B. Kalyan Kumar

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.

Particle Swarm Optimization-Based Feedback Controller for Unified Power-Quality Conditioner

The unified power-quality conditioner (UPQC) is used to provide balanced and sinusoidal source currents and load voltages under unbalanced and distorted three-phase supply voltages and load currents in a power distribution network. In this paper, a particle swarm optimization-based feedback controller is designed for UPQC. This feedback controller has optimal performance in various operating conditions and is robust to parametric uncertainties when compared to the conventional feedback controllers, such as the linear quadratic regulator. The proposed method is implemented on a distribution system and detailed simulation and experimental results are presented.

Rating and design issues of DVR injection transformer

The load side voltage disturbances can be effectively mitigated by connecting a dynamic voltage restorer (DVR), a series compensating device. A DVR is realised by a voltage source inverter with DC storage device and a series injection transformer. Rating and design issues of an injection transformer are of prime concern for the proper voltage compensation using DVR. Voltage underrating of the transformer may lead to its saturation, whereas, overrating increases the cost and size of the DVR. The voltage applied to the primary winding of the transformer is a combination of several components of different frequencies. Considering above aspects, rating and design issues are presented in this paper. A novel method is proposed to find the voltage rating of the transformer as a function of the fundamental frequency. Furthermore, the inrush current due to saturation is avoided during transient period. K factor method is used to account for the effects of current harmonics in the transformer. A PSCAD model is used...

Minimization of VA loading of Unified Power Quality Conditioner (UPQC)

The Unified Power Quality Conditioner (UPQC) is a versatile device which could function as series active filter and shunt active filter. UPQC can simultaneously fulfill different objectives like, maintaining a balanced sinusoidal (harmonic free) nominal voltage at the load bus, eliminating harmonics in the source currents, load balancing and power factor correction. Keeping the cost effectiveness of UPQC, it is desirable to have a minimum VA loading of the UPQC, for a given system without compromising compensation capability. Hence, a methodology has been proposed in this work to minimize VA loading of UPQC considering the effects of source voltage and load current distortion. The series active filter of UPQC can be made to inject voltages in such a way that a minimum VA loading of UPQC is possible. The optimal angle at which series voltage has to be injected so as to have minimum VA loading of UPQC is computed by Particle Swarm Optimization (PSO) technique. The proposed method has been validated through detailed simulation studies. The VA loading without optimization and with optimization has been compared.

Optimal VA loading of UPQC during mitigation of unbalanced voltage sags with phase jumps in three-phase four-wire distribution system

In this paper, a new methodology is proposed to mitigate the unbalanced voltage sag with phase jumps by Unified Power Quality Conditioner (UPQC). UPQC is used to mitigate both voltage and current power quality (PQ) problems. During the process of mitigation, UPQC is supposed to inject real and reactive power into the system to mitigate current (shunt) and voltage (series) power quality (PQ) problems. As per the sensitive load concerns, deep and long duration sags are more vulnerable than shallow and short duration sags. To resolve these issues a new methodology is proposed with optimal Volt-Ampere (VA) loading on UPQC to mitigate deep and long duration unbalanced sag with phase jumps. Particle Swarm Optimization (PSO) is utilized as a tool for evaluating the optimal VA loading of UPQC with constraints like magnitude of injected voltage from Series active power filter, Total Harmonic Distortion (THD) of source current and terminal voltage. The proposed methodology ensures optimal VA loading on UPQC without compromising mitigation capability of the UPQC. The proposed method has been validated through detailed simulation studies.

Power quality survey in a technological institute

This paper discusses the power quality survey conducted in the distribution system of Indian Institute of Technology Madras, Chennai, India. Individual power quality parameters measured from the survey are analyzed and presented in detail. To assess the power quality, measured data are compared with various power quality standards including IEEE 519-1992 standard for the measured voltage and current harmonics. The information obtained from this survey will be useful in improving the quality of power in the Institute.

