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The Analysis of Output filter for Grid Connected Single Phase Full Bridge Inverter Based on PSpice Simulation Technique P. Khamphakdi and W. Khan-ngern Faculty of Engineering and Research Center for Communications and Information Technology King Mongkut's Institute of Technology Ladkrabang (KMITL ), Bangkok, 10520 Thailand. Phone/Fax: +662 737-3000 Ext.3322, E-mail: [email protected] , [email protected] Abstract This paper presents the analysis of output filter for grid connected single phase full bridge inverter which is SPWM bipolar switching type. Voltage and current output harmonics are analyzed and corrected by low pass filter circuits. LC filter are designed and simulated on PSpice 9.1(student version) simulation technique based on the grid connection regulation in power quality issue. Keywords: Grid connected, inverter, PSpice, filter design 1. Introduction Several governments and utilities worldwide promote the renewable energy such as Photovoltaic (PV), Fuel cell, micro turbines and other conversion technologies for distributed power (DP) generator. In Thailand, the PV station is built on many places of remote area residential, communal building. With the increased utilization of DP connected to the home, these power quality problems are expected to increase [1]. Distortion of sinusoidal voltage and current wave form caused by harmonics from grid connected inverter is one of the major power quality. The passive filters are the most conventional for attenuated the harmonics from the power grid connected inverter because it is easy to use without any addition control part. However, the filter design is quite difficult for calculation and material supports. This paper introduces the low pass filter design for the inverter by calculation and simulation with PSpice student version. This method benefits to reduce the design period. 2. Theory 2.1 Grid connected Inverter Topology Distributed power and in particular PV inverters are currently based on single-phase self– commutated voltage - source inverters for individual households. This inverter consists of different power stages, with high – frequency and line- frequency transformers or even tranformerless design [2]. For increasing efficiency reasons, transformers less topologies have been proposed; isolation transformer is required for safety requirement. To comply with the IEC 61000-3-2 standard [3], these inverters use pulse - width modulation (PWM) controllers to generate sinusoidal output currents. In practice, switching frequency 20-500 kHz is used in different power stages with mainly metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) as switching elements for these PV inverter. This paper use single-stage pulse- width modulated (PWM) dc to ac converter topology (H- Bridge), directly coupled to the grid via a low- frequency isolation transformer and filters shown in Fig.1. filter Lg Vgrid Vdc Fig. 1 Grid connected inverter topology 2.2 Inverter controllers and Harmonics [4] The sinusoidal PWM (SPWM) bipolar switching type is the most popular controller for the inverter. Before discussing the harmonics from inverter, it is necessary to define a few terms. The triangular waveform ( tri v ) in Fig 2. is switching frequency s f , which establishes the frequency that the inverter switches are switched. ( s f is also called the carrier or switching frequency). The control signal con v is used to modulate the switch duty ratio with frequency 1 f , which is the desired fundamental frequency of the inverter voltage output ( 1 f is also called the modulating frequency), recognizing that the inverter output will not be a perfect sine wave and will contain voltage components at harmonic frequencies of 1 f . The amplitude modulation ratio a m is defined as: control a tri V m V ∧ ∧ = (1)
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