To Total Harmonic Distortion Research Articles

A Comparative Study of Different Control Algorithm Used in Unified Power Quality Conditioner (UPQC) for Power Quality (PQ) Improvement

Demand for power is on constant increase and it has necessitated the use of alternative energy sources that are discrete in nature and need conversion for utilisation. For this conversion, use of the semiconductor devices is indispensable, which has its own technical challenges and one among them is power quality (PQ). PQ has gained a widespread attention with the increase in penetration level of distributed generation (DG). Integration of DG sources in the grid introduces PQ issues like harmonics, flickers, voltage swells and sags in the system. Unified power quality conditioner (UPQC) is identified to be a reliable and efficient flexible AC transmission systems (FACTS) controller to mitigate the power quality problems. UPQC is based on a hybrid technology that consists of series and shunt inverters connected via a DC link that provide voltage compensation and current compensation. Characteristics of the UPQC are dependent on embedded control algorithm, which ensures proper voltage regulation at DC link and capacitor-voltage equalisation. This paper compares the control algorithms utilised in UPQC for generating reference signals for providing voltage and current compensation, with a special emphasis to total harmonic distortion (THD).

Synchronous Optimal Modulation: Frequency or Time Domain, Global or Constrained Optimization? 40 Years to the First Formulation

Alternative approaches to total harmonic distortion (THD) minimization comprise frequency or time domain THD calculations and global or constrained optimization problem formulation. Time domain constrained optimization formulation suggested in 1977 that seems most adequate from computational efficiency and robustness does not attract sufficient attention it deserves from the modern researchers. Time domain current THD/harmonic loss constrained optimization is illustrated by single-phase inverter examples. New results on multilevel THD optimization for variable voltage levels are presented.

An improved synchronous reference frame current control strategy for a photovoltaic grid-connected inverter under unbalanced and nonlinear load conditions.

In recent years, renewable energy sources have been considered the most encouraging resources for grid and off-grid power generation. This paper presents an improved current control strategy for a three-phase photovoltaic grid-connected inverter (GCI) under unbalanced and nonlinear load conditions. It is challenging to suppress the harmonic content in the output current below a pre-set value in the GCI. It is also difficult to compensate for unbalanced loads even when the grid is under disruption due to total harmonic distortion (THD) and unbalanced loads. The primary advantage and objective of this method is to effectively compensate for the harmonic current content of the grid current and microgrid without the use of any compensation devices, such as active and passive filters. This method leads to a very low THD in both the GCI currents and the current exchanged with the grid. The control approach is designed to control the active and reactive power and harmonic current compensation, and it also corrects the system unbalance. The proposed control method features the synchronous reference frame (SRF) method. Simulation results are presented to demonstrate the effective performance of the proposed method.

Analysis of various control schemes for minimal Total Harmonic Distortion in cascaded H-bridge multilevel inverter

Multilevel inverters are becoming more popular in the power conversion systems for high power and power quality demanding applications. The MATLAB based simulation on SIMULINK platform is presented for the Single Phase five level cascaded H-bridge Multilevel Inverter (CHB-MLI) topology with less number of switches and with different control schemes and Sinusoidal Pulse Width Modulation (SPWM) schemes. A detailed comparison of various control schemes is presented in this paper with reference to Total Harmonic Distortion (THD) in the output voltage and utilization factor of the power devices. It is observed that among all the control schemes, the THD is minimum in the Sinusoidal Pulse Width Modulation-Phase Disposition (SPWM-PD) scheme with variable carrier wave magnitude.

Comparative Analysis of Three-Phase AC-DC Converters Using HIL-Simulation

This paper presents a comparative evaluation of various topologies for three-phase power converters using the hardware-in-the-loop (HIL) simulation technique. Various switch-mode AC-DC power converters are studied, and their performance with respect to total harmonic distortion (THD), efficiency, power factor and losses are analyzed. The HIL-simulation is implemented in an Altera Cyclone II DE2 Field Programmable Gate Array (FPGA) Board and in the Matlab/Simulink environment. A comparison of the simulation and HIL-simulation results is also provided.

Analysis of total harmonic distortion in microspeakers considering coupling effect

With the advent of the mobile phone, Digital Multimedia Broadcasting (DMB) service for multimedia data communication will soon be realized. With regard to the acoustic aspects of this service, a smaller and lighter microspeaker also soon will be implemented in MP3 song players and speakerphones. The sound quality of such microspeakers, as evaluated with reference to total harmonic distortion (THD) is becoming more important. THD is the proportion of the higher-order frequency output response to a sinusoidal input signal. It is affected by uneven magnetic distribution and nonlinear responses of diaphragms. In this work, THD was analyzed in consideration of the coupling effects between mechanical vibration and electromagnetic exciting forces. Simulated THD results were compared with the experimental data. The THD in the lower frequency range increased due to the increased displacement of the voice coil and the elevated high-order component response of the sound pressure.

Four-wire dynamic voltage restorer based on a three-dimensional voltage space vector PWM algorithm

A modified voltage space vector pulse-width modulated (PWM) algorithm for a four-wire dynamic voltage restorer (DVR) is described. The switching strategy based on a three-dimensional (3-D) /spl alpha//spl beta/O voltage space is applicable to the control of three-phase four-wire inverter systems such as the split-capacitor PWM inverter and the four-leg PWM inverter. In contrast to the conventional voltage space vector PWM method, it controls positive, negative and zero sequence components of the terminal voltages instantaneously. Three 3-D modulation schemes are analyzed with respect to total harmonic distortion (THD), weighted total harmonic distortion (WTHD), neutral line ripple and switching loss over the whole range of the modulation index when the DVR experiences both balanced and unbalanced sags with phase angle jumps. Experimental results from a 9 kW DVR system using a split-capacitor PWM inverter are presented to validate the simulation results.