This paper establishes the fact that optimum value of firing angle for the thyristorized voltage controller fed induction motor at starting depends on motor parameters. Identically rated motors with different parameter values are considered for the work. Extensive simulations are carried out to obtain the optimum firing angle of the voltage controller, which gives zero negative torque pulsations with minimum acceleration time. Other factors under considerations are peak positive electromagnetic torque pulsations, peak starting current, nature of the voltage and current waveforms at steady state and current ripple. Results show that, though the machines have same rating, their optimum firing angles are different due to the difference in parameters.
Performance evaluation of an isolated wind/hydro electric generation scheme having variable speed 3-phase Self Excited Induction Generator (SEIG) operating in synchronism with a Generalized Impedance Controller (GIC) has been presented in this paper. The GIC is an impedance controlled operation of Pulse-width-modulated voltage source inverter (PWM-VSI). The performance of the SEIG-GIC integrated synchronized operation under open loop condition, with fixed excitation and balanced isolated load, has been analyzed in detail for variations in modulation index ‘m’ of the GIC and relative phase angle ‘δ’ between the fundamental components of the GIC and the SEIG terminal voltages. The GIC operation is controlled by implementing Space Vector Pulse Width Modulation (SVPWM) technique. Detailed experimental studies have been undertaken on a laboratory prototype of the SEIG-GIC system for steady state operation. The effects of variations in ‘m’ and ‘δ’ on the amplitude and frequency of the SEIG terminal voltage and active and reactive power flow between the SEIG and the GIC are presented here.
Air-gap eccentricity is a fault that mainly affects large induction motors. In the worst case an eccentricity fault can result in a stator rotor rub thereby causing severe damage to the motor. As a result eccentricity fault detection has gained considerable significance. Of all detection schemes for this fault, Motor Current Signature Analysis (MCSA) is the most widely used technique. This scheme relies on identifying fault specific frequency component in the line current spectrum of the motor to identify the type of fault. The severity of the fault can be estimated by monitoring the magnitude of the characteristic frequency component. To characterize the fault severity an accurate model of induction motor has to be developed. Two models - Finite Element(FE) based model and Modified Winding Function Approach (MWFA) based model are used in this paper to estimate the magnitude of fault specific frequency components for different eccentricities at full load condition. The results obtained from the two methods are compared to find the suitability of MWFA based model in characterizing the fault severity.
The time of operation of overcurrent relays (OCRs) can be reduced, and at the same time coordination can be maintained, by selecting the optimum values of time multiplier setting (TMS) and plug setting (PS) of OCRs. This paper presents formulation of the problem of determining optimum values of TMS and PS of OCRs as a constrained nonlinear optimization problem, and solution of the same using big-M (penalty) method, which is a method used to find optimum solution of linear programming problem (LPP). The method introduces artificial variables in the objective function to get an initial basic feasible solution (IBFS). Artificial variables are removed using iterative process which also leads to an optimum solution.
Proportional Integral Derivative (PID) controller is the most preferable controller in industries that does not require precise analytical model of the system to be controlled. This paper presents a design and implementation of PID (Proportional-Integral-Derivative) controller based on FPGA (Field-Programmable Gate Arrays) for low voltage synchronous buck Converter. Matlab/Simulink environment is used for the PID controller design to generate a set of coefficients associated with the desired controller characteristics. These controller coefficients are then included in VHDL that implements the PID controller on to FPGA. The two architectures of PID controller are considered with their device utilization and power dissipation reports to show the resource utilization and power dissipation of selected FPGA. The architectures are implemented in FPGA Virtex-5(ML505) XC5VLX50T-1FF1136 (-1 speed grade) device.
This paper deals with dynamic performance of wind diesel system with variable wind speed turbine. The quality of power supplied to the autonomous system is improved by controlling the frequency to the rated value. To improve the system characteristics, a variable speed operative wind generator: Doubly-Fed Induction Generator along with diesel generator in the isolated hybrid system is used. The simulation results of the proposed hybrid system are presented to demonstrate its effectiveness in meeting change in load demands along with change in wind speed. The system is also studied for a short circuit fault to ensure the stability. The performance of the proposed system is analyzed using MATLAB/SIMULINK and it is found that the fluctuations in power and frequency are minimum.
Four-level inversion is realised by connecting two two-level inverters, fed from both ends of open-end winding induction motor with Asymmetrical DC link voltages in the ratio of 2:1. This inverter scheme produces 64 space-vector combinations distributed over 37 space-vector locations. All the switching combinations are not helpful to achieve four level inversion, some of the combinations overcharge DC-link capacitor of the inverter operating with a lower DC-link voltage of Vdc/3 by other inverter with higher DC-link voltage of 2Vdc/3. Decoupled space vector PWM switching strategy is described to eliminate the overcharging effect. Isolated DC power supplies are employed to avoid the zero-sequence currents. Simulation and experimental results are presented in this paper.
