Two-degree-of-freedom (2-dof) proportional-integral-derivative (PID) controllers are better than the 1-dof counterpart in the sense that the former can predominantly reduce large overshoot and settling time without affecting the steady-state performance provided that a suitable tradeoff is chosen between reference tracking and rejection of the disturbance signal. Again, fractional order (FO) calculus is suitable to realize the dynamics of a controlled system and smoothen control action. This article amalgamates both of these control actions and develops a novel 2-dof FOPID controller for stabilization and precise position control of an unstable and nonlinear magnetic levitation system. A set of frequency-domain parameters are optimized to evaluate controller's orders and gains by adopting equilibrium optimizer, a new and efficient technique in the field of modern metaheuristics algorithms. It has been observed that the proposed 2-dof control architecture outperforms the 1-dof control counterpart in terms of time- and frequency-domain indices, reference tracking, robust stability analysis, and cancellation of disturbance signal. The efficacy of the proposed controller has been verified by comparing performance characteristics with existing controllers both in simulation and experimentation.

This paper presents a comparative analysis of two popular control approaches, namely, Classical Control and Model Predictive Control (MPC) applied to a bidirectional quasi Z-Source converter (qZSC). The paper describes the topology of the bidirectional quasi Z-source converter, the basic philosophy of classical control, and the basic concept of model predictive control. The small signal models of the qZSC required for design of classical controllers, and discrete predictive models of the qZSC required for the MPC are also presented in this paper. Using these models and control algorithms, the systems were simulated in Matlab/Simulink and the results were compared. The comparisons were performed on the basis of transient and steady state response, robustness to parameter variations, and harmonic content of the resultant output waveforms. The comparative analysis shows that both the approaches have certain strengths and weaknesses and one may be chosen over the other based on varieties of factors.

This paper presents design, fabrication and testing of a Two-Phase Interleaved Boost Converter (IBC) with Type-III controller by utilizing voltage mode control. The small-signal modeling of IBC is derived in continuous conduction mode (CCM) of operation. A right half plane (RHP) zero is appeared in the control to output plant transfer function of the IBC. Due to non-minimum phase problem, the Type-III controller is designed by using ‘k’ factor approach and is implemented for closed loop operation of IBC for achieving better dynamic performance and stability. The closed loop IBC with designed Type-III controller is fabricated and tested in the laboratory. Simulation and experimental results have been produced to show the efficacy of the proposed converter control system.

A carrier based discontinuous pulse width modulation (DPWM) strategy for capacitor voltage balancing in a three level neutral point clamped (NPC) traction inverter drive for Electric Vehicles (EVs) is developed and presented in this paper. The voltage unbalance is compensated by injecting an offset signal with the three phase reference voltages. The offset signal is derived from the three phase stator currents and capacitor voltage differential. The scheme requires only single carrier and two auxiliary signals per phase for implementation. The proposed modulation scheme exhibits good control over two dc link capacitor voltages for a wide range of torque-speed variations. The effectiveness of the proposed scheme are verified through simulation by developing a MATLAB/SIMULINK model for induction motor (IM) based traction inverter drive while employing indirect field oriented control (IFOC) strategy for closed loop control. Finally, the modulation scheme is validated through experimentation in a small scale prototype NPC inverter.

A Carrier Based Double Signal PWM (CB-DSPWM) scheme in conjunction with a zero sequence signal to mitigate voltage unbalances at neutral point (NP) for three-level NPC converters is proposed. The scheme compensates the dc link capacitor voltage unbalances and eliminates the low frequency voltage oscillations at NP that appear under certain operating conditions of the converter. The voltage balancing is achieved by adding a zero sequence current component with the zero sequence voltage. Injection of the modified zero sequence with the modulation signal produces substantial average neutral current for all power factor (PF) angles. By incorporating the proposed PWM scheme, improved NP voltage balancing for full PF range and at high modulation indices are achieved. The dynamic performances of the proposed scheme are evaluated through simulation in MATLAB/SIMULINK and the practicability of the proposed algorithm is validated through experimental results.

