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In this paper, an improved grid voltage modulated control (GVM) with power compensation is proposed for grid-connected voltage inverters when the grid voltage is unbalanced. The objective of the proposed control is to remove the power ripple and to improve current quality. Three power compensation objectives are selected to eliminate the negative sequence components of currents. The modified GVM method...
This paper presents an analytical method developed to explain the mechanism of harmonic transfer between the ac and dc sides of a single-phase inverter in a PV microgrid. The model explains how the feed-forward of the current from the ac side of the PV-inverter into the control system, causes even harmonics on the dc voltage. It further shows how the controller's feedback of the dc bus voltage carrying...
Low-frequency switching strategies are considered as an effective way of achieving efficient performance in multilevel inverters. Selective harmonic elimination (SHE) is a modulation technique of this category which gives a superior outcome suppressing low-order detrimental harmonics. Limited number of decision variables offered by SHE in the corresponding nonlinear equations hinders obtaining quality...
Selective Harmonic Elimination (SHE) is an established technique to eliminate unwanted harmonics that causes aliasing effect in communication systems and affects power quality in electrical systems. In this paper, an analytical approach for SHE is proposed for harmonic elimination in a multilevel inverter. Traditionally, numerical methods like Newton Raphson Algorithm are opted to solve the transcendental...
This paper presents high-power-density inverter with pulse current injection power decoupling method. In order to reduce the dc-link capacitor significantly, dc-link current is fully analyzed with double Fourier method in theory. Compared with the traditional 2nd harmonic power decoupling method, the pulse current injection method considers not only 2nd order harmonic but also the higher order harmonics...
Selective harmonic elimination technique can eliminate any order harmonics theoretically, but it is restricted by the initial value of switching angles and the switching speed of power device, therefore, it has surplus high-order harmonics. The surplus harmonics exist in the form of harmonics group, there is a window which harmonic wave amplitude close to zero between the adjacent harmonic group....
This paper investigates about the impact of the number of levels and of the corresponding modulations angles on the mitigation of harmonics in cascaded H-bridge multilevel inverters. A mathematical model to reduce Nth odd harmonics from the output voltage of a multilevel converter is represented as a constrained optimization problem. It is further transformed in an unconstrained optimization problem...
The well known Selective Harmonic Elimination pulse width modulation (SHE-PWM) is widely used by medium voltage drive applications due its symmetry and control of the low order harmonics that affect output torque, even with low switching frequency. However, the complete harmonic elimination limits the maximum output voltage available, a critical problem for applications where the dc bus voltage level...
This paper presents a generic output model of multilevel inverters formed through cascaded H-bridges and their flexibility in attaining desired harmonic levels, which could also include elimination of the selected harmonics. The signal model of the possible outputs of a multilevel inverter is mathematically represented and then compared with a conventional signal model that is based on harmonic decomposition...
Generally, selective harmonic elimination (SHE) complexity for multilevel converters increases with the increase in number of levels. In this paper, an approach for multilevel converters' SHE is introduced. This approach is based on cancelling the 5th and 7th order harmonics irrelevant of the number of levels in three-phase cascaded-type multilevel converters with unequal DC sources, such that the...
A novel and simple control technique for reducing current harmonics in a grid connected non linear load using composite observer is discussed in this paper. In this scheme, In-phase and Quadrature components of fundamental as well as harmonics of load current and inverter current are estimated using composite observer. Estimated harmonics from the load current are fed forward to generate the control...
This paper presents a 11 level cascade multilevel inverter which implements the popularly used MPPT algorithms Perturb and Observe and Incremental Conductance on the PV array which powers the multilevel inverter. Adaptive Neuro Fuzzy Inference System (ANFIS) based controller switching scheme is used to improve the power quality thus to reduce the Total Harmonic Distortion (THD). The performances are...
The major concern in the design of inverters is dealing with harmonics. Harmonics in inverter are generated due to improper selection of switching angles to the gates of the inverter switches. The presence of harmonics in inverter output will affect the loads connected to it. This paper deals with the selective harmonic elimination problem in multilevel inverter using Artificial Neural Networks (ANN)...
The purpose of this paper is to provide low cost, high power quality and high efficiency solutions for grid-connected inverters. Compared with bipolar switched inverters, unipolar switched inverters have the advantages of higher efficiency due to reduced switching frequency and low iron losses of inductor in output filter. However, unipolar inverters produce large harmonic distortion due to the dead-time...
One of the major problems in electric power quality is the harmonic contents. This paper focuses on elimination (reduction) of harmonics in a H-bridge multi-level voltage-source inverter. Here the basic concept is to eliminate specific harmonics with a proper choice of switching angles. This technique is very efficient for improving the multi-level inverter output voltage quality. In This paper, Generalized...
This paper presents simulation results by using Matlab/Simulink for the assessment of harmonic and interharmonic currents generated by the voltage source inverter (VSI)-fed adjustable speed drives (ASDs). In the simulation, the commutation effects caused by source impedance and non-ideal supply voltages are included. The front-end converter, dc link, pulse-width modulated (PWM) inverter, and the induction...
Multilevel inverters introduce harmonic to the network, beside their enormous advantages. THD is one of the most important indexes to evaluate harmonic contents of waveforms. Conventional method of line voltage THD calculation gives approximate answers but its accurate value is important. In this paper, a series of analytical formula is found to calculate line voltage THD of 5-level inverter with...
Inverters are power devices used for many industrial applications such as power conversion, the speed control of induction motors etc. When a magnetic device is energized by an inverter power supply, its magnetic core is subjected to additional core losses due to harmonic contents. One solution to this problem may be the selective harmonic elimination based on the simultaneous solution of non-linear...
Capacitor Commutated Converter (CCC) is a new kind of converter characterized by having capacitors inserted in between the converter transformer and the converter valves. Its behavior as harmonic source is the research point of this paper. Characteristic harmonics at the dc and ac side of CCC-HVDC system are studied, analyzed and compared with the Line Commutated Converter HVDC (LCC-HVDC) system....
Recently multilevel inverter technology has been a very important alternative in the applications which requires multiple separated DC voltage sources such as solar and fuel cells. But as the number of levels and switching devices which must be used increase circuit becomes more open to faults. Furthermore the complexity of both the circuit and the control method rises. In this paper an improved cascaded...
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