This paper illustrates the implementation of the direct torque control (DTC) strategy for induction motor (IM) drive using carrier space vector pulse width modulation technique. In the present work, the algorithm used for DTC based control of IM is Carrier Space Vector Pulse Width Modulation (CSVPWM) technique. A comparison of performance between standard and carrier based SVPWM techniques have been made considering the presence of harmonics in phase voltage, phase current and stator flux linkage which are responsible for the torque ripple. Using simulation results relative merits of the standard SVPWM (SSVPWM) and CSVPWM have been evaluated. Overall performance of conventional, SSVPWM and CSVPWM DTC based IM drive from the viewpoint of torque ripple minimization have been evaluated using simulation results. Simulation results are experimentally validated.
This paper proposes a simple harmonic feedback strategy for reduction of output voltage harmonics and the removal of any voltage unbalance due to unbalanced linear and non-linear loads in three-phase inverters. The fundamental components of the voltage and current are controlled in dq frame. Two-phase observers have been used for estimating the fundamental αβ components of the inverter voltage and the load current, which in turn helps to segregate the harmonics from the signal. The observer based control strategy, reduction of harmonic distortion and load voltage balancing by the simple harmonic feedback approach has been verified by simulation and experiments.
This paper presents the voltage build-up process and the terminal voltage control of a stand-alone self-excited induction generator (SEIG) using direct vector control (DVC) technique under variable speeds and different types of load. Here, the three-phase SEIG is excited by a pulse-width modulated voltage source inverter (PWM-VSI) connected to a single-capacitor on the DC side with a start-up battery. The limitation of having stand-alone SEIG is poor voltage regulation, which occurs with change in speed and load condition. Hence, there should be a control system that keeps the terminal voltage of the SEIG and the DC bus voltage constant when the speed of the rotor and also, the load on the SEIG are varied. The direct vector control scheme has been presented to maintain the terminal voltage of the generator and the DC bus voltage constant for variable rotor speed and load. The space-phasor model of the induction machine has been used in simulation. To predict the performance of the proposed system, a MATLAB/SIMULINK based study has been carried out for both AC and DC loads. The proposed control scheme has shown very good voltage regulation and phase balance even with unbalanced three-phase load.
A new seven-level inverter topology for IM drive is proposed in this paper. This topology consists of two three-phase two-level inverters fed by isolated DC voltage sources and six H-bridges fed by capacitors. An important advantage of this topology is the reduction in DC link voltage magnitude by half when compared with the requirement of DC link voltage in conventional NPC or flying capacitor topologies. The switching state redundancies that exist in generating the middle voltage levels are effectively utilized in balancing the H-bridge capacitor voltages. The proposed topology is inherently capable of preventing the circulation of triplen harmonic current caused by the common mode voltage appearing on the motor winding. Another feature that enhances the reliability of the proposed drive system is its ability to function in three-level mode in case of any switch failure in H-bridges. Extensive simulation study and experimental verification of the proposed topology are carried out for the entire modulation range.
This paper describes the novel design and optimization of an axial flux motor for blood pump application. With the design objective of maximizing the motor efficiency, different topologies of AFPM machine has been examined. Halbach arrangement of rotor magnets and use of Soft Magnetic Composite (SMC) material for the stator core adds further advantages to the optimal motor design. The results of the 3D Finite element analysis for the novel motor have been shown.
The effectiveness of a Thyristor Controlled Series Capacitor Power Oscillation Damping controller (TCSC PODC) in enhancing the power system dynamic performance of a fundamental power system model is explored in this paper. Controller parameters are optimally tuned using Genetic Algorithm (GA) to achieve better dynamic performance. A multi-objective problem is formulated to optimize a composite set of objective functions comprising damping factor and damping ratio of critical eigenvalues in and around the Hopf bifurcation point. The generator and its excitation control dynamics are modelled by four first-order differential equations. It is shown that when excitation control gains are set high and when the excitation hard-limits are taken into account, the fundamental power system model undergoes global bifurcations including period-doubling cascades, which lead to sustained chaotic behaviour. The route of cascading period-doubling bifurcation (PDB) is deeply studied and PDB route to chaos is presented. The existence of the chaos, also called strange attractor, is confirmed by time domain plots and phase plots. The simulation results show that the GA tuned TCSC PODC is effective in mitigating the chaotic electromechanical oscillations and hence effective in enhancing the power system dynamic performance.
In this paper, a novel control algorithm for three-phase four-wire shunt active power filter for the compensation of instantaneous harmonic current components in nonlinear loads is presented. Fundamental signal extraction is carried out using Harmonic Tuned Filter (HTF) without the Phase Locked Loop (PLL). HTF can efficiently determine the fundamental signal components from distorted voltage or current signal. Instantaneous Reactive Power Theory (IRPT) is used for reference current signal generation. The net fundamental power is calculated by using control architecture which should be flow from source to load. Indirect current control technique is used for the generation of switching signals. After providing compensation by APF, supply voltage and current are nearly in-phase which indicates power-factor improvement. The control technique is first simulated in MATLAB/Simulink environment and then co-simulated using processor-in-loop (PIL) technique on TMS320F28335 floating point digital signal processor. THD and PIL response prove that active filter is able to bring % THD with-in limits and as per IEEE 519-1992 standard limits.
