ABSTRACT— This work presents a novel single phase cascaded H-bridge multilevel inverter with least number of switches and isolated DC sources. The proposed inverter consists of two H-bridges connected in cascade. The upper H-bridge consists of five power electronic switches, capable of developing five level output and the lower H-bridge is capable of developing multilevel output. The conventional CHB inverter is replaced with the additional bi-directional switches in each cell. The proposed inverter consists of two H-bridges, the upper H- bridge is replaced with the addition of one bi-directional switch and the lower H-bridge is replaced with the bi- directional switches driven by hybrid modulation switching strategy. The upper inverter is switched at high frequency and the lower inverter is switched at low frequency. Hybrid modulation switching strategy is used to generate the multilevel output for the proposed inverter. The proposed inverter will be compared with the existing multilevel topologies on the basis of number of components, number of isolated DC sources, Switching losses and converter losses. The proposed inverter will be connected to the grid by proper synchronization along with maximum power point tracking algorithm. The proposed grid connected multilevel inverter will be simulated using MATLAB/SIMULINK and will be implemented in hardware using SPATRAN3A DSP. KEYWORDS— Cascaded inverters, Hybrid modulation, maximum power point tracking, Bi-directional switch.
Traditional beamforming strategy uses the same beam- forming vector to align information resources and energy resources, which does not consider the diversity of resources in the SWIPT system and the utilization of interference. This results in a waste of system resources. In this paper, a joint beamforming strategy based on SWIPT system has been proposed, which realizes the independent control of information resources and energy resources and reduces the mutual restraint between the two resources. As a result, the interference in the SWIPT system is effectively used. In order to eliminate the interference, we still use the zero-forcing beamforming strategy with the information beamforming vector, and we need not consider the energy beamforming vector too much. In this paper, we propose a TPO problem with complex constraints, which is a non-convex prob- lem. Experimental results show that the joint beamform- ing strategy can achieve a better energy collection at the same transmission power of the base station and can also attain a less transmission power at the same energy collection.
11 Read more
Now that we have satisfied ourselves that regardless of the exact mechanism which occurs at the switching level we get the same net effect on the inductor current for the introduction of a phase shift we can use the calculated inductor current to investigate the effects on the DC bus voltage. We can with confidence say that for an increasing inductor current magnitude and a reducing phase shift between the inductor current and the grid voltage there will be an increase in the active power flow. To demonstrate this in terms of the DC bus voltage behaviour we will use the calculated inductor current to calculate the instantaneous charge flowing to/from the capacitor and thus determine the effect of the phase shift on the charge/discharge of the DC bus capacitors. The charge flowing into the capacitor can be found using;
179 Read more
Two novel core-switching rearrangements to natural product-like privileged scaffolds that proceed in up to 99% yield have been developed. The deviation away from planarity of the central N-acyl urea carbonyl, caused by the structure of the medium- sized ring, dictates the exclusive reaction outcome. Proposed mechanisms and products for the reaction pathways are supported by small molecule X-ray crystallography and an isolated intermediate. Twenty-four novel rearrangement products are reported.
41 Read more
ABSTRACT: Multilevel Inverters (MLI) are suitable for high voltage and power applications because they can reduce voltage stresses and harmonic contents. Generally cascaded hybrid MLIs uses sinusoidal PWM strategies to generate multiple dc levels in the sinusoidal AC output for the reduced THD. In this paper 55 level Quasi Hybrid Cascaded Multilevel Inverter (QHCMLI) is developed with sinusoidal PWM strategy using simulink model. The obtained results are evaluated by the performance measures such as THD, root mean square, crest factor, form factor and distortion factor for various modulation index and shows that the performance QHCMLI using POD PWM scheme is satisfactory. QHCMLI is also designed with the proposed PWM strategy using reference signals generated by switching angle method and the simulated outputs are validated by comparing the performance with the conventional PWM strategy using the proposed PWM switching strategy the performance measure of PD, POD, and APOD is improved than the previous methods for high modulation index.
To implement this, we have to compute θ i (v) for all i ∈ [D]. This can be done using the same strategies as were discussed above in a good dimension, using either hoisting or iteration. The only other automorphism we need to compute is one evaluation of θ −D . Note that with our new key-switching strategy (see Section 4.3), we always have available a key-switching matrix for θ −D . If we ignore the cost of pre-computing all the constants in DoubleCRT format, we see that the computational cost is roughly the same in both good and bad dimensions. This is because the time needed to perform all the constant-ciphertext multiplications is very small in comparison to the time needed to perform all the automorphisms. The cost in noise is also about the same, essentially, one constant-ciphertext multiplication.
25 Read more
Motivated by the above discussion, this paper focus on solving the finite-time stabilization problem for nonholonom- ic mobile robots subject to spatial constraint. The contri- butions can be highlighted as follows. (i) The finite-time stabilization problem of nonholonomic systems with spatial constraint is studied for the first time. (ii) A nonlinear mapping is introduced, under which the constrained interval is mapped to the whole real number field. (iii) Based on a switching strategy to eliminate the phenomenon of uncon- trollability of u 0 = 0, and by skillfully using the adding
This paper presents Space Vector based switching strategy for a STATCOM that utilizes the voltage source converter to minimize the harmonic at the point of common contact. The entire design of STATCOM and SVPWM is done in harmonic domain for calculation of harmonic interference in the system and evaluated based harmonic domain algorithms using MATLAB code.
