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Single-phase current controlled, voltage source inverters are commonly used to feed unity power factor sinusoidal current into the distribution network from PV sources. A large 50 Hz transformer is often used at the inverter output for galvanic isolation and to prevent dc current injection into the distribution network. This transformer increases cost, size and overall power losses of the system....
Multilevel line commutated inverters for renewable energy systems have gained popularity in recent times, especially in the distributed generation where a number of batteries, fuel cells, solar cell, and micro-turbines can be connected through a MLC to feed the grid. They can synthesize higher output voltage levels and can generate near sinusoidal voltages. This paper presents analysis of a grid connected...
Conventional anti-islanding techniques used in grid-tied photovoltaic (PV) systems pose many disadvantages at high levels of PV deployment. One such issue is the inability of these systems to ride-through grid disturbances. In this paper, the use of a Power Line Carrier Communications (PLCC) Permissive anti-islanding scheme is investigated as a means of safely enabling ride-through operation of grid-tied...
Grid connected inverter offers better controllability and better operation, however, there is a risk for local instabilities due to particular control scheme. As long as the input admittance is positive at particular resonance frequency, the risk of local instability can be suppressed. In this paper, the virtual resistor concept is employed to obtain the positive input admittance. Impact of double-loop...
Static Compensator (STATCOM) has been widely proposed for power quality and network stability improvement. It is easily connected in parallel to the electric network and has many advantages for electrical grids. It can improve network stability; power factor, power transfer rating. It can also avoid disturbances such as voltage sag (dip) and swell which is the main concern of this paper. This paper...
The DC/AC inverters are the key elements in grid-connected PV energy production systems. In this paper, new design optimization techniques focused on transformerless (very high efficiency) PV inverters are proposed. They have been developed based on an analysis of the deficiencies of the current, state-of-the-art PV inverters design technology, which limits the amount of PV energy supplied into the...
This paper presents a new micro-inverter topology that is intended for single-phase grid-connected PV systems. The features of the proposed topology are: (1) eliminating the double-frequency power ripple using small film capacitor; (2) improving the maximum-power-point tracking (MPPT) performance; (3) using long life-time film capacitors, which will improve the reliability of the inverter; and (4)...
In the transformerless photovoltaic (PV) system, the common mode ground leakage current may appear due to the galvanic connection between the PV array and the ground, which causes the safety issues and reduces the efficiency. To solve this problem, a novel inverter topology with switched capacitors is proposed in this paper. By connecting one pole of the PV cell directly to the neutral line of the...
As the output power of the photovoltaic (PV) cell changes with the insolation , PV cell temperature and cell voltage changing. It is necessary to control the operating point to draw the maximum power of the PV cell in order to increase system efficiency. In this paper, two-level single phase PV grid-connected system is designed, which mainly includes PV cell, BOOST circuit, inverter, filter and the...
The removal of a transformer in grid-connected PV systems can reduce size, weight and costs. When no transformer is used, a galvanic connection between the grid and PV panels exists and leakage current appears due to parasitic capacitance. In this paper, the principle of leakage current is analyzed from equivalent resonant circuit and an equation is derived to evaluate the current. It will be shown...
This paper proposes a current control strategy with zero steady-state tracking error for grid-connected boost-inverters. Two boost converters are controlled separately to achieve both output current tracking and balanced output voltages. Based on cascading control and feedback linearization, the inner and outer-loop controllers are derived combining the inversion of boost converter model and the output...
In this paper, a high gain single-stage buck-boost grid-connected system is proposed. The proposed system consists of a high voltage gain - high efficiency - switched inductor buck-boost converter (SIBBC) and a folded cascade H-bridge inverter. The proposed converter switch is derived with a sinusoidal modulation, so that the converter output voltage is a rectified sine wave which requires only a...
This study proposes an islanding detection method for use of grid-connected inverter of distributed renewable generation system. The proposed method is based on two indices: the rate of change of voltage (ROCOV) and the rate of change of frequency (ROCOF). When an inverter is grid-connected, the ROCOV and ROCOF are lower than the threshold values. In contrast, as an islanding occurs, the ROCOV or...
The use of small inverter-interfaced distributed energy resources for reactive power support is discussed. While the primary function of these resources is to deliver active power, they can also be used to provide reactive power, often identified as an ancillary service by a utility. Given the large and increasing number of small grid-connected inverters, the total reactive power that can be collectively...
The modular non-isolated inverter structure enhances the efficiency and redundancy of the PV generation system. Current coupling between the transformerless grid-connected inverter modules for PV power system is researched. The operation modes of the non-isolated inverters with different topologies and modulations are analyzed and the current decoupling conditions are obtained. Inverters which are...
Vehicle to grid (V2G) power transfer has been under research for more than a decade because of the large energy reserve of an electric vehicle battery and the potential of thousands of these connected to the grid. In this study a complete analysis of the front end inverter of a non-isolated bidirectional EV/PHEV charger capable of V2G reactive power compensation is presented.
In this paper, a high frequency (HF)-based three-phase Semicontrolled rectifier-current source inverter system is proposed for grid-connected permanent magnet wind generators. The main advantages of the topology are: high efficiency due to less power losses and reduced number of switching elements, high output power density realization, reduced passive component ratings proportionally to the frequency,...
A part of an electric power system can operate as a standalone system without any connection to the main grid. Such autonomous systems include dedicated power systems for rural areas, moveable military bases and facilities requiring premium power quality. For the proper calculation and control operation of autonomous generation systems, the dynamics of the power sources and the loads must be properly...
This paper presents a software-based adaptive dead-time compensation technique for single-phase grid-connected photovoltaic (PV) inverter system. To prevent a short circuit in the dc-link, a switching delay time is needed to be inserted in Pulse Width Modulation (PWM) signals. This causes the dead-time effect which is harmful to the system performance. To improve the mitigation of dead-time effect...
This paper proposes a cost effective, simple, and effective method to prevent islanding of grid-connected inverters. It discusses the shortcomings of previous passive and active methods to prevent islanding of utility interactive inverters. A new method, in which the inverter interfacing the main grid and a microgrid is periodically operated in the over-modulation region is proposed. Islanding is...
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