D. V. S. S. Siva Sarma

Wavelet transform based harmonic analysis and real power measurement

This paper proposes a method of harmonics detection and theoretical basis for the measurement of reactive and distortion powers using wavelet multi-resolution technique. The proposed method decomposes the voltage/current waveforms into the uniform frequency bands corresponding to the odd-harmonic components of the signal and uses a method to reduce the spectral leakage due to the imperfect frequency response of the used wavelet filter bank. The harmonic analysis has been performed on typical distribution system and compares the performance of the proposed method with the results obtained using the discrete Fourier transform (DFT) analysis. The measurement of real power relies on the use of broad-band phase-shift networks to create concurrent in-phase currents and quadrature voltages. The advantage of viewing the real and reactive powers in the wavelet domain is that the domain preserves both the frequency and time relationship of these powers. The harmonic analysis and real power measurement in a typical distribution system using wavelet multi-resolution technique is verified in MATLAB/SIMULINK environment.

Application problem of PWM AC drives due to long cable length and high dv/dt

Advances in power electronics technology have improved the performance and output waveforms of PWM voltage source inverters. Switching frequencies of 2 to 15 kHz with 0.1 mus rise times are common with the current IGBT technology while allowing for power levels over 200 kW. While the high switching speeds and zero switching loss schemes drastically improve the performance of the PWM inverters, the high rate of voltage rise (dv/dt) of 0 to 600 V in less than 0.1 mus has adverse effects on the motor insulation and bearings and deteriorates the waveform quality. Long cables contribute to a damped high frequency ringing due to the distributed nature of the cable leakage inductance and coupling capacitance (L-C) at the motor terminals resulting in over voltages which further stress the motor insulation. Voltage reflection is a function of inverter output pulse rise time and the length of the motor cables, which behave as a transmission line for the inverter output pulses.

Classification of voltage sag, swell and harmonics using S-transform based modular neural network

This paper presents classification and characterization of typical voltage disturbances- sag, swell, interruption and harmonics employing S-transform analysis combined with modular neural network. S-transform is used to extract various features of disturbance signal as it has excellent time-frequency resolution characteristics and ability to detect disturbance correctly even in the presence of noise. Classification is performed using modular neural network with features extracted from S-transform. Modular neural network is designed by modifying the structure of traditional multilayer network into modules for each disturbance to provide less training period and better classification. Disturbances are characterized by magnitude and phase information using S-transform analysis. Simulation and experimental results show that S-transform combined with Modular neural network can effectively detect, classify and characterize the disturbances.

An improved SVPWM based shunt active power filter for compensation of power system harmonics

Space vector pulse width modulation (SVPWM) has been extensively utilized in the three-phase voltage source inverters (VSI) for the benefit of fixed switching frequency, full utilization of DC bus voltage and superior control. In recent times, SVPWM technique was applied for active power filter (APF) control application, as the APF is nothing but of a current controlled VSI. The conventional SVPWM based APF has high computational burden due to complex trigonometric calculations and sector identification involved to generate the compensating signal, hence the response time for compensation is slow. In this paper, an improved SVPWM technique based shunt APF is presented based on the effective time concept. The effective time concept eliminates the trigonometric calculations and sector identification, thereby it reduces the computational effort. Simulation results demonstrate the efficacy of the APF with the improved SVPWM based control strategy. The response time for compensation is 0.02sec.

Protection of distributed generation connected distribution system

This paper discusses some aspects related to the connection of distributed generators to radial distribution systems, especially their impact on the protection coordination. Penetration of a DG into an existing distribution system has many impacts on the system, with the power system protection being one of the major issues. The relays in the power system have to be coordinated so as to avoid mal-operation and unnecessary outage of healthy part of the system. In this paper, the Overcurrent relay coordination of simple radial industrial power plant is presented using NEPLAN Software. It presents the short circuit analysis of radial industrial power plant. This paper shows the star view of relays which is unique feature of NEPLAN for coordinating them correctly based up on recorded data of industrial distribution plant for calculating short circuit currents in industrial power system. Results obtained are verified by manual calculation.

