Current-Fed Quasi Z-Source Inverter based PV Distributed Generation Controller Abstract -- Recently, the renewable photovoltaic distributed generation (PV-DG) enjoys a rapid growth globally due to the advancement in solar systems and power electronics technologies. However, the intermittent nature of solar radiation and performance of the attached power converters, inevitably poses some challenges to the power grids integrated large-scale solar- farms (SF). These challenges include frequency oscillations, voltage variation and power quality issues. To overcome these problems, this study proposes a Current-Fed quasi Z-source Inverter (CF-qZSI) as an alternative converter for distribution generation controllers to facilitate the integration of a PV energy source into a weak power system. The detailed model of the CF- qZSI-based distribution controller (CqZDC) and its control system are developed. The dynamic performance of the CqZDC device is evaluated to validate different objectives using an actual field data and RTDS simulation platform. Index Terms—Accommodation of renewable energy resources, current source inverter, facilitating of distributed electricity generations, frequency stability, power quality improving, wide band gap devices. I. INTRODUCTION Thanks to the recent advancement in renewable energy technologies on account of scientific community and industry contributions, Photovoltaic Distributed Generation (PV-DG) is now significantly considered in supplying electricity amidst distribution networks. One limitation on attaching more and more PV sources to supply higher percentage of the total power demand, is the power quality issues that adversely affected by the penetration and fluctuation in the PV generated power and the negative impact of the attached power converters [1-2]. Additionally, taking a place of the conventional generators by renewable energy sources, results in reducing the overall power system inertia [3-4]. This inertia is favorable for frequency dynamic enhancement, and it becomes not guaranteed due to the detaching of rotating generators that have high kinetic stored energy. This is a gap power conditioning systems (PCS) can fill in. Table I lists the average inertia constant for different generation turbines. TABLE I. INERTIA CONSTANTS FOR DIFFERENT GENERATION TURBINES [4] System Turbine H (s) Steam 4-9 Gas 3-4 Hydro 2-4 Wind 2-5 Solar PV 0 Based on the aforementioned dynamic considerations on integration of a renewable energy distributed generation, the power system developers must improve the quality of the injected power before authorizing interconnection of PV-DG to distribution feeders. The power quality is an electrical term that describes the ability of the electricity supplies to generate a clean and stable power, and can be measured by different parameters involves voltage, current, frequency and power factor. These parameters must obey to the grid codes and standards that required by the Institute of Electrical and Electronics Engineers (IEEE) to assure desirable power quality. These standards and requirements are as follows: 1) Voltage Flicker requirement: The fluctuating nature of power supplied by a PV-DG system can cause of voltage deviations at the grid interfaced bus. These voltage flickers must follow the limits that stated by IEEE-1453 standard. 2) Voltage and current Harmonic requirements: Most of the PV systems require interface power converters, which are significant sources of current harmonics. IEEE-519 standard obtains the acceptable range of the current and voltage harmonics at the Point of Interconnection (POI) bus. 3) Temporary overvoltage (TOV) requirement: This requirement obeys to IEEE-1547 standard that recommends the TOV limits under normal and unbalanced conditions. 4) Power factor requirement: This requirement obey to the Large Generator Interconnection Agreement (LGIA), which necessitates 0.95 power factor at the (POI) bus, calculated at maximum net power [5]. 5) Online frequency requirement: The sudden disturbances in the supplied or consumed active power causes severe variations in the grid frequency that reduces the power stability, especially for the PV side sub-transmission system. Therefore, the online frequency at the output terminal of the PV-DG must be regulated at nominal value with meeting the frequency dynamic criteria, such as rate of change of frequency (ROCOF) and frequency nadir [4]. In order to meet the aforementioned grid requirements, numerous studies ([6-8]) investigated the impact of the static synchronous compensator (STATCOM) in facilitating the integration of renewable energy sources in order to meet the technical voltage specifications required in grid codes. Including an ESS to STATCOM devices, as in PCS, for the purpose of peak power shaving or power supporting during peak time, is also investigated in [9]. In [10], the utilization of a cascaded multilevel converter based STATCOM, to regulate the voltage at the POI, was validate for integration of a large Faris E. Alfaris Student member, IEEE Electrical and Computer Engineering North Carolina State University Raleigh, United States Fealfari@ncsu.edu . Subhashish Bhattacharya Senior member, IEEE Electrical and Computer Engineering North Carolina State University Raleigh, United States Sbhatta4@ncsu.edu 978-1-4799-7312-5/18/$31.00 ©2018 IEEE 6249