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This study focuses on a virtual synchronous machine (VSM) based on voltage source converters to mimic the behavior of synchronous machines (SMs) and improve the damping ratio of the power system. The VSM model is simplified according to some assumptions (neglecting the speed variation and the stator transients) to allow for the possibility of dealing with low-frequency oscillation in large-scale systems with many VSMs. Furthermore, a virtual power system stabilizer (VPSS) structure is proposed and tuned using a method based on a linearized power system dynamic model. The linear and nonlinear analyses examine the stability of two modified versions of a 16-machine power system in which, in the first case, partial classical machines are replaced by VSMs, and in the second case, all SMs are replaced by VSMs. The simulation results of the case studies validate the efficiency of the proposed control strategy.

In this paper, a composite control strategy for improved off-grid configuration based on photovoltaic (PV array), a wind turbine (WT), and a diesel engine (DE) generator to achieve high performance while supplying nonlinear loads is investigated. To operate the WT efficiently under variable speed conditions and to obtain accurate and fast convergence to the maximum global operating point without a speed sensor, an iterative interpolation method is integrated with the perturbation and observation (P&O) technique. To ensure the balance of power in the system and to achieve the maximum power from the PV array without using any maximum power point tracking (MPPT) method, and ensuring stable operation during the disturbance, a double-loop control strategy for a two-switches buck-boost converter is developed. Furthermore, to protect the synchronous generator of the diesel generator (DG) from the 5th and 7th order-harmonics created by the connected nonlinear loads and to solve the issue of the filter resonance, the interfacing three-phase inverter is controlled using an improved synchronous-reference frame algorithm (SRF) with virtual impedance active damping. The presented work demonstrates effective and efficient control along with improved performance and cost-effective option as compared to the similar works reported in the literature. The performance of the presented off-grid configuration and its developed composite control strategy are tested using MATLAB/Simulink and validated through small-scale hardware prototyping. [ABSTRACT FROM AUTHOR]

This article presents a potential wind energy conversion system (WECS) using the recently proposed brushless induction excited synchronous generator (BINSYG), which can operate as a self-excited synchronous-machine. In BINSYG, an induction-machine (IM) and a synchronous-machine (SM) are wound for different number of poles and are embedded in the same machine structure. By operating the SM in self-excited mode, dc-link voltage of grid-side inverter can be controlled smoothly from the stator side of the IM. A set of conditions has to be maintained for stable operation in self-excited mode. This is particularly critical when the machine needs to be operated in wide variation in speed. So far, no stability-study is available to explore the stable-operating-zone, when the machine operates in self-excited mode. Therefore, in this paper stability of self-excited BINSYG is investigated to check suitability of the proposed system for wind energy applications. The study clearly indicates the presence of a critical speed (i.e. a minimum speed below which self-excitation is not possible). The movement of eigen values are presented to show the influence of several parameters on stable behavior of the system. Simulations using PLECS and supporting experimental-results using a laboratory-prototype (configured for 4/6 poles, 5.5 kVA) have been presented. [ABSTRACT FROM AUTHOR]

This article deals with the problem H∞ control under network T-S fuzzy system with random packet dropouts for the synchronous machine. In the control design, the intermittent data loss existing in the closed-loop system is taken into account. Two main approaches adopted in this paper to design the fuzzy controller. First, a new version of the T-S fuzzy state-feedback controller is constructed to guarantee the resulting closed-loop system to be stochastically stable. Furthermore, in this regard, by taking into account a new version of fuzzy Lyapunov-Krasovskii functional (LKF) in conjunction with free weighting matrices, containing mode-dependent non-integral term such that the resulting system is stochastically stable with the desired performance. Second, to establish the pole place method (PPM) with the membership function. Furthermore, to make the controller design more convenient, the designed controller does not need to share the number of fuzzy rules and membership functions with the model. Synchronous machine parameters are used for the simulation results which are provided to show the usefulness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Dynamic operational behavior (DOB) of electrical machines can cause effects that are difficult to describe and understand. The short-circuit behavior (SCB) in particular is a dangerous DOB for machine and human. It could destroy the machine itself and cause heavy damage to the power supply unit and mechanical coupling components. Analytical calculation of the SCB is simplified and thus not highly accurate. Therefore, the finite element method simulation of the SCB is an important tool for understanding these effects without the danger of damaging the machine by experiments. In this paper, a suitable field formulation, modeling details, and simulation methods for dynamic analysis of synchronous machines are presented in detail. In particular, the accuracy of 2-D and 3-D transient electromagnetic simulations is analyzed by comparison against the available measurements performed on a chosen testing salient pole synchronous machine under the conditions of three-phase, two-phase, and single-phase short circuit. [ABSTRACT FROM AUTHOR]

