Grid-tied voltage source inverters using LCL filter have been widely adopted in distributed power generation systems (DPGSs). As high-order LCL filters contain multiple resonant frequencies, ...switching harmonics generated by the inverter and current harmonics generated by the active/passive loads would cause the system resonance, and thus the output current distortion and oscillation. Such phenomenon is particularly critical when the power grid is weak with the unknown grid impedance. In order to stabilize the operation of the DPGS and improve the waveform of the injected currents, many innovative damping methods have been proposed. A comprehensive overview on those contributions and their classification on the inverter- and grid-side damping measures are presented. Based on the concept of the impedance-based stability analysis, all damping methods can ensure the system stability by modifying the effective output impedance of the inverter or the effective grid impedance. Classical damping methods for industrial applications will be analyzed and compared. Finally, the future trends of the impedance-based stability analysis, as well as some promising damping methods, will be discussed.
Social learning in particle swarm optimization (PSO) helps collective efficiency, whereas individual reproduction in genetic algorithm (GA) facilitates global effectiveness. This observation recently ...leads to hybridizing PSO with GA for performance enhancement. However, existing work uses a mechanistic parallel superposition and research has shown that construction of superior exemplars in PSO is more effective. Hence, this paper first develops a new framework so as to organically hybridize PSO with another optimization technique for "learning." This leads to a generalized "learning PSO" paradigm, the *L-PSO. The paradigm is composed of two cascading layers, the first for exemplar generation and the second for particle updates as per a normal PSO algorithm. Using genetic evolution to breed promising exemplars for PSO, a specific novel *L-PSO algorithm is proposed in the paper, termed genetic learning PSO (GL-PSO). In particular, genetic operators are used to generate exemplars from which particles learn and, in turn, historical search information of particles provides guidance to the evolution of the exemplars. By performing crossover, mutation, and selection on the historical information of particles, the constructed exemplars are not only well diversified, but also high qualified. Under such guidance, the global search ability and search efficiency of PSO are both enhanced. The proposed GL-PSO is tested on 42 benchmark functions widely adopted in the literature. Experimental results verify the effectiveness, efficiency, robustness, and scalability of the GL-PSO.
Recently, finite control set model predictive control (FCS-MPC) has been successfully applied in the grid-tied inverter with the LCL filter. However, to achieve active damping and grid ...synchronization, many sensors are required, increasing cost, and complexity. In addition, a considerable computational delay should be addressed when it is experimentally implemented, which may degrade the performance of the overall system. In order to reduce the number of sensors, eliminate the computational delay, and enhance the control reliability of the system, a novel FCS-MPC strategy with merely grid-injected current sensors is proposed, which contains four compositions: virtual flux observer, state observer, delay compensation, and FCS-MPC algorithm based on estimations. A 3-kW/3-phase/110-V experimental platform is established to validate that utilizing the proposed observations-based control method with only grid-injected current sensors is capable to obtain satisfactory performance of grid synchronization and high-quality grid-injected current both under balanced and unbalanced grid voltage condition.
This paper derives a circuit-level analytical model for describing the mechanism of the spurious triggering pulse in the gate-source voltage of the synchronous MOSFET (SyncFET) in the synchronous ...buck converter. The model takes into account not only the parasitic capacitances and inductances of the control MOSFET (CtrlFET) and the SyncFET, but also the reverse recovery characteristics of the body diode of the SyncFET. An exhaustive investigation into the impact of all these factors on the spurious triggering pulse is conducted. The spurious triggering pulse can be attributed to two factors. The first one is the positive gate voltage caused by the displacement current through the gate-drain capacitance of the SyncFET, due to the increase in the drain-source voltage. The second one is the negative source voltage caused by the voltage drop across the source inductance of the SyncFET, due to the decrease in the drain current. It is discovered that the gate impedance of the SyncFET would exert different influence on the magnitude of the spurious triggering pulse, depending on the contributions of these two factors. Experimental results affirm that variation in the magnitude of the spurious triggering pulse with each parasitic element can be correctly inferred by the proposed model. Design guidelines for enhancing spurious turn-on immunity are advanced.
Typical dc distribution networks contain source-interface dc-dc converters for feeding constant power loads (CPLs). Instability may arise if the interaction between the output impedance of the ...converters and the input impedance of the CPLs does not satisfy stability criteria. A simple technique that aims to deal with such issue is proposed. Instead of shaping the network characteristics with sophisticated control laws or introducing passive or active damping, the proposed idea is based on using an output filter with a nonlinear inductor in the converter to enhance small-signal and large-signal stabilities. First, the eigenvalues of the Jacobian at the equilibrium points can be maintained in the left-half plane. Second, the system state can always be reverted to the target operating point after large-signal perturbation. Furthermore, the physical size of the nonlinear inductor is comparable with that of the fixed-value inductor in the output filter without sacrificing ripple current requirement. The proposed method has been evaluated on a downscaled system with the power level of 80 W and bus voltage of 24 V. The experimental results are in good agreement with the theoretical predictions.
