Additional Harmonic Losses Research Articles

COMPARATIVE STUDY OF TRADITIONAL PWM INVERTERS AND MULTILEVELS INVERTERS

The need of higher powers in electrical drives has forced the researchers to develop new power source possibilities. Multilevel inverters have been presented as a cost effective solution for various high voltage and high power applications including power quality and motor drive problems. The traditional pulse width modulated (PWM) Inverter does not completely eliminate the unwanted harmonics in the output waveform. Using the multilevel inverter as an alternative to traditional PWM inverters for electric motor drive applications is investigated. The concept of the Optimized Harmonic Elimination Stepped-Waveform (OHESW) technique for a multilevel inverter is presented. The effectiveness of this technique in minimizing the inverter switching losses and its output voltage harmonic content which cause reducing harmonic losses and torque pulsations of an induction motor fed form is investigated analytically. Comparison between the Selective Harmonic Eliminated PWM (SHEPWM) as a traditional PWM technique for three-level inverter and the OHESW technique for multilevel inverter with regard to the switching losses, harmonic distortion, additional harmonic losses in the motor and the pulsating torques is also presented.

Non-Intrusive Efficiency Estimation of Inverter-Fed Induction Motors

The use of inverter supplies over sinusoidal supplies for induction motors is growing considerably. Inverter supplies enable effective and robust control of induction motors in many automated systems. However, this benefit features at the expense of additional harmonic motor losses due to pulse-width modulated (PWM) voltages and currents produced by inverter supplies. The quantification of these additional harmonic losses and the estimation of efficiency in a non-intrusive manner can be quite challenging. This paper proposes a non-intrusive efficiency estimation technique for inverter–fed induction motors that is based on harmonic regression analysis, harmonic equivalent circuit parameter estimation and harmonic loss analysis using limited measured data. The efficiency results from the proposed technique are comparable to those obtained using the IEC 60034-2-3 Standard up to 1% accuracy when tested on three different inverter-fed motors at different loads.

Analysis of the Influence of Harmonics on Energy Efficiency of Typical Equipment in Distribution Network

With the continuous development of power systems, the number of non-linear loads is increasing. When harmonics flow through wires, transformers, filters, and other devices, additional harmonic losses will be generated, which will cause power loss and safety problems such as equipment overheating. However, there are few studies on loss in complex power quality environments. Considering the influence of skin effect when harmonics flow through the conductor, this paper studies the distribution of current density, explores the influence of conductor material, radius, and frequency of the current flowing through the metal on the current distribution, and proposes a calculation method of conductor harmonic resistance considering the influence of skin effect. Furthermore, the electrical energy consumption of typical devices in the distribution network is considered. Based on the theoretical calculation model, a simulation platform was established to carry out the equipment loss measurement experiment under each harmonic current, and the mutual verification between the theoretical calculation model and the experimental measurement was realized.

Harmonic Loss Analysis of Low-Voltage Distribution Network Integrated with Distributed Photovoltaic

In a power system with highly proportional renewable energy integration, the power generated by photovoltaic (PV) of high permeability and high proportion needs to be connected to the distribution network through the power electronic inverter. The inverters can generate the low-order harmonic and high-order harmonic near the switching frequency. Harmonic power will be generated when the harmonic current flows through the power grid with the harmonic voltage of the same frequency, and the additional harmonic losses caused should not be neglected. To effectively analyze the voltage quality and calculate the harmonic loss of the low-voltage distribution network integrated with distributed PV, based on the harmonic loss factor of resistance proposed, the harmonic impedance modeling and harmonic loss calculation method for the key equipment of the power grid, such as lines and transformers, are introduced in this paper firstly. Next, a decoupling algorithm of harmonic power flow is proposed, and the influence of the access capacity of PV on voltage quality and line loss of the distribution network is analyzed. Finally, a harmonic loss calculation method based on measured harmonic data of the distribution network is proposed. It is found that the harmonic loss of the low-voltage distribution network accounts for about 0.6% of the total network loss. Therefore, voltage quality can be improved and line loss can be reduced effectively by reasonable access to PV and reducing harmonic order and the current harmonic distortion.

Calculation of harmonic losses and ampacity in low-voltage power cables when used for feeding large LED lighting loads

A numerical investigation on the harmonic disturbances in low-voltage cables feeding large LED loads is reported. A frequency domain analysis on several commercially-available LEDs was performed to investigate the signature of the harmonic current injected into the power system. Four-core cables and four single-core cable arrangements (three phases and neutral) of small, medium, and large conductor cross sections, with the neutral conductor cross section approximately equal to the half of the phase conductors, were examined. The cables were modelled by using electromagnetic finite-element analysis software. High harmonic power losses (up to 2.5 times the value corresponding to an undistorted current of the same rms value of the first harmonic of the LED current) were found. A generalized ampacity model was employed for re-rating the cables. It was found that the cross section of the neutral conductor plays an important role in the derating of the cable ampacity due to the presence of a high-level of triplen harmonics in the distorted current. The ampacity of the cables should be derated by about 40 %, almost independent of the conductor cross sections. The calculation have shown that an incoming widespread use of LED lamps in lighting could create significant additional harmonic losses in the supplying low-voltage lines, and thus more severely harmonic emission limits should be defined for LED lamps.

Investigation of Additional Harmonic Losses in Induction Motors Driven by PWM Inverters: Variation with Slot Shapes and Load Conditions

Investigation of Additional Harmonic Losses in Induction Motors Driven by PWM Inverters: Variation with Slot Shapes and Load Conditions

Three-Phase Asymmetric Transformer Aging Considering Voltage-Current Harmonic Interactions, Unbalanced Nonlinear Loading, Magnetic Couplings, and Hysteresis

A new aging calculation method for three-phase three-leg power transformers under (un)balanced and (non)sinusoidal operating conditions is proposed where the impacts of magnetic saturation, couplings, and hysteresis are accurately included. The aging estimation is carried out through a recently developed and validated time-domain model of a nonlinear three-phase three-leg transformer. The model outputs are used to compute aging based on Arrhenius' thermal reaction theory. The combined aging effects from transformer core asymmetry and load nonlinearity, as well as current and voltage harmonic interactions from nonsinusoidal input excitations and nonlinear loading are considered in the calculation. The model improves upon the conventional weighted harmonic factor (WHF) approach of aging estimation by direct evaluation of additional fundamental and harmonic losses generated by the iron-core, nonlinear loads, and terminal voltage distortions. The main contribution is a new transformer aging estimation method with wider applicability to three-phase transformers considering harmonic current-voltage interactions from unbalanced nonlinear loads, terminal voltage distortions and imbalances, as well as magnetic hysteresis and flux-coupling effects in asymmetric iron-core structures. Several case studies are presented for comparing the proposed model based aging method with the conventional WHF approach.