Compensation of voltage sags and harmonics with phase-jumps through DVR with minimum VA rating using Particle Swarm Optimization

Dynamic Voltage Restorer (DVR) restores the distribution system load voltage to a nominal balanced sinusoidal voltage, when the source voltage has distortions, sag/swell and unbalances. DVR has to inject required amount of Volt-Amperes (VA) into the system in order to maintain a nominal balanced sinusoidal voltage at the load. A new control technique is applied to compensate the sag and harmonics with phase jumps in the source voltages. Keeping the cost effectiveness of DVR, it is desirable to have a minimum VA rating of the DVR, for a given system without compromising compensation capability. Hence, a methodology has been proposed in this work to minimize VA rating of DVR. The optimal angle at which DVR voltage has to be injected in series to the line impedance so as to have minimum VA rating of DVR as well as the removal of phase jumps in the three-phases is computed by Particle Swarm Optimization (PSO) technique. The present method was able to compensate voltage harmonics and sags with phase jumps by keeping the DVR voltage and power ratings minimum, effectively. The proposed method has been validated through detailed simulation studies.

Identification of Inter-Area Oscillations Using Zolotarev Polynomial Based Filter Bank With Eigen Realization Algorithm

Inter-area oscillations in power systems needs to be monitored and accurate estimation of frequency and damping of the oscillations in real time is vital as they provide considerable insight into system stability. Zolotarev polynomial based filter bank (ZPBFB) is proposed for decomposing the PMU signals into monocomponents. Modal frequency and damping are obtained from the decomposed monocomponent signals through eigen realization algorithm (ERA). The salient property of ZPBFB lies in signal decomposition with sum of decomposed signals produced by filter bank, without oversampling, is an exact replica of input signal with delay. A narrow bandwidth of 0.1 Hz is achieved in the frequency range of 0 to 1 Hz with ZPBFB. The robustness of the proposed method to noise is demonstrated using Monte Carlo simulations. The proposed ZPBFB and cosine modulated filter bank (CMFB) are implemented on two-area test system and 16-machine, 68-bus system and the performances are compared. The efficacy of the proposed method is also demonstrated on three real time signals recorded by wide area frequency measurement system (WAFMS) at 3 locations in India on November 30, 2011.

Effect of Modeling of Induction Generator Based Wind Generating Systems on Determining CCT

Transient stability of wind generation system is evaluated in terms of critical clearing time (CCT) of fault. CCT of a wind generation system connected to grid is calculated based on the maximum amount of time that the wind generation system remains connected to grid, without becoming unstable, when the grid is subjected to a fault. In the literature, the wind turbine model has been used for steady state analysis alone, that is, it is used for finding the initial operating mechanical torque output of the turbine. The turbine model is then completely neglected in case of transient stability analysis by assuming constant mechanical torque output for a particular wind speed. This may not be true, as the mechanical torque-speed characteristic of a wind turbine depends not only on the wind speed but also on the slip of the induction generator connected to the wind turbine. This paper explains the necessity of considering the wind turbine model for the transient stability and steady state analysis of grid connected induction generator based wind generation system. A detailed analysis has been done on the effect of various electrical and mechanical factors on CCT determination and the simulation results are presented.

Complex wavelet based control strategy for UPQC

This paper discusses the utilization of complex continuous wavelet transform based on B-spline function for reference voltages and currents extraction which are used for compensating power quality disturbances by using unified power quality conditioner. The major advantages of choosing B-spline function are the reduction of computation time and ease of online implementation. The performance of the proposed wavelet transform is compared with the discrete Meyer wavelet and complex Morlet wavelet transforms. Detailed simulation studies are carried out using Matlab/Simulink to prove the ability of the proposed method. It is inferred from the simulation results that the proposed B-spline complex wavelet transform based reference signal extraction is as accurate as complex Morlet wavelet transform but has less computational burden.