Electromagnetic levitation system (EMLS) is inherently unstable and strongly non-linear in nature. In majority cases the closed loop system has been stabilized by classical controller utilizing linearlized model of EMLS. The linear classical controller has a restricted zone of operation. But it is essential to design a control scheme so that EMLS can operate for a large air-gap stably and at the same time the performance of controller will be satisfactory irrespective of any change in operating air-gap. This paper reports design, implementation and testing of piecewise linear control schemes to extend the range of operating air-gap for a voltage controlled (EMLS) in real time environment through dSPACE.

In this paper a practical demonstration for simultaneous lévitation and rotation for a ferromagnetic object is presented. A hollow steel cylinder of 59 gm mass is arranged to remain suspended stably under I-core electromagnet utilizing DC electromagnetic levitation principle and then arranged to rotate the levitated cylinder around 1000 rpm speed based on eddy current based energy meter principle. Since the object is to be rotating during levitated condition the device will be frictionless, energy-efficient and robust. This technology may be applied to frictionless energy meter, wind turbine, machine tool applications, precision instruments and many other devices where easy energy-efficient stable rotation will be required. The cascade lead compensation control scheme has been applied for stabilization of unstable levitation system.

DC-DC converters lie at the heart of power electronic systems, finding usage in popular applications like Switched Mode Power Supplies (SMPS). Such demanding applications invariably require constant voltage irrespective of any changes on the load or input side. The un-modeled dynamics and external/internal disturbances make this objective even more challenging. This puts strict restrictions on the design of controllers and opens up avenues for research in this domain. In this paper, three control algorithms have been implemented to achieve better voltage regulation for buck converter. Classical PID controller is compared with Sliding Mode Controller (SMC) and Internal Model Controller (IMC). The converter response with these control archetypes has been compared under supply voltage variations, load changes and parametric variations. Internal Model Control emerges as a superior controller amongst the considered control algorithms with fast response and excellent steady state characteristics. Simulation results establish that Internal Model based controller is able to reject wide range parametric disturbances with negligible deterioration of output.

In this paper the analysis, design and fabrication of 3-coil based DC attraction type levitation scheme has been presented. In vehicle applications majority works have been reported based on four actuators based electromagnetic levitation system (EMLS). But in this prototype three electromagnets have been used at the three sides of the platform. The use of one magnet-coil, power amplifier and associated gate driver, controller circuit, position and current sensor is dispensed with the prototype. So there is considerable reduction of cost and weight of the proposed system and the hardware circuit is also simpler than four-coil structure. The objective is to levitate a platform under ferromagnetic guide-way normally used in electromagnetically levitated vehicle structure. The prototype (total mass 7.528kg) consists of three identical electromagnets placed at the three sides of a platform and the structure is made to remain suspended at different air-gap positions under a ferromagnetic guide-way - the arrangement that is normally used for EMLS. The structure of the levitated system has been constructed in-house. The three actuators have been controlled simultaneously by three similar single input single output (SISO) controllers utilizing the cascade Lead compensation control scheme. The design and implementation of the controller for such an unstable and non-linear system is the main aim of this study. The stable levitation has been demonstrated of the platform around an operating point.

In this paper the optimized parameters of Lag-Lead and Proportional Integral Derivative (PID) controller for two-actuator based electromagnetic levitation system (EMLS) are determined using Evolutionary computation algorithms such as Particle Swarm Optimization (PSO) and a novel Gravitational Search algorithm (GSA). A comparative position response of EMLS (Electro Magnetic Levitation System) with classical, GSA and PSO based nominal controllers while operating at nominal and off-nominal (low and high) air-gaps have been studied. It is seen that GSA based optimized nominal PID controller shows excellent performance (both in transient and steady-state) over a large operating air-gap. The experimental results with the classical controller are also presented.

