Band 13, Heft 2

The brushless DC motor (BLDC motor) drive is used in several high performance applications ranging from servos to traction drives, due to several distinct advantages such as high power density, high efficiency, fast response and maintenance free. BLDC motor is usually driven by hard switching PWM inverter, which normally has higher switching losses. In recent years, these are several soft switching inverters presented. But there are many disadvantages such as high device voltage stress and large DC link voltage ripple and so on. This paper presents a transformer based resonant dc link inverter for brushless dc motor. The modulation strategies can be classified into two kinds according to the turn-off sequence of the two switches of the pair of switches. Here, dc link voltage notches during chopping switches commutation for all switches working in zero voltage switching condition. The operating principle of soft switching and control scheme are presented. The proposed scheme is verified with the simulation and experimental results.

This paper establishes a new method that adopts the line-flow-based (LFB) approach to develop a transient stability constrained optimal power flow (OPF) analysis called LFB-TSCOPF. The transient energy function (TEF) serves as a direct means of carrying out the stability analysis. The reduction technique was adopted in which the classical machine model was reduced to the internal node model. The proposed method was tested on the WECC 9-bus, three-machine, IEEE 14-bus, five-machine, and the New England 39-bus, ten-machine test systems. The results were compared with other known results from different methods in literature. The results of the active power and total optimal costs are quite promising and consistent with other known methods. The LFB-TSCOPF re-dispatches real power by applying the energy margin performance index as an indication of the generator unit(s) to be rescheduled. The LFB-TSCOPF provides a more comprehensive linear model, reduces computation time and can be useful for online stability studies.

Distributed Generation “DG” is an emerging technology which is receiving mush attention and studies. One of the most important aspects of DG is reliability. Reliability is defined as the ability of the system to deliver electrical power to the customers within various limits. These limits include limits on continuity of supply, voltage drop, sag, regulation and other limits which are mentioned in various standards. This paper focuses on solving some problems with the reliability modeling of DGs [1]. Existing algorithms which deal with DG are very complex due to the nature of the model of the DG itself [1]. Some of the protection algorithms have to be complex so that they do not to count the DG twice [2]. In this paper protection algorithms and set of equations are proposed to accurately model the DG and calculate its effect on Load point indices. Then the method is applied to a study case to illustrate the steps needed to calculate the load point indices [3]. A load flow result will be used to determine the size of the DG needed. The system which will be studied is a system where the DG serves an island or what is known as islanded operation of DG [4]. The method only applies to islanded operation and cannot be used for other modes of operation of the DG. The results show that a very accurate method could be used to model the DG without the need for complex, time consuming algorithms which a characteristic of the existing algorithms. This paper presents the role of the DG in improving the system reliability by proposing a new method for calculation of load point indices in the case of DG presence in the system. The method is then applied to a study case.

System islanding is often considered as the final stage of power system defense plans. The goal is to preserve stable areas of the faulted power systems. The islanding scheme plays an important role in the power system restoration phase as it can make the power system restoration less complex and reduce the overall restoration time. The basis for islanding is not standard but rather depends upon the nature of the utility. Even though the formation of islands is dominated by geographical proximity of the synchronous generators to maintain generation-load balance, there are some factors which can assist in designing a better islanding scheme. These factors are the type and location of the fault and the dynamic performance of every island on the system against the fault. This paper present the application of islanding scheme and its performance operation for the scheme commissioned at 132 kV Deepnagar Bhusawal Thermal Power Station (BTPS). The methods and constraints of islanding scheme are discussed in details. Case studies regarding performance of islanding scheme are also described.

Damping of low-frequency electro-mechanical oscillations is essential for reliable operation of power systems. The fast acting, power electronics based FACTS controllers which are capable of improving both steady state and dynamic performance permit enhanced approaches to system stabilization. This paper presents the control laws and location index proposed for a static synchronous compensator (STATCOM) based on a circuit analogy of the electro-mechanical system. The signals which are used can be synthesized using locally available measurements. A detailed study of small signal analysis is carried out to study the effectiveness of the control law and strategic location of the damping controller. With the objective of damping oscillations, a nonlinear constrained optimization technique has been presented for tuning the controller parameters with and without phase compensation. Transient stability analysis has then been performed with STATCOM for a multimachine power system. Comparison of the optimization technique with that of the classical root locus method shows improvement of stability obtained with the former. Case studies on a single machine infinite bus system, three machine system and ten machine systems illustrate the effect of STATCOM on transient stability and its accurate prediction.

This paper is to propose an optimization method that searches for the optimal installed capacity of wind turbines (WTs) in smart grids from the perspectives of both WTs developers and distribution network operator (DNO). The proposed hybrid optimization method combines the genetic algorithm and the multi-period optimal power flow analysis. The objective of the optimization is to maximize the net present value of the profits obtained by the WTs developers as well as that of the savings obtained by the DNO from network loss reduction. A 69 bus 11 kV radial distribution network is used as a case study to demonstrate the proposed algorithm, with the implementation of different active management schemes. Simulation results show that the optimal WT capacity from the perspective of DNO differs from the optimal value deemed by the WT developers. The resulting economic benefits can be used by both DNO and WT developers to justify an increase in WT installation if desired. The two contrasting schemes see either the WTs developers or DNO benefiting at the expense of the other. As such, using tradeoff analysis it may be possible to find suitable compromises.

This paper presents a novel Digital Signal Processor (DSP) based control algorithm for 3-phase shunt active power filter (APF) using neural network and indirect current control strategy to eliminate current harmonics and reactive power compensation under ideal and distorted supply voltage. The compensation process is based on sensing of source current instead of filter current, and thus differs from conventional techniques for elimination of switching ripples. Fundamental frequency signal extraction is done using adaptive linear neuron (ADALINE) network from distorted voltage signal without using low-pass filter or phase-locked-loop block. ADALINE gives simple, robust and accurate design for selected frequency extraction. Instead of calculating oscillating and reactive power, the reference generation is used to calculate average active power component. Various simulation results are presented to study the performance of proposed design during steady-state and transient conditions of non-linear loads using MATLAB/ Simulink tool under sinusoidal and distorted supply voltage conditions. Simulated response has been validated with a laboratory prototype using a Texas make floating-point TMS320F28335 DSP. Based on the simulated and experimental results it can be concluded that the spectral performance of the input current are in compliance with the harmonic limits imposed by IEEE-519 standard.