A disruptive technology fundamentally transforming the way that computing services are delivered, cloud computing offers information and communication technology users a new dimension of convenience ...of resources, as services via the Internet. Because cloud provides a finite pool of virtualized on-demand resources, optimally scheduling them has become an essential and rewarding topic, where a trend of using Evolutionary Computation (EC) algorithms is emerging rapidly. Through analyzing the cloud computing architecture, this survey first presents taxonomy at two levels of scheduling cloud resources. It then paints a landscape of the scheduling problem and solutions. According to the taxonomy, a comprehensive survey of state-of-the-art approaches is presented systematically. Looking forward, challenges and potential future research directions are investigated and invited, including real-time scheduling, adaptive dynamic scheduling, large-scale scheduling, multiobjective scheduling, and distributed and parallel scheduling. At the dawn of Industry 4.0, cloud computing scheduling for cyber-physical integration with the presence of big data is also discussed. Research in this area is only in its infancy, but with the rapid fusion of information and data technology, more exciting and agenda-setting topics are likely to emerge on the horizon.
Determining how to efficiently obtain superior transient response under both unidirectional power-changing and power-reversing operations in a bidirectional dual-active-bridge (DAB) dc/dc converter ...is a challenging problem. The traditional direct phase-shifting scheme would induce a transient dc current bias in the high-frequency link of the DAB, and therefore, lead to some adverse issues, such as magnetic saturation and increased current stress. In addition, the ac transient can propagate to the dc terminates and give rise to a worse transient response in a closed-loop control system. In this article, a fast phase-shift control is proposed that can execute all the possible power changes in a unified manner. By properly operating the primary bridge with pulsewidth modulation (PWM) and the secondary bridge with pulse frequency modulation (PFM), the DAB converter can complete the phase-shifting operation fast without a dc current bias in the ac link. A closed-loop control based on the hybrid PWM/PFM is further designed to regulate the primary dc current with improved transient performance. Since both PWM and PFM are standard, the whole control algorithm can be implemented efficiently in practical applications. The experimental results are provided to show that the power of the DAB converter can be governed bidirectionally with the proposed phase-shift control. The dc-terminal current can be changed to both polarities with fast transient and no apparent overshoot or oscillation.
A single-phase transformerless full-bridge photovoltaic grid-tie inverter is presented. It utilizes 1) a virtual ground technique to mitigate ground leakage current, 2) a hybrid pulsewidth modulation ...(HPWM) scheme to profile the output current and prevent sudden changes in the common-mode voltage, and 3) a nonlinear output inductor to attenuate current ripple around zero crossings and minimize filter size. The HPWM is effectively the same as unipolar PWM (UPWM), but with soft voltage transition modulation introduced around the zero crossings. Apart from low switching losses, the output filter is implemented with a minimum number of components to achieve high attenuation of ripple current. By deriving the switching trajectory, a mathematical model is formulated, and the ground leakage current and the output current with the traditional UPWM and the proposed HPWM schemes are compared. The output current harmonics caused by the nonlinear output inductor is analyzed by the Volterra theory. A 340 W, 380 Vdc/110 V ac, 50 Hz prototype has been built and evaluated.
This paper presents a comprehensive study on the influences of parasitic elements on the MOSFET switching performance. A circuit-level analytical model that takes MOSFET parasitic capacitances and ...inductances, circuit stray inductances, and reverse current of the freewheeling diode into consideration is given to evaluate the MOSFET switching characteristics. The equations derived for emulating MOSFET switching transients are assessed graphically, which, compared to results obtained merely from simulation or parametric study, can offer better insight into where the changes in switching performance lie when the parasitic elements are varied. The analysis has been successfully substantiated by the experimental results of a 400 V, 6 A test bench. A discussion on the physical meanings behind these parasitic effect phenomena is included. Knowledge about the effects of parasitic elements on the switching behavior serves as an important basis for the design guidelines of fast switching power converters.
Piezoelectric shunt damping is widely studied to suppress vibration of thin structures via shunting an attached piezoelectric transducer with an electrical impedance. The synchronized switch damping ...on voltage (SSDV) technique can be used to enhance the damping effect. However, SSDV is not stable in the weak excitation. Although some adaptive SSDV circuits have been developed to tackle the stability problems, additional monitoring devices are required to provide feedback for the vibration strength signal for adjusting the series voltage sources. We here present a new direct adaptive SSDV (DA-SSDV) method without an additional excitation level monitoring module, based on the ratio of the maximum piezo voltage and the value of the series voltage sources. A compact DA-SSDV circuit is designed with low-cost off-the-shelf discrete components. The closed-loop control of the series voltage sources is realized simply through a passive envelope detector and a resistive voltage divider. Experimental results show that the DA-SSDV circuit avoids the stability problems and possesses good displacement transmissibility around 6.2, a fast voltage adjustment response speed above 5 V/s, and high operation sensitivity with the open-circuit piezo voltage of 540 mV. The DA-SSDV shows great application value in compact and low-power vibration control systems.
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