A new, fault-tolerant, scalable, and modular virtual topology for lightwave networks employing wavelength division multiplexing is proposed. The proposed architecture is based on a hypercube connected ring structure that enjoys the rich topological properties of a hypercube , but it also overcomes one of its drawbacks. In a hypercube, the nodal degree increases with the number of nodes. Hence, the per-node cost of the network increases as the network size grows. However, in a hypercube connected ring network (HCRNet) the nodal degree is small and it remains constant, independent of the network population. A HCRNet, like a hypercube, is perfectly symmetric in the sense that the average internodal distance in an N -node HCRNet is the same from any source node. Its average internodal distance is in the order of log N and it is comparable to other regular structures such as the Trous and ShuffleNet. The HCRNet is based on the Cube Connected Cycle (CCC) interconnection pattern proposed for multiprocessor architectures. However, the HCRNet improves on CCC by rearranging its hypercube links, which results in a significantly lower average internodal distance. In this paper we present the structural properties of HCRNet, and address the issues of scalability, and fast routing in complete as well as incomplete HCRNet.

We consider the problem of designing logical optical network topology for a given physical topology (or fiber layout) and a given traffic demand matrix between the end-users. Traffic between the end-users is carried in a packet-switched form and the objective of our logical topology design is to minimize the maximum congestion on the logical links in the logical topology. The logical links are realized by wavelength continuous paths or between end-users and they are routed via wavelength-selective routers. Note that a topology with lower maximum link congestion will allow its traffic demand matrix to be scaled up by a larger factor. In the logical topology, each node is equipped with a limited number of optical transceivers, hence logical connections cannot be set-up between every pair of nodes. In this paper we present an analytical model for obtaining the maximum and average logical link loads for a given logical network and traffic demand matrix. The model is confirmed via simulation. A heuristic algorithm for constructing a logical topology that reduces maximum logical link congestion is also presented.

We consider the problem of routing and assignment of wavelength (RAW) in optical networks. Given a set of requests for all-optical connections (or lightpaths), the problem is to (a) find routes from the source nodes to their respective destination nodes, and (b) assign wavelengths to these routes. Since the number of wavelengths is limited, lightpaths cannot be established between every pair of access nodes. In this paper we first consider the dynamic RAW problem where lightpath requests arrive randomly with exponentially distributed call holding times. Then, the static RAW problem is considered which assumes that all the lightpaths that are to be set-up in the network are known initially. Several heuristic algorithms have already been proposed for establishing a maximum number of lightpaths out of a given set of requests. However most of these algorithms are based an the traditional model of circuit-switched networks where routing and wavelength assignment steps are decoupled. In this paper a new graph-theoretic formulation of the RAW problem, dubbed as layered-graph, has been proposed which provides an efficient tool for solving dynamic as well as static RAW problems. The layered-graph model also provides a framework for obtaining exact optimal solution for the number of requested lightpaths as well as far the throughput that a given network can support. A dynamic and two static RAW schemes are proposed which are based on the layered-graph model. Layered-graph-based RAW schemes are shown to perform better than the existing ones.

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied.>

A new, fault-tolerant, scalable, and modular virtual topology for lightwave networks employing wavelength division multiplexing is proposed. The proposed architecture is based on a hypercube connected ring structure that enjoys the rich topological properties of a hypercube, but it also overcomes one of its drawbacks. In a hypercube, the nodal degree increases with the number of nodes. Hence, the per-node cost of the network increase as the network size grows. However, in a hypercube connected ring network (HCRNet) the nodal degree is small and it remains constant, independent of the network population. The HCRNet, like the hypercube, is perfectly symmetric in the sense that average internodal distance in an N-node HCRNet is the same from any source node. Its average internodal distance is in the order of logN and it is comparable to other regular structures such as Trous and ShuffleNet. The authors present the structural properties of the HCRNet and the network routing.>

The authors exploit the capabilities of lightwave technology in order to construct photonic implementations of "adaptive" and "optimized" distributed queue dual bus (DQDB) structures. These (virtual) structures are linear and multihop in nature, and they can be constructed on any physical topology by exploiting the broadcast-and-select property of WDM lightwave networks. The present study is important since it will allow DQDB (IEEE 802.6) networks to scale up by taking advantage of the various attractive properties of lightwave technology when they become available. The specific problem is on topological design, and it can be stated as follows: given that the network nodes must be connected linearly and that the node positions in the network can be adjusted by properly tuning their (optical) transmitters and receivers, what is the best pattern for interconnecting them? Two sets of heuristic optimization algorithms are formulated. The first set is concerned with minimizing the maximum flow in any link. The second set of heuristics requires the knowledge of not only the traffic matrix but also the distance matrix, and these heuristics are aimed at minimizing the network-wide mean packet delay. A dynamic node migration heuristic is also formulated under which neighbouring nodes swap their positions based on local information in order to preserve the optimality criterion in effect when the offered traffic changes. The performance of these heuristics are compared, some of their properties are analyzed, while their other attractive properties are highlighted via numerical examples.>

