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This paper discusses the modulation methods for ground current suppression. It focuses on the ground current of the grid-connected three-phase transformerless photovoltaic (PV) inverter with unbalanced output filter inductors. The staggered SPWM modulation using three triangular signals displaced by 120 degrees is mentioned for comparison. Aiming at the case of unbalanced output filter inductors,...
The performance of the Grid Connected Inverters (GCIs) (like windmill and large central PV converters) is extremely important related to stable and safety operation of a "Smart Grid" SG. These inverters' control features not only cover the renewable energy conversion and active power feeding into the utility grid but furthermore they cover the helping of the grid voltage stabilization, supporting...
This paper presents a new active anti-islanding detection method for distributed power generation systems. This method is based on introducing a disturbance at the inverter output and observing the behaviour of the voltage at the point of common coupling (PCC), which depends on the impedance connected to the PCC in an islanding situation.
Vector (dq) control is a powerful technique used in high dynamic performance inverters. The transformation of ac into dc quantities allows the controller to be designed as for dc-dc converters, with infinite gain at the steady-state operating point for zero steady-state error. It can be easily implemented for three-phase inverters but presents some challenges for single-phase ones. The orthogonal...
This paper deals with the application of a sliding and a PI sliding mode strategy to control a three-phase shunt hybrid power filter (SHPF). The SHPF consists of three-leg voltage source inverter (VSI) bridge. The SHPF ensures full compensation of harmonic phase currents and regulates its self sustaining dc bus voltage. The reference currents are obtained from the nonlinear load currents. The control...
Assuming that STATCOM has no active power losses, the current and voltage analytical expressions of the three-level and dual three-point STATCOMs under the fundamental frequency modulation (FFM) control are presented by means of the theoretical analysis method. Meanwhile, the current and voltage waveforms of two STATCOMs are simulated with the help of Matlab/Simulink. The good agreement between theoretical...
A novel method which can improve medium frequency inverter power supply output waveforms using Delta inverter compensate technology is put forward in this paper. Taking parallel compensation as an example, the theoretical analysis of Delta inverter's compensation principle is given. The novel method can improve inverter output waveform distortion which is caused by voltage source inverter's inherent...
In recent years, voltage and current harmonic problems by the remarkable development of static power converters with nonlinear characteristics have been one of the significant subjects. The authors propose the three phase power quality compensator with five leg circuit by indirect power conversion method. This system can compensate the line voltage harmonics by the series inverter and the load current...
A control method for small domestic power plants using renewable energy is described in this paper. This method is not only capable of optimizing the working point of the plant but also implements active power factor correction and lowers the extant harmonic distortion in the line. The novel element in the proposed complex controller structure is the upper harmonic controller that minimizes the amplitudes...
Three-phase currents of STATCOM with conventional control strategy will be unbalanced and distorted when the STATCOM operates at the condition of non-ideal grid voltages. Special attention was paid to the influence of grid voltage quality on STATCOM current and a new control strategy was presented to counteract the influence in this paper. The unbalance and non-sine distortion of grid voltage causes...
In this study, unified power quality conditioner (UPQC) is designed and simulated by synchronous reference frame theory. The proposed system is comprised of series and shunt inverters which can compensate the sag, swell and unbalance voltage, harmonics and also the reactive power. PI controller is used to stabilize DC link voltage and balance the active power between the shunt and series inverters...
Based on the mathematical model of the current source inverter (CSI) in the stationary alphabeta frame, this paper proposes advanced stationary frame voltage control methods for CSI with linear and nonlinear loads to achieve zero steady-state error respectively. The voltage control strategy based on a special resonant controller for CSI with linear loads is firstly analyzed in detail, on the basis...
The operation of photovoltaic (PV) units connected to the system is characterized by several uncertainties due to the number of running units, the points where these units are sited, the exported power and the injection of harmonic currents. The objective of this paper is to investigate the penetration level of PV units in the low voltage (LV) network. Starting from field measurements a model has...
At present, there are two kinds of the high voltage and large capacity inverter, namely multilevel and multi-pulse inverters. In this paper, multi-pulse inverters are classified into two types according to the interphase transformer configuration. At first, the fundamental and harmonic voltage amplitude expressions of two types of the multi-pulse inverter are proposed and used to analyze the relationship...
Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first used in driving electrical motors with variable speed but now due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices...
Unstable problem of PMSM current control system in the overmodulation range of an inverter is a well known problem, however, the cause and mechanism of this problem are still not investigated well. Actually, the main reasons which are large amount of harmonic components and voltage saturation of an inverter in this range are already known. However, the effects from current controller such as PI controller...
Fuel cell power systems have increasingly become popular because of their inherent advantages over conventional energy systems. A fuel cell system typically requires some kind of power conditioning that usually includes a DC-DC converter and a DC-AC inverter. In a single phase system, the operation of a single phase inverter introduces a second harmonic (120 Hz) current ripple into the system. This...
In this paper, a novel topology for single-phase 7-Level inverter is introduced. Structural parts of the inverter are described in detail. Switching strategyand operational principles of the proposed inverter are explained and operational topologies are respectively given. A method and a formula are improved for calculating switching angles. The validity of the proposed inverter is verified through...
The feasibility of neural networks for optimal voltage control of three-phase power inverters was investigated. The case study involved elimination of the 5th, 7th, and 11th harmonics of the output voltage using four switching angles per quarter-cycle of the output frequency. Regular and sparse neural networks were experimented with. The regular network requires training, but the number of neurons...
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