Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 7 Articles
A unique direct driven permanent magnet synchronous generator has been designed and constructed. Results from simulations as well as from the first experimental tests are presented. The generator has been specifically designed to be directly driven by a vertical axis wind turbine and has an unusually low reactance. Generators for wind turbines with full variable speed should maintain a high efficiency for the whole operational regime. Furthermore, for this application, requirements are placed on high generator torque capability for the whole operational regime. These issues are elaborated in the paper and studied through simulations. It is shown that the generator fulfils the expectations. An electrical control can effectively substitute a mechanical pitch control. Furthermore, results from measurements of magnetic flux density in the airgap and no load voltage coincide with simulations. The electromagnetic simulations of the generator are performed by using an electromagnetic model solved in a finite element environment....
Accurate current control of the voltage source converters (VSCs) is one of the key research subjects in modern power electronics. To achieve a preferable solution to current coupling effect in the VSC-based three-phase three-line system, a discrete-time decoupled current control strategy is proposed in the paper. With integration of the a-�Ÿ transform and two independent current controllers, the proposed methodology can effectively implement decoupled control of the three-phase currents, which can thereby eliminate the impact from the neutral-point voltage especially under asymmetrical loading conditions. Control performance under digital realization was characterized with extensive tests on a shunt active power filter (SAPF) platform. Both the simulative and experimental results have demonstrated that the SAPF could function well and thereby verified the feasibility and effectiveness of the proposed current control methodology....
An efficient power factor correction converter is presented. Two boost-topology switching cells are interleaved to minimize EMI while operating at lower switching frequency and soft switching to minimize losses. The result is a system with high conversion efficiency, able to operate in a pulse-width-modulation (PWM) way. Seven transition states of the ZVT converter in one switching period are described. In order to illustrate the operational principle key, implementation details, including simulations, are described. The validity of this converter is guaranteed by the obtained results....
The static synchronous compensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using GTOs employed for reactive power control. A typical application of a STATCOM is for voltage regulation at the midpoint of a long transmission line for the enhancement of power transfer capability and/or reactive power control at the load centre. The PI controller-based reactive current controller can cause oscillatory instability in inductive mode of operation of STATCOM and can be overcome by the nonlinear feedback controller. The transient response of the STATCOM depends on the controller parameters selected. This paper presents a systematic method for controller parameter optimization based on genetic algorithm (GA). The performance of the designed controller is evaluated by transient simulation. It is observed that the STATCOM with optimized controller parameters shows excellent transient response for the step change in the reactive current reference. While the eigenvalue analysis and controller design are based on D-Q model, the transient simulation is based on both D-Q and 3-phase models of STATCOM (which considers switching action of VSC)....
A pulse-width modulator to drive three-phase AC motors is described. It performs a numerical modulation technique, also known as optimum or calculated modulation, but, in order to reduce hardware resources, a hybrid approach merging that calculated modulation with proportional modulation is proposed. The modulator is tested in a flash-based field programmable gate array (FPGA) implementation....
The advent of series FACTS controllers, thyristor controlled series capacitor (TCSC) and static synchronous Series Compensator (SSSC) has made it possible not only for the fast control of power flow in a transmission line, but also for the mitigation of subsynchronous resonance (SSR) in the presence of fixed series capacitors. SSSC is an emerging controller and this paper presents SSR characteristics of a series compensated system with SSSC. The study system is adapted from IEEE first benchmark model (FBM). The active series compensation is provided by a three-level twenty four-pulse SSSC. The modeling and control details of a three level voltage source converter-(VSC)-based SSSC are discussed. The SSR characteristics of the combined system with constant reactive voltage control mode in SSSC has been investigated. It is shown that the constant reactive voltage control of SSSC has the effect of reducing the electrical resonance frequency, which detunes the SSR. The analysis of SSR with SSSC is carried out based on frequency domain method, eigenvalue analysis and transient simulation. While the eigenvalue and damping torque analysis are based on linearizing the D-Q model of SSSC, the transient simulation considers both D-Q and detailed three phase nonlinear system model using switching functions....
Novel method of space-vector-based pulse-width modulation (PWM) has been disseminated for synchronous control of four\r\ninverters feeding six-phase drive on the base of asymmetrical induction motor which has two sets of windings spatially shifted by\r\n30 electrical degrees. Basic schemes of synchronized PWM, applied for control of four separate voltage-source inverters, allow both\r\ncontinuous phase voltages synchronization in the system and required power sharing between DC sources. Detailed MATLABbased\r\nsimulations show a behavior of six-phase system with continuous and discontinuous versions of synchronized PWM....
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