The unique capabilities of lightwave technology are exploited in order to construct optimized regular multihop networks when the traffic flow among the network nodes is asymmetric. The specific problem addressed is as follows: given that the network nodes must be connected in a regular interconnection pattern and that the node positions in the regular network can be adjusted by properly tuning their (optical) transceivers, what is the best node placement in a given regular topology? In particular, the ShuffleNet-based regular topology is examined. ShuffleNet has the property of producing large connected graphs with small degree and diameter. In order words, it can interconnect a large number of nodes with a small number of transceivers per node such that information from a source can reach its destination in a small number of hops. Since finding the optimal node placement is a computationally hard problem, efficient heuristic algorithms are formulated to design optimized ShuffleNet structures for a given traffic matrix.>

The unfairness problem of the distributed queue dual bus (DQDB) (IEEE Std 802.6) network is addressed, and several alternative solutions that can improve the network's fairness are proposed. Implementation methods that require simple additional hardware on top of the regular DQDB interface are outlined. Simulation examples are employed to compare the performance of the schemes and to gain insight into their characteristics. The performance is also compared with that of the original DQDB and the bandwidth-balancing DQDB. An analytical model of the DQDB network is developed. Some constrained assumptions for analytical tractability are used to obtain a Markov chain model for (an earlier version of) the entire DQDB network, the corresponding state-space explosion problem is highlighted. For reasonably small systems, the analytical model can predict an individual station's throughput and mean segment delay for known (possibly asymmetric) loading patterns. The model is verified via simulation.>

The goal of the study described is to exploit the capabilities of emerging lightwave technology and the fact that the IEEE 802.6 MAN is a linear network, to construct near optimal linear multihop lightwave networks. Heuristic algorithms are proposed for constructing photonic implementations of near optimal distributed queue dual bus (DQDB) structures. Two sets of heuristic optimization algorithms are formulated. The first set is concerned with minimizing the maximum flow in any link in the network, while the second set of heuristics is aimed at minimizing the network-wide mean packet delay. Important properties of these algorithms are analyzed and their performance is demonstrated with several representative numerical examples.>

This study deals with the distributed queue dual bus (DQDB) (IEEE 802.6) network, and makes two independent contributions. First, the unfairness problem of DQDB is addressed, and several alternative solutions that can improve the network's fairness are proposed. They include (1) the proportional assignment scheme (PR); (2) the (multiple-request) FCFS (first come first served)-message-queue-based DQDB scheme (MD); and (3) a combination of MD and PR, denoted by MP. Implementation methods that require simple hardware in addition to the regular DQDB interface are outlined. The schemes are compared through simulation, and insights into their characteristics are gained. The performance of these schemes is also compared with that of regular DQDB and bandwidth balancing DQDB. The second contribution is the development of an analytical model of the DQDB network. By employing some constrained assumptions for analytical tractability, a Markov chain model for (an earlier version of) the entire DQDB network is formulated. The model is verified via simulation.>

The p/sub i/-persistent protocol is based on a probabilistic scheduling mechanism (see Mukherjee and Meditch, 1988). The authors further develop the protocol to make it easily implementable, by allowing it to be sensitive to changing load conditions. They study various properties of a simple algorithm which stations execute independently by using channel feedback information. This results in a fully distributed control mechanism that continuously adjusts the station probabilities p/sub i/ at their proper levels as governed by the offered traffic. An extensive simulation model has been developed to study properties of this control mechanism such as p/sub i/ settling time and accuracy, behavior under step changes in traffic load, effect of injection of additional packets, and effect of various parameters associated with the underlying algorithm. These experiments indicate that this algorithm is suitable for implementing the protocol.>