Mitigation of Voltage Sag/Swell Using Peak Detector Based Pulse Width Modulation Switched Autotransformer

Abstract This article presents the fast detection of voltage sag/swell events by employing peak estimation of the signal. The algorithm used is very fast compared to event detection using root mean square calculation. A mitigation device with a pulse width modulation controlled autotransformer is employed for compensation of voltage sags/swells in a distribution system. This device does not require any energy storage device unlike mitigation devices employing DC-to-AC converter topology. Simulation results for mitigation of voltage sag due to faults/induction motor start and voltage swell due to capacitor switching show that nominal load voltage is achieved with a pulse width modulation switched autotransformer employing the peak estimation technique. The transient response of the device is about one cycle, and the total harmonic distortion of the load voltage is found to be within limits. A prototype model of a 230-V 2.5-kVA pulse width modulation switched autotransformer device is tested for mitigation of voltage sag/swell in an artificial transmission line system, and experimental results show that the device performance is satisfactory.

S-transform-based Hybrid Active Filter for Mitigation of Current Harmonics

Abstract This article presents a new control strategy for the hybrid active filter using S-transform. Frequency-domain analysis employing S-transform is used to extract the fundamental component of the non-linear load current. The switching patterns for the active filter are generated with pulse-width modulation. The proposed technique is simple and has better performance, even with low switching frequency, as compared to time-domain techniques. Simulation results are presented for steady-state and transient conditions, and the hybrid active filter is effective in maintaining the source current harmonics within the limits.

Three Level Hysteresis Current Controlled VSI for power injection and conditioning in grid connected solar PV systems

The penetration of solar Photo Voltaic (PV) systems to the grid is gradually being increased as an alternative to conventional energy sources. The interfacing of solar PV systems to the grid requires efficient control strategies for the operation, control and Power Quality (PQ) improvement. This paper proposes a three-level Hysteresis Current Control (HCC) strategy for grid connected four leg Voltage Source Inverter (VSI). The main objective of three-level HCC for VSI is to perform solar power injection as well as power conditioning such as compensation of harmonics, reactive power, neutral current and current imbalance. Conventional HCC suffers from variation in switching frequency, whereas the three-level HCC exhibits a considerable reduction in switching frequency variation by considering offset hysteresis band, thus enhances the control performance. Here a three phase four wire supply system connected to both linear and nonlinear unbalanced loads are considered. The efficacy of the proposed control concept is demonstrated with different operating conditions using MATLAB/Simulink© simulation studies.

Hysteresis current controlled active power filter for power quality improvement in three phase four wire electrical distribution system

Three-phase four-wire (3P4W) electrical distribution systems are extensively utilized in commercial and industrial sectors. These electrical distribution systems are facing severe power quality issues such as current harmonics, reactive power, and load unbalancing, excessive neutral current. This paper presents the analysis, design and digital simulation of a hysteresis current controller (HCC) based active power filter (APF) to improve the power quality in a 3P4W electrical distribution system. In the present work APF is implemented with a 4-leg voltage source inverter (VSI) which is connected in shunt to the 3P4W electrical distribution system. The VSI switching signals are generated through a hysteresis current controller (HCC), which has good current tracking accuracy, unconditioned stability and easy implementation. The proposed HCC based APF compensates current harmonics, reactive power, and load unbalancing and neutral current in 3P4W electric distribution system feeding nonlinear and unbalanced loads. The performance of the HCC based APF is demonstrated using MATLAB© simulation.

Implementation of Kalman filtering algorithm for Harmonic Load Impedance modelling of Electrical loads with Experimental Verification

The Power system disturbances like harmonics creates lot of power quality problems need to be analyzed with suitable analysis techniques. A simple technique has been presented in this paper for impedance load modelling of electric domestic loads like Geyser water heater system and Air conditioning System (AC). In this paper, the application of Kalman filtering algorithm is used for harmonic estimation and nonlinear load impedance modelling for validation of the algorithm. The Kalman filtering algorithm is used for harmonic estimation to the distorted current and voltage signals and also it will calculate the admittance or impedance for load impedance modelling to know the behavior of the system in presence of harmonics. The signal analysis methods like Fast Fourier transform (FFT), STFT, Wavelet transform and S-transform techniques are used to analyze the harmonics by using entire signal, but the proposed technique uses directly by taking one cycle samples of the voltage and current waveforms. It has been proved, that the proposed algorithm is verified with the PSCAD/EMTDC models as well as experimental results.