Online extraction of individual harmonics from repetitive signals using a composite asymptotic observer is presented in this paper. The settling period and the bandwidth of the observer depend on how far the observer poles have been placed from the origin of the s-plane or the z-plane. The errors in the magnitude and phase of the extracted components, due to the deviation of the signal from the central frequency of the observer, are made very small by providing an integrated phase-locking arrangement. Further improvement in the accuracy, particularly in the extracted higher harmonics, is due to the introduction of multirate sampling. © 2007 IEEE.

Panappakkam Arumugam Janakiraman

Electric fields

Oscillators (electronic)

PHASE LOCKED LOOPS

HARMONICS EXTRACTION

NONLINEAR CIRCUIT

Electric power systems

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Extraction of Harmonics Using Composite Observers

IEEE Transactions on Power Delivery

A new two-phase, independent control strategy for three-phase three-wire static inverters to reduce unbalance in output voltage is proposed. The three-phase voltage and current signals are processed by the ideal Clarke transform block to yield two single-phase signals, which contain information regarding unbalance and harmonics which may be present in the three-phase signals. If the two single-phase voltage signals could be controlled so that they become equal in magnitude with a phase shift of 90o (ideal alpha beta signals), then the corresponding terminal three-phase voltage signals would become balanced. Singlephase observers are employed to control the fundamental components in the two identical d-q frames created. Simultaneously, when the harmonics are eliminated in the two single-phase channels, the corresponding three-phase voltage signals would become distortion free. Feed-forward compensation can be carried out using the equivalent series-impedance parameters, estimated on-line using a simple identification algorithm. This procedure is not sensitive to frequency and can take care of the voltage drop in the distribution transformer. The simulation and experimental results for a field programmable gate array (FPGA) controlled 60 V table top inverter fabricated in the laboratory are provided. © The Institution of Engineering and Technology 2013.

IET Power Electronics

Two-channel control of three-phase inverters for distortion reduction

A new self-tuned feed-forward control strategy for low-voltage single-phase inverters to reduce the harmonic distortion in the output voltage is proposed. A discrete composite observer enables separate and independent control of the fundamental and harmonic components of the distorted inverter voltage and load current. The observer also facilitates the application of single-phase dq transformation by providing the fundamental in-phase and quadrature signals. In addition, the extracted voltage and load current harmonics from the observer are used for online identification of the series inductance and the equivalent resistance of the LC filter. While the feed-forward compensation is made self-tuned, the leftover harmonic distortion is reduced by small harmonic feedback. Simulation and experimental realization with Cyclone II field-programmable gate array have been carried out. © 2011 IEEE.

IEEE Transactions on Industrial Electronics

Self-tuned feed-forward compensation for harmonic reduction in single-phase low-voltage inverters

A simple and robust procedure with good transient response is proposed for d-q voltage control in conjunction with harmonics reduction in the output of stand-alone single-phase inverters. The distortion in the load voltage waveform is mainly due to the voltage drop in the filter-inductor caused by the harmonic components of the current. For extracting the in-phase and quadrature signals from harmonic-rich periodic waveforms, a composite observer has been developed, which is faster and more accurate than a simple observer. Separate observers have been provided for the voltage and current signals. Feed forward compensation has been obtained by using the quadrature components derived from the composite current observer. Further, an Inverter could be modeled as a feed back control system with the fundamental component as the desired output and the harmonics as the noise creeping into the output. The well-known control strategy of using a large feed back around the noise signal can be employed to reduce its effect at the output, exhibiting low total harmonic distortion under non-linear loads. The controllers can be easily modeled in the discrete-time domain and the ideas can be directly implemented digitally for single-phase inverters controlled by FPGA or DSP chips. © 2010 IEEE.

Reduction of voltage harmonics in single phase inverters using composite observers

This paper proposes a simple harmonic feedback strategy for reduction of output voltage harmonics and the removal of any voltage unbalance due to unbalanced linear and non-linear loads in three-phase inverters. The fundamental components of the voltage and current are controlled in dq frame. Two-phase observers have been used for estimating the fundamental αβ components of the inverter voltage and the load current, which in turn helps to segregate the harmonics from the signal. The observer based control strategy, reduction of harmonic distortion and load voltage balancing by the simple harmonic feedback approach has been verified by simulation and experiments. © 2010 IEEE.

2010 Joint International Conference on Power Electronics, Drives and Energy Systems, PEDES 2010 and 2010 Power India

Reduction of voltage harmonics in three-phase inverters using discrete observers

This paper presents a single chip FPGA (Altera Cyclone II) controlled single phase inverter, programmed for the reduction of harmonics in the output voltage. Separate composite digital observers have been designed for extracting the fundamental and harmonic components of the voltage and the highly distorted current signals, particularly when the inverter supplies nonlinear loads. These observers have been embedded into the FPGA along with the controllers and I/O interfaces. The multiple observers yield very pure in-phase and quadrature voltage signals for use in the outer loop and similar signals for stabilizing the inner current loop. The Inverter could be modeled as a feed back control system with the fundamental component of the voltage as the desired output while the voltage harmonics take the role of noise creeping into the output. To obtain a very low total harmonic distortion in the voltage waveform, the well-known control strategy of using a very large feed back around the noise signal has been employed. © 2010 K. Selvajyothi and P. A. Janakiraman.

Fulltext

VLSI Design

FPGA-based software implementation of series harmonic compensation for single phase inverters

The method of extracting individual harmonics from repetitive signals using multiple asymptotic observers is analyzed in this paper. For proper operation of such a composite observer, it is sufficient if the fundamental frequency is approximately made known because, the implementation exhibits sufficient pass-bandwidth centered on the assumed fundamental as well as the harmonics. However, the settling period and the bandwidth of the observer depend on how far the observer poles have been placed from the origin of the s-plane or the z-plane. The effect of small deviations from the central fundamental frequency of the observer, on the magnitudes and phase angles of the extracted signals is discussed. These parameters assume significance when the composite observer is used in feed back loops. Simulation and experimental results are incorporated. © 2006 IEEE.

Journal	IEEE Transactions on Power Delivery
ISSN	08858977
Open Access	No