Biogeography-Based Optimization (BBO) is a recently developed global optimization algorithm and has shown its ability to solve complex optimization problem. The convergence of original BBO to the optimum value is slow as it lacks the exploration ability. An Accelerated Biogeography-Based Optimization (ABBO) technique is proposed in this paper to solve economic load dispatch problem. In this paper, the performance of the original BBO is accelerated so at to enhance the exploitation and exploration ability by introducing a modified mutation operator and clear duplicate operator. This significantly improves the convergence characteristics of the original algorithm.
Wholesale power markets operating over transmission grids subject to congestion have distinctive features that complicate the detection of market power and operational inefficiency. In this paper, an engineering procedure is proposed for a given pattern of dispatch to measure the potential for market power for all generators in a network. This procedure is equivalent to a set of factor demand equations in a standard neoclassical model of production. An optimal dispatch, for given sets of offers to sell and constraints on capacity, can be replicated exactly by resolving the dispatch using the optimal nodal prices as offers with no constraints on capacity. Market power exists when the degree of substitutability for power generated at a particular site is low. Withholding capacity and/or raising offers to sell at such a site would be one of the possible ways to exploit market power. Examined measures include the Herfindahl-Hirschman Index (HHI), the Lerner Index (LI), Generator Market Share (GMS), Must Run Ratio (MRR) and relative market power (RMP). The model has been applied on an IEEE 30 bus system, six of which are Generators using MATPOWER, which simulates a full AC network.
Steady state analysis of single-phase self excited induction generator is almost always carried out using the concepts of symmetrical components and the rotating field theories. The machine is modeled through its positive and negative sequence circuits with appropriate parameters pertaining to forward and backward fields. The final expression obtained through these analyses is a complex nonlinear equation with magnetizing reactance and frequency as two unknown quantities. Once the equation is solved and the values of magnetizing reactance and frequency precisely evaluated, the analysis of the machine performance becomes straight forward. This paper presents the use of “fsolve” optimization tool of Matlab in solving this complex equation yielding magnetizing reactance and frequency which, finally helps in the complete steady state analysis of the single-phase self excited induction generator. The method is found to be elegant and user-friendly.
This paper describes the implementation of multirate sampling technique for carrier space vector pulse width modulation based direct torque control (CSVPWM DTC) of induction motor (IM) drive with an objective to reduce the electromagnetic torque ripple. The benefit of the proposed technique for CSVPWM DTC based IM drive; it gives lower torque ripple as compared to single rate sampling technique. In multirate sampling technique, for the same digital signal processor, two sampling periods are used. The fundamental sampling period which is smaller than the sampling period used in single rate sampling technique, is used for data capturing and estimation of speed, torque and flux parameters. The other sampling period which is an integer multiple of the fundamental sampling period, is used for speed, flux and torque error processing and also for the implementation of CSVPWM algorithm for synthesizing gate pulses. Further, due to lower fundamental sampling period in multirate sampling technique better resolution in switching pulse widths can be obtained. Using simulation results relative merits of the multirate and single rate control strategy have been evaluated from the viewpoint of torque ripple minimization. The simulation results are experimentally validated.
This paper focuses on the effective utilization of Flexible AC Transmission System (FACTS) and High Voltage Direct Current (HVDC) interconnection link for the improvement of voltage profile, stability and loss allocation in heavily loaded as well as contingent conditions of the network. The weakest bus interconnection has been replaced by FACTS and HVDC link and a study has been carried out to prove their effectiveness in an interconnecting network under deregulated environment. The IEEE 14 bus system, operating with common loads and generators is used to demonstrate the usefulness of FACTS and HVDC link. A new voltage stability index (VSI) has been proposed in this paper for stability analysis with HVDC and FACTS. A comparative analysis between FACTS and HVDC has also been presented in this paper, for their comparison, in field of power quality and cost efficiency.
This paper presents the dynamic modeling and simulation of a feedback linearization scheme for high performance induction motor control which decouples the rotor flux and the rotor speed (torque) control loop. In this scheme the controller takes rotor flux from the feedback path and uses it for the cancellation of nonlinearity present in the rotor flux and the rotor speed control signal. As direct flux measurement is proved not to be suitable due to the need of sensor and the sensor in itself sensitive to temperature. The scheme uses a flux estimator. Furthermore the process is implemented on the stationary reference frame. This offers less complex method than the Vector Control Scheme where the requirement for the precise knowledge of the instantaneous position of space flux and the transformation of a synchronous coordinates system into a structure of stationary reference frame and vice-versa makes the system more complex. Like vector control it uses PI controller for speed and flux. To confront the problem of uncertainties fuzzy controller is used. The control scheme is simulated in MATLAB environment. Simulation result demonstrates good performance and makes it fair competitive to the other high performance schemes of Induction motor.
