Research on FPGA controlled three phase PV inverter using multi carrier PWM control schemes

Abstract

Research on FPGA controlled three phase Photovoltaic (PV) inverter using Multi-Carrier Pulse Width Modulation (MC-PWM) is presented in this article. In this proposed work, reduced active switching count, transformers, Single DC input (SDC), modular topologies and redundancy are key advantages. The proposed three-phase five level Multilevel Inverter (MLI) with SDC source using three-phase transformer is controlled by MC-PWM schemes. To evaluate the performance of the inverter, a Phase Disposition (PD), Phase Opposite Disposition (POD) and Alternate Phase Opposite Disposition (APOD) have been proposed. The effectiveness of the inverter is analyzed in terms of Total Harmonic Distortion (THD) by varying the Modulation Index(MI). Field Programmable Gate Array (FPGA) can realized for generation gating pulses to the inverter. The results were analyzed through MATLAB/Simulink and validated by FPGA based experimental setup.

Introduction

Among the various Renewable Energy Sources(RES), Solar PV energy is highly preferable for electrical power generation because, a number features are associated with solar PV energy such as lower maintenance, noiseless operation, higher efficiency and less maintenance cost. To promote solar electric power generation, the government provides subsidies and loan with lower interest rates. Hence, all sectors are focusing on solar PV based electric power generation [1]. For conversion of DC-AC power, multilevel inverters (MLIs) are concentrated along with PWM control techniques [2]. MLIs offer an excellent performance compared to the conventional inverter such as reduced switching stress; filter size, THD, and modular structures [3]. The MLIs are basically found into (i) Diode Clamped, (ii) Flying capacitor clamped (iii) H-Bridge inverter [4]. With reference to the number of input DC sources and their magnitudes, MLI can be categorized into symmetrical (equal magnitude) and asymmetrical (unequal magnitude) [5]. Symmetrical structure MLIs are familiar for grid connected PV applications with multiple numbers of sources. Cascaded MLI is designed for PV utility application using multiple DC sources with equal magnitude [6]. Asymmetrical MLIs are also designed for PV applications, but the voltage is a key factor while designing voltage steps [7]. Recently, many authors have reported their findings related to MLIs with SDC source instead of multiple sources for single and three phase applications [8]. A three-phase inverter has been investigated using an SDC input with single-phase transformers for grid-connected applications [9]. Three phase MLIs using 3-phase transformers have been considered by the SDC source [10]. This topology is suitable for grid-connected PV applications. Transformer structured topologies are well suitable for utility applications. But, other hand, usage of the transformer also increased corresponding to the number of levels. Therefore, this will make costly as well as bulky. From the discussion, it is found that all the inverter topologies are highly adaptable for standalone photovoltaic (PV) and grid connected applications. A three-phase topology has been designed with a reduced number of active switching devices, but it requires additional power diodes and DC bus capacitors [11]. Recently, the inverter was designed for PV applications using the isolation transformer with three levels of the three-phase inverter [12]. A three phase 4-wire PV interface grid-connected inverter was investigated. This inverter topology generates a 3-level output voltage and required additional filtering circuits [13]. For controlling an inverter, a different multi-carrier PWM technique has been applied [14]. Scott connection based multilevel inverter is discussed. In this topology, two-four leg inverter topologies have been presented for PV grid connected applications [15].. The authors have been reported that, Cascaded MLI with single DC input using a transformer and can be reduced number of power switches. This inverter can realize using FPGA with multi-carrier pulse width modulation [16]. Recently, three -phase inverter has been introduced for PV applications. In this new topology has been developed with by using 24 switches, nine diodes, multiple DC sources and also discussed different PWM techniques [17]. In this article, the three phaseparallel inverter can be controlled by MC-PWM schemes such as APOD, POD, and PD. The inverter performance can be evaluated in terms of THD. In this paper, a three phase modified PV inverter with reduced number of components has been proposed. Comparative analysis is made among the components, switches and transformer. This type of topology is highly suitable for grid connected applications along with renewable energy applications. In this article, the three phase five level inverter can be controlled by MC-PWM schemes such as APOD,POD, PD, and APOD. The inverter performance can be evaluated in terms of THD. In this proposed work, reduced active switching count, and transformers and SDC input are merited. Furthermore, It has a high degree of modularity and redundancy and suitable for RES applications. At the customer point of view, reliability is a great concern in the PV inverter. From the results, it is observed that simulation and experimental results are closer and validated.