(19) where is the zero vector boundary. In other words, a zero vector is applied at any sampling instant at which the current error vector falls inside the boundary. By using this strategy, at low rotational speeds, most sampling periods are occupied by zero vectors, whilst at high rotational speeds, the application of a nonzero vector of opposite polarity to that of the back-emf is replaced by a zero vector, without the need for back-emf information. Fig. 4(b) shows a schematic of the modified CRDM strategy according to (19). On the one hand, if all the phase current errors are less than , the comparators result in “ .” However, selection of the zero vector at the next output state depends on the previous voltage vector, i.e., at most, only one switching-state signal is allowed to change for the next zero vector. This is referred to as optimum zero-vector selection. On the other hand, if any current error exceeds the band, an appropriate nonzero vector whose direction reduces the current error magnitude is used. In the steady state, considering (17)–(19), and assuming that the magnitude of the back-emf never reaches , it will be seen that (low speed) is still governed by (15). However, as mentioned earlier, since a nonzero vector having the opposite polarity to that of the back-emf is never applied, the magnitude
11 Read more
Abstract: The DC-AC converter, also known as the inverter, converts DC (Direct Current) power to AC (Alternating Current) power at desired output voltage and frequency. The inverter therefore is an adjustable-frequency voltage source. The project aims to design a FPGA implement Neuro-Fuzzy based 1-ϕ square wave voltage source inverter using Pulse Width Modulation (PWM) switching scheme to supply AC utilities with emergency power. A model of the voltage source Inverter using a pair of MOSFETs and a driver circuit is designed; then to increase its performance, a fuzzy controller (FC) which its parameters are adjusted by a basis neural network (NN) function. The VHDL (VHSIC Hardware Description Language) code for the system was written and behavioral simulation was performed on the architecture whose results were seen in ModelSim software. After verifying the results this VHDL code was downloaded to ALTERA FPGA (Field Programmable Gate Array) and synthesized using Quartus II software. After downloading the code in FPGA real time debugging was done for the architecture. The focus is on designing an inexpensive, versatile and power efficient square wave inverter that gives a square wave AC output.
12 Read more
the error in both the inductor current and capacitor voltage . In many applications of Modulated MPC (M2PC) one cost function is used to select the vectors and duty cycles in every sampling period. Once calculated the duty cycles are then applied in the following switching period, a method which leads to the possibility of emulating SVM whilst by using a MPC implementation , . These methods give the combined advantages of MPC in terms of fast transient response, multi-objective control and the ability to cope with non-linearities whilst also allowing the control to minimise control variable ripple and fix the switching frequency to allow the realistic design of filter components.
In this paper, we forecast the volatility of gold prices using Markov Regime Switching GARCH (MRS-GARCH) mod- els. These models allow volatility to have different dynamics according to unobserved regime variables. The main pur- pose of this paper is to find out whether MRS-GARCH models are an improvement on the GARCH type models in terms of modeling and forecasting gold price volatility. The MRS-GARCH is best performance model for gold price volatility in some loss function. Moreover, we forecast closing prices of gold price to trade future contract. MRS- GARCH got the most cumulative return same GJR model.
11 Read more
The evicting host determines the minimum amount of CPU required to be available on another host to evict one of its VMs and relieve the stress situation. CPU is measured in CPU units, as described in Chapter 2. It then broadcasts a Resource Request message to all hosts, containing this value. To conserve bandwidth when broadcasting Resource Request messages, we choose to send the minimum required available CPU only as it is a good indication of overall load, and is highly contentious. Each host determines if it has enough CPU remaining to accommodate the minimum request, as well as ensuring that its memory is not full. If it passes these checks, it responds to the evicting host with a Resource O ff er. The Resource O ff er message contains the total amount of resource available, for all resources (not just CPU), which may be higher than the original request. The evicting host waits a specified time for responses, and then selects a VM and a target host using a first-fit heuristic algorithm. The algorithm is similar to Algorithm 1, except that each stressed host performs the algorithm itself, and the target list contains only those offering hosts who responded to the Resource Request. That is, sources (line 2) contains only the evicting host, and the set of hosts H classified in line 1, which are used for target hosts, contains only offering hosts. Once a VM and target have been chosen, notification of the decision is sent to all o ff ering hosts (so they may return to the normal state), and the migration is performed. The sorting of VMs and targets is done as specified for the Hybrid strategy in Chapter 3.3.3.
137 Read more
The development of existing hybrid control strategies is gaining a high momentum, especially for a grid-off application. Various mathematical modelings as well as different types of designs and simulation results of hybrid renewable energy system have been published. Recently, most of the systems are controlled by a mean of rule-based strategy acting on common DC bus and thus influenced the whole system performance . On the other hand, the combination controlled strategy patterned at both AC/DC buses has also been introduced. The concept of hybrid AC/DC system is hence emerging to combine the benefits of both types, while reducing losses by avoiding multiple power-electronic conversion stages and increase the system reliability .
