INTEGRATION OF SINGLE-STAGE SPV GENERATION USING PI CONTROL WITH ADMITTANCE BASED LMS TECHNIQUE

An integration of single-stage solar photovoltaic (SPV) generation to three-phase AC grid using PI control of admittance based LMS (Least Mean Square) adaptive control approach is proposed in this paper. The proposed control is easy to implement and has a fast response. To mitigate several power quality issues like current harmonics distortion, reactive power and load unbalancing the proposed method is developed. The main focus of the system is to supply active power to the grid as well as loads at PCC. A simple LMS based admittance control with P&O (Perturb and Observe) based MPPT (Maximum Power Point Tracking) is used for achieving efficient system. Here we are using the fuzzy controller compared to other controllers i.e. the fuzzy controller is the most suitable for the human decision-making mechanism, providing the operation of an electronic system with decisions of experts. By using the simulation results the proposed method is analyzed under variable solar irradiance, balanced and unbalanced load (linear and nonlinear) conditions in both PFC and ZVR modes. INTRODUCTION Solar PV has specific advantages as an energy source: its operation generates no pollution and no greenhouse gas emissions once installed, it shows simple scalability in respect of power needs and silicon has large availability in the Earth‟s crust. The various configurations of integration of the solar PV systems are single-stage single phase system, double-stage single phase system, single stage three phase system, double-stage three phase system, single-stage three phase four wire system and double-stage three phase four wire system etc. have been presented. Today grid integration of solar PV (Photovoltaic) systems are emerging technology [1] in the distribution system due to eco friendly, renewable, battery less, supplying active power to grid as well as loads and mitigates the distribution power quality problems like reactive power load balancing, current harmonics distortions etc. Single-stage topology is demonstrated more operative for applications with higher voltage levels and it has less power losses [6]. All these control approaches are used to generate required pulses for VSC in both PFC and ZVR modes. Moreover, in single stage topology different maximum power point tracking International Journal of Scientific Research in Engineering (IJSRE) Vol. 1 (4), April, 2017 IJSRE Vol. 1 (4), April, 2017 www.ijsre. in Page 91 (MPPT) approaches have been reported in [7] to generate reference signal for the VSC control algorithm. Maximum power point tracking (MPPT or sometimes just PPT) is a technique used commonly with wind turbines and photovoltaic (PV) solar systems to maximize power extraction under all conditions. PV solar systems exist in many different configurations with regard to their relationship to inverter systems, external grids, battery banks, or other electrical loads. [5] Regardless of the ultimate destination of the solar power, though, the central problem addressed by MPPT is that the efficiency of power transfer from the solar cell depends on both the amount of sunlight falling on the solar panels and the electrical characteristics of the load. As the amount of sunlight varies, the load characteristic that gives the highest power transfer efficiency changes, so that the efficiency of the system is optimized when the load characteristic changes to keep the power transfer at highest efficiency. This load characteristic is called the maximum power point. In this paper, a single-stage SPV generation is integrated to three-phase distribution grid using a admittance based LMS (Least Mean Square) adaptive control [8] incorporating a perturb and observe (P&O) based MPPT methodology. The proposed control is easy to implement and has very fast response. The performance of the system is simulated in MATLAB environment under variable solar irradiance, balanced and unbalanced loads conditions in both power factor correction (PFC) and zero voltage regulation (ZVR) modes. CONTROL STRATEGY Figure 1 shows the proposed single stage SPV system connected to three phase distribution grid. The parameters of the system are given in Appendix. The control architecture of the proposed system is shown in Fig. 2. This control approach uses a single-stage converter topology to achieve two basic functions: MPPT and switching of the VSC. The details of the MPPT control and admittance based LMS adaptive control is given in the section below. A. MPPT Control When a load is directly connected to the solar panel, the operating point of the panel will rarely be at peak power. The impedance seen by the panel derives the operating point of the solar panel. Thus by varying the impedance seen by the panel, the operating point can be moved towards peak power point. Since panels are DC devices, DC-DC converters must be utilized to transform the impedance of one circuit (source) to the other circuit (load). Out of different MPPT methods reported in the literature [7], the hill climbing or P&O approach is used here due to its generic nature and simplicity. B. Admittance based LMS Adaptive Control Approach 1) Estimation of unit templates From the sensed PCC voltages (vab and vbc), the phase voltages are obtained from equation in [9] as