Abstract
Grid connected inverters play a crucial role in generating energy to be fed to the grid. A filter is commonly used to suppress the switching frequency harmonics produced by the inverter, this being passive, and either an L- or LCL-filter. The latter is smaller in size compared to the L-filter. But choosing the optimal values of the LCL-filter is challenging due to resonance, which can affect stability. This paper presents a simple inverter controller design with an L-filter. The control topology is simple and applied easily using traditional control theory. Fast Fourier Transform analysis is used to compare different grid connected inverter control topologies. The modelled grid connected inverter with the proposed controller complies with the IEEE-1547 standard, and total harmonic distortion of the output current of the modelled inverter has been just 0.25% with an improved output waveform. Experimental work on a commercial PV inverter is then presented, including the effect of strong and weak grid connection. Inverter effects on the resistive load connected at the point of common coupling are presented. Results show that the voltage and current of resistive load, when the grid is interrupted, are increased, which may cause failure or damage for connecting appliances.
Highlights
Understanding the grid code requirements is very important in grid connected inverter
Due to the nonlinearity of switching power electronics of the grid connected inverter, a trial and error methodology was adopted by Elsaharty and Ashour [29] to obtain the value of the L-filter and the LCL-filter to comply with the standard IEEE-1547
The characteristics of a commercial inverter (SB 1700E) are studied; besides this paper describes the behaviour of SB 1700E inverter
Summary
Understanding the grid code requirements is very important in grid connected inverter. The multiple PV inverter based Micro-Grid system presented a more challenging picture, where the PV inverters interaction will cause complex resonance at various frequencies, so the output current will be distorted even when the control design and filter circuit are accurately designed for a single inverter. The inverter voltage and the load angle can be estimated by using (6) and (7), respectively, under the condition of inverter work at unity power factor [18] This mathematical approach and theory will help to design open loop grid connected inverter. In order to overcome the above limitations, this paper presents a simple method to design an optimal control of a grid connected inverter with an L-filter
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