12 Read more
Abstract: This paper presents the mechanism and robust control of a monolithic wire clamp to achieve fast and precision operations for strong androbustmicro device packaging. The wire clamp is piezoelectrically actuated and a two-stage flexure-based amplification was designed to obtain largeandparallel jaw displacements. The grasping forces of the wire clamp were evaluated based on finite element analysis (FEA), and the force measurement was presented. The wire clamp was manufactured using wire EDM technique and the position and force transfer functions were obtained based on the frequency response approach. The position/force switching control strategy was employed to regulate the motion position and grasping force, and the position/force switching controller composed of a PID controller for position control and a sliding model controller (SMC) for force control was designed. Experimental tests were carried out to investigate the performance of wire clamp with the position/force switching controllerduring the grasping and releasing operations. The results show that the wire clamp exhibits good performance and demonstrate that high speed and precision grasping operations can be realized through the developed wire clamp and the control strategy. Keywords: Wire clamp, flexure mechanism, mechanical design, position/force regulation
35 Read more
– but also the variance of such data. In many cases it is simply impossible to obtain such data with a sufficiently reliability. For this reason, we think that, in some conditions, introducing in the decision-making process some “switching rules” on demand levels might be a good way to manage “on the road” the uncertainty of forecasts. Ideally, it is like reducing year by year the variance (the uncertainty) of demand forecasts by observing the actual demand and taking decisions on new expansions consequently. The payoff is the extra-cost associated to phased projects. It can be estimated ex-ante by engineers and compared with the quantifiable flexibility benefits (in some cases, it can even be near-to-zero, in linear capacity expansion projects like the Turin – Lyon freight line). The tool to make this comparison can be, as we showed, the CBA in the usual form that reveals perfectly adapt to manage such rules in a reasonably simple way.
16 Read more
Moreover, the result of this study provides empirical evidence of how NL switching functions as a cognitive compensatory strategy which supports the results of the previous reviewed studies. They found that L2 students integrated their NL for the function of compensating L2 linguistic problems. However, the previous study results did not reveal how the strategies were employed by the learners. This constitutes another different finding from the current study. One thing is apparent from this study is that the learners' reliance on their NL functions as solution to the problems they have with the lexical and grammatical complexities of the TL and they do it through NL switching, code mixing, literal translation, and foreignizing. These four cognitive compensatory strategies were used to make up for their insufficient linguistic repertoire in order to achieve the written communication goal. Cook (2016) states that NL switching is psychologically-motivated strategy for solving the individual's L2 problem of expression. Meanwhile, Gou (2014) states that it is unrealistic to avoid NL in the process of learners’ interlanguage development as this cognitive mechanism can facilitate learning. In other words, students use NL as coping strategy for the mismatch between their
Applications are shifting into large scale, virtualized data centres that provide resources on a pay-per-usage basis. With power consumption representing a major operational cost, data centres must prioritize efficiency while still providing enough resources to meet application requirements. To meet variable application demands, a dynamic approach to virtual machine (VM) management is required. This requires: (i) placing newly arrived VMs, (ii) migrating VMs from highly utilized machines to avoid performance degradation, and (iii) migrating VMs from underutilized machines so that they may be deactivated to save power. Here, a management strategy is considered to be a policy-set that guides these three operations. To achieve the conflicting goals of performance and efficiency, I propose and evaluate a system of dynamically switching between two management strategies, each with a single goal, based on trends in data centre workload. Experimentation over a simulated data centre demonstrates the superiority of this approach over single-strategy techniques.
67 Read more
The energetic benefits of diurnality proposed by the CTE hypothesis would be most relevant for animals challenged to maintain energy balance. Indeed, a literature review on temporal niche switching found that most temporal niche switches occurred in typically nocturnal mammals under conditions of increased energetic requirements (e.g. winter cold or food scarcity) (Hut et al., 2012). To investigate how metabolic demand shapes circadian organization, we developed the ‘ working for food ’ protocol (WFF) in which mice are subjected to conditions of simulated food shortage (Hut et al., 2011). Mice subjected to WFF have to obtain their food by working in a running wheel and become increasingly day active when the workload increases (Hut et al., 2011). This allows daily torpor bouts to occur during the second half of the night in mice challenged energetically for prolonged periods (Hut et al., 2011). The increased daytime activity is more pronounced when combined with other energetic challenges such as lowered T a (van
it to adapt to the context of DNC. Agent-based simulations of diﬀerent strategies are per- formed to obtain the optimal one for DNC. The result suggests that, in a situation where some key information is rare (known only to a few sources), the IntEstim strategy outper- forms the others on average, no matter what conﬁdence level is deﬁned. It also agrees with the ﬁndings of other studies  that -greedy strategy and its variants have very similar performance, and making decreasing would not improve that. On the other hand, if all key information has similar number of appearances, highly exploitative -greedy strategy and its variants could be the most promising strategies. Given that general time-critical social search problems usually have unknown reward distribution and switching cost, we suggest adopting highly exploitative -greedy strategy and its variants.
14 Read more