The windings of power synchronous machines are often parallel connected to obtain the desired machine voltage and current ratings. Ideally, the split-phase currents are equal in symmetrical windings, so as to avoid parasitic circulation of current in the parallel branches. However, the symmetry is broken in case of rotor eccentricity, and the split-phase currents become unbalanced. Part I of this paper analyzed the theoretical behavior of the unbalanced currents by using symmetrical components. A new fault diagnosis method was shown, based on a combined space-vector/fast Fourier transformation (FFT) analysis of signatures in the split-phase currents. This Part II applies the split-phase current signature analysis to a laboratory 17-kVA synchronous generator with artificial faults. Method performances have been evaluated with mixed static/dynamic type fault, in no-load and loaded conditions. The experiments are matched with time-stepping finite-element simulations, which help explain the effect of saturation and load on the diagnosis accuracy. The feasibility of installation of current probes in practical machines is also discussed. [ABSTRACT FROM PUBLISHER]

This work shows a method to quantify rotor eccentricities in synchronous machines by exploiting the unbalance caused in the split-phase currents. The paper first develops a machine model comprehensive of eccentricities and parallel circuits in the stator, by using symmetrical components. Then, the model is used for formal calculation of the unbalanced currents. Finally, the equations are reversed to obtain eccentricity degrees from current measurements. Practical formulas are given for fault assessment, only requiring machine line voltage and synchronous reactance. The method can be applied on load. This paper provides full details of the theory underlying the method. The theory also clarifies some aspects about split-phase currents, not deepened before. It is proven that the air gap flux modulation due to eccentricities, acting through additional 2(p \pm 1)-pole flux waves in 2p-pole machines, stimulates additional currents, which circulate in the stator and turn into 2(p \pm 1)-pole rotating space vectors in the complex domain. Vector trajectories have shape and amplitude dictated by eccentricity type and degree, respectively. This study is limited to 2p-pole machines with p \geq 2. The theory is corroborated by simulations of a practical 1950-kVA generator in this paper. Experimental proofs and simulations of a laboratory 17-kVA machine are provided in a sequel of this paper. [ABSTRACT FROM PUBLISHER]

This paper presents an FPGA-based (Field Programmable Gate Array) sensorless controller for Surface Mounted Permanent Magnet Synchronous Machines (SMPMSM). A hybrid sensorless controller combining the signal injection technique and a linearly compensated flux observer is proposed. Using a Delta-Sigma A/D converter and FPGA oversampling technique, this work realizes a high performance high frequency (HF) injection sensorless control method which needs lower HF current response and introduces lower acoustic noises. The linearly compensated flux observer, based on back electromotive force (EMF) is used for sensorless control in the high speed range. The flux observer exhibits high dynamic and steady-state performance and is robust to parameter variation. Using model-based design, with the tools of MATLAB/Simulink and Simulink HDL (hardware description language) Coder, the whole control system is designed and implemented in a single chip. Experimental results demonstrate that the developed sensorless controller has high performance in the whole speed range. [ABSTRACT FROM PUBLISHER]

The growing demand for energy in the presence of remarkably limited resources, makes the task of power system operators increasingly difficult. This situation was exacerbated by a topology of these networks increasingly complicated. In this paper we present an analytical development of a new fuzzy control strategy applied to a Synchronous Machine (SM) connected to an electrical network, particularly during a failure affecting the Back to Back converter or an unbalance of the network voltage system. The foundations of this strategy is based on the estimation, in real time, of the voltage and current fluctuations that affect the operation mode just as well the SM as of the Back to back converter resulting from a serious event materialising by a loss of one leg of the grid side or the SM side converter. We have taken into account in our strategy possible dynamic behaviour of network components resulting from the appearance of a disturbance subject to random character action established by enhanced fuzzy controllers. [ABSTRACT FROM AUTHOR]

This paper extends previously proposed methods for frequency-domain analysis of subsynchronous oscillation phenomena in synchronous machines. Particular attention is given to the case where a current-controlled voltage-source converter is located electrically nearby. It is shown that the converter can contribute with significant positive electrical damping. Negative electrical damping is normally contributed only in the frequency region where the converter acts as a negative resistance. This region can be reduced or eliminated by proper design of the current controller. [ABSTRACT FROM AUTHOR]