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Proceedings ArticleDOI

Implementation of MLI and THD analysis for grid connected PV system and simulation study of voltage stability with change in grid impedance

19 Mar 2015-pp 1-6
TL;DR: A new control scheme is used to generate the PWM pulses for the five level grid connected inverter to get much lesser Total Harmonic Distortion (THD) and the Voltage stability with change in grid impedance and without grid impedance is presented.
Abstract: The recent development in the Photovoltaic system (PV) is because of the concern over the high demand in electricity and it directly produces electric power from the solar energy without any environmental hazards. The gird connected PV system will lose its stability when grid impedance is more. This paper compares the conventional grid connected single phase three level inverter topology with five level inverter grid connected system with PV array as the voltage source. A new control scheme is used to generate the PWM pulses for the five level grid connected inverter to get much lesser Total Harmonic Distortion(THD). It also presents the Voltage stability with change in grid impedance and without grid impedance.
Citations
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01 Jan 1999
TL;DR: In this article, a 1.5 kW prototype single-phase grid-connected PV system incorporating a multilevel cascaded Inverter is presented, and simulation results show the suitability of a control method using an optimised cyclic switching sequence and a Ramptime Zero Average Current Error control algorithm.
Abstract: As part of a joint research project between CREST A and PowerSearch Ltd a 1.5 kW prototype single-phase grid-connected PV system incorporating a multilevel cascaded Inverter is currently under development. This paper reports on the design of the system and its control. Simulation results show the suitability of a control method using an optimised cyclic switching sequence and a Ramptime Zero Average Current Error control algorithm.
References
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Journal ArticleDOI
TL;DR: In this paper, a new method to determine inverter-grid system stability using only the inverter output impedance and the grid impedance is developed, which can be applied to all current-source systems.
Abstract: Grid-connected inverters are known to become unstable when the grid impedance is high. Existing approaches to analyzing such instability are based on inverter control models that account for the grid impedance and the coupling with other grid-connected inverters. A new method to determine inverter-grid system stability using only the inverter output impedance and the grid impedance is developed in this paper. It will be shown that a grid-connected inverter will remain stable if the ratio between the grid impedance and the inverter output impedance satisfies the Nyquist stability criterion. This new impedance-based stability criterion is a generalization to the existing stability criterion for voltage-source systems, and can be applied to all current-source systems. A single-phase solar inverter is studied to demonstrate the application of the proposed method.

1,766 citations

Journal ArticleDOI
11 Jun 1990
TL;DR: In this article, a generalization of the Pulse Width Modulation (PWM) subharmonic method for controlling single-phase or three-phase multilevel voltage source inverters (VSIs) is considered.
Abstract: A generalization of the PWM (pulse width modulation) subharmonic method for controlling single-phase or three-phase multilevel voltage source inverters (VSIs) is considered. Three multilevel PWM techniques for VSI inverters are presented. An analytical expression of the spectral components of the output waveforms covering all the operating conditions is derived. The analysis is based on an extension of Bennet's method. The improvements in harmonic spectrum are pointed out, and several examples are presented which prove the validity of the multilevel modulation. Improvements in the harmonic contents were achieved due to the increased number of levels. >

1,139 citations

Journal ArticleDOI
TL;DR: In this paper, the authors analyze the stability problems of grid connected inverters used in distributed generation and demonstrate that the use of active damping helps to stabilise the system in respect to many different kinds of resonances.
Abstract: The aim of this paper is to analyze the stability problems of grid connected inverters used in distributed generation. Complex controllers (e.g., multiple rotating dq-frames or resonant-based) are often required to compensate low frequency grid voltage background distortion and an LCL-filter is usually adopted for the high frequency one. The possible wide range of grid impedance values (distributed generation is suited for remote areas with radial distribution plants) challenge the stability and the effectiveness of the LCL-filter-based current controlled system. It has been found out and it will be demonstrated in this paper that the use of active damping helps to stabilise the system in respect to many different kinds of resonances. The use of active damping results in an easy plug-in feature of the generation system in a vast range of grid conditions and in a more flexible operation of the overall system able to manage sudden grid changes. In the paper, a vast measurement campaign made on a single-phase system and on a three-phase system used as scale prototypes for photovoltaic and wind turbines, respectively, validate the analysis.

997 citations

Journal ArticleDOI
TL;DR: In this article, a single-phase five-level PWM inverter is presented to alleviate harmonic components of the output voltage and the load current, and the deadbeat controller is designed and implemented on a prototype.
Abstract: A single-phase five-level PWM inverter is presented to alleviate harmonic components of the output voltage and the load current. Operational principles with switching functions are analyzed. To keep the output voltage sinusoidal and to have the high dynamic performances even in the cases of load variations and the partial magnetization in filter inductor, the deadbeat controller is designed and implemented on a prototype. The validity of the proposed inverter is verified through simulation and experiments. To assess the proposed inverter, it is compared with the conventional single-phase three-level PWM inverter under the conditions of identical supply DC voltage and switching frequency. In addition, it is compared with the five-level cascaded PWM inverter.

334 citations

Journal ArticleDOI
TL;DR: An adaptive duty-cycle modulation algorithm is presented that reduces the switching frequency to a minimum necessary to fulfill the dynamic requirements of the system, and switching losses are strongly reduced.
Abstract: Multilevel inverters have emerged as attractive high-power medium-voltage power-conversion systems. They are mainly controlled with high-frequency pulsewidth-modulation methods. This is not suitable for very high-power application due to significant switching losses. This paper presents an adaptive duty-cycle modulation algorithm that reduces the switching frequency to a minimum necessary to fulfill the dynamic requirements of the system. Switching losses are, therefore, strongly reduced. This is achieved by using the slope of the voltage reference to adapt the modulation period to ensure that only one-step change between two voltage levels. Simulation and experimental results are presented for a nine-level cascaded inverter. Voltage waveforms obtained for variable frequencies and amplitudes show similar switching patterns, with a reduced and near-constant number of commutations per cycle, regardless of the reference frequency and amplitude.

206 citations