrical components. Developed technique is more frequency adaptive compared to conventional phase locked loop (PLL) techniques. A set of test outcome results are provided in this paper based on MATLAB/Simulink simulations with real grid data captured from an industrial plant. Moreover, SOGI based estimator is digitally implemented by using dSPACE ds1103 digital controller to validate the numerical simulation results in accordance with the developed theoretical prediction.     

Small Wind Energy Systems

Abstract

The application of small wind turbines for residential and commercial applications depends on how a microgrid can operate in a suitable way. Because there is variable demand and a random nature of wind resources, it is usually necessary the installation of controllable end-use loads, storage devices, and a centralized distribution control. In order to establish a small wind energy system it is important to observe the following: (i) Attending the energy requirements of the actual or future consumers; (ii) Establishing civil liabilities in case of accidents and financial losses due to shortage or low quality of energy; (iii) Negotiating collective conditions to interconnect the microgrid with the public network or with other sources of energy that is independent of wind resources; (iv) Establishing a performance criteria of power quality and reliability to end-users, in order to reduce costs and guaranteeing an acceptable energy supply. This paper discuss how performance is affected by local conditions and random nature of the wind, power demand profiles, turbine related factors, and presents the technical issues for implementing a self-excited induction generator system, or a permanent magnet based wind turbine control, in addition of discussing the use of Magnus effect wind turbines for small scale generation.     

Determination of mechanical resonances in induction motors byrandom modulation and acoustic measurement

Acoustic noise emission from PWM-VSI inverter driven induction motors is a well-known problem. The generated noise depends mainly on two factors: the harmonic content of the supply voltage waveform; and the mechanical resonance frequencies of the induction motor. It is necessary to know the mechanical resonances to optimize the switching scheme of the inverter to reduce the noise emission. Measuring the resonance frequencies is normally a laborious process. This paper introduces a new method for estimating the mechanical resonances from acoustic noise measurements. Employing random modulation of the output voltage of the inverter, the voltage spectrum can be spread over a wide frequency range. Using the spectrum analysis of the measured acoustic noise, the resonances can easily be estimated as the dominant frequencies of the acoustic noise spectrum. The method was tested on a 2.2 kW induction motor at no load and full load. Some of the mechanical resonances of the motor at no load were calculated by the Holzer method. The calculations showed good agreement with the sound measurements. The influence of the fan cowl was investigated and it is concluded that this is an important factor in the acoustic noise emission. Finally, it was observed that new mechanical resonances appeared when the induction motor was loaded by a pump drive system, and they were estimated by the measurement technique     

Wind turbine Generator modeling and Simulation where rotational speed is the controlled variable

To optimize the power produced in a wind turbine, the speed of the turbine should vary with the wind speed. A simple control method is proposed that will allow an induction machine to run a turbine at its maximum power coefficient. Various types of power control strategies have been suggested for application in variable speed wind turbines. The usual strategy is to control the power or the torque acting on the wind turbine shafts. This paper presents an alternative control strategy, where the rotational speed is the controlled variable. The paper describes a model, which is being developed to simulate the interaction between a wind turbine and the power system. The model is intended to simulate the behavior of the wind turbine using induction generators both during transient grid fault events and during normal operation. Sample simulation results for two induction generators (2/0.5 MW) validate the fundamental issues.     

矩阵变换器的建模与仿真

该文着重讨论矩阵变换器的建模与仿真。文中给出了矩阵变换器的两种模型：基于间接空间矢量调制法的模型和基于功率守恒方程的模型，详细介绍了这两种模型建立的理论基础和建立过程，并结合这两种模型在研究不同问题时的仿真结果，说明模型难有绝对的好坏之分，应针对不同的问题采用不同的模型。文中同时也介绍了矩阵变换器建模中应注意的问题及技巧，为深入进行矩阵变换器的仿真研究提供了参考和借鉴。     

BEGA-a biaxial excitation Generator for automobiles: comprehensive characterization and test results

This paper presents the design and test results for a biaxial excitation generator/motor for automobiles (BEGA), which has a three-phase stator and a salient-pole excited heteropolar rotor with multiple flux barriers filled with low-cost permanent magnets (PMs). For this new generator, the low-voltage regulation is obtained by the flux-barrier PM combination with field (excitation) low-power control and a full-power diode rectifier in the stator. Good power/volume and superior efficiency (up to 80%) are obtained at costs comparable to those of an existing Lundell generator. The generator configuration, principle, equations, finite-element field analysis, design optimization, performance characteristics, and test results, together with the generating system simulations, constitute the core of the paper.     

Multi-Timescale Modeling and Dynamic Stability Analysis for Sustainable Microgrids: State-of-the-Art and Perspectives

The increasing trend for integrating renewable energy sources into the grid to achieve a cleaner energy system is one of the main reasons for the development of sustainable microgrid (MG) technologies. As typical power-electronized power systems, MGs make extensive use of power electronics converters, which are highly controllable and flexible but lead to a profound impact on the dynamic performance of the whole system. Compared with traditional large-capacity power systems, MGs are less resistant to perturbations, and various dynamic variables are coupled with each other on multiple timescales, resulting in a more complex system in-stability mechanism. To meet the technical and economic challenges, such as active and reactive power-sharing, volt-age, and frequency deviations, and imbalances between power supply and demand, the concept of hierarchical control has been introduced into MGs, allowing systems to control and manage the high capacity of renewable energy sources and loads. However, as the capacity and scale of the MG system increase, along with a multi-timescale control loop design, the multi-timescale interactions in the system may become more significant, posing a serious threat to its safe and stable operation. To investigate the multi-timescale behaviors and instability mechanisms under dynamic inter-actions for AC MGs, existing coordinated control strategies are discussed, and the dynamic stability of the system is defined and classified in this paper. Then, the modeling and assessment methods for the stability analysis of multi-timescale systems are also summarized. Finally, an outlook and discussion of future research directions for AC MGs are also presented.     

An integral space-vector PWM technique for DSP-controlledvoltage-source inverters

A novel pulsewidth modulation (PWM) technique for voltage-source inverters, based on the idea of space vectors of switching integrals is presented. In contrast to most existing PWM methods, no explicit timing is required, smooth transition from the PWM mode to the square-wave mode is ensured, and minimum allowable widths of pulses and notches are guaranteed. The control algorithm is conceptually simple and easily implementable in a digital signal processor. Four parameters of the modulation strategy are adjustable, allowing tuning of the modulator to requirements imposed by the application. Voltage spectra have a low harmonic content, most of the power being dispersed as the continuous power density. A prototype modulator is described and illustrated by the results of laboratory experiments     

Combined Flux Observer With Signal Injection Enhancement for Wide Speed Range Sensorless Direct Torque Control of IPMSM Drives

This paper proposes a motion-sensorless control system using direct torque control with space vector modulation for interior permanent magnet synchronous motor (IPMSM) drives, for wide speed range operation, including standstill. A novel stator flux observer with variable structure uses a combined voltage-current model with PI compensator for low-speed operations. As speed increases, the observer switches gradually to a PI compensated closed-loop voltage model, which is solely used at high speeds. High-frequency rotating-voltage injection with a single D-module bandpass vector filter and a phase-locked loop state observer with a new synchronization procedure are used to estimate the rotor position, which is needed only by the current model in stator flux observer at low speeds. A new rotor speed estimator for the whole speed-loop range, based on the stator flux speed estimation with a new dynamic correction depending on estimated torque, is proposed and tested. Extensive simulation results and significant experimental results provided good performance for the proposed IPMSM sensorless system in more than 1:1000 speed range, under full-load operation, from very low speeds (1 r/min experimental) up to rated speed.