APPLICATION OF MODEL BASED SYSTEM ENGINEERING APPROACH INTHE MODELLING OF INDEPENDENT POWER PRODUCER PHOTOVOLTAIC SYSTEMS D. Luta, W. Fritz, A.K. Raji Cape Peninsula University of Technology, Bellville, Western Cape, South Africa ABSTRACT Model Based System Engineering refers to a formalised practise of systems development through the application of modelling principles, methods, languages and tools to the entire lifecycle of a system. This paper presents the modelling of Independent Power Producer (IPP) photovoltaic systems using SysML (System Modelling Language) which is a modelling language that supports Model Based Systems Engineering (MBSE) practices. Broadly speaking, the modelling of a power system is performed using software such as Matlab, DigSilent, and PowerWorld. These software types allow modelling of a system considering only a specific point of view depending on the objective that is to be assessed. SysML offers the advantages of modelling a system considering different aspects such as specifications and requirements, structure and behaviours. This study focuses more specifically on the structure and behaviour of Independent Power Producer. Keywords: Model Based System Engineering (MBSE), System Modelling Language (SysML), Renewable Energy, Photovoltaic Systems, Independent Power Producer (IPP) 1. INTRODUCTION In order to address some of the problems that the world is facing such as environmental destruction, climate change, the increasing world electricity demand and the exhaustion of some of the primary energy sources used for the electrical energy generation, many countries around the world are now focusing their attention on others naturals energy sources. These sources known as renewable energy sources offer the opportunity to cover the world energy demand sustainably without a negative influence on health and nature. As time advances, the electricity generated using renewable energy sources is becoming more significant and seems to be nowadays the type of electrical energy generation going in parity with sustainable growth. Among these renewable energy sources solar power is one of the most promising technologies. Krauter [1] reports that according to the European Commission Energy by 2050, the world could get a fourth of its electricity from solar power.f its electricity from solar power. In Africa in general and South Africa in particular, the level of renewable energy potential especially in term of solar energy is high, for instance most areas in South Africa present an average more than 2 500 hours of sunshine per year, and average solar-radiation levels ranging between 4.5 and 6.5kWh/m2 in one day can be observed [2]. Due to this high level of renewable energy potential, the South African government is making lots of efforts aimed to develop this sector and presently has in place a target of 10 000 GWh of Renewable Energy. The Department of Energy has determined that 3725 MW to be generated from Renewable Energy sources is required to ensure the continued uninterrupted supply of electricity. [3] To reach that target and promote renewable energy sector, the South African Government through the Department of Energy has developed programs. One of them is the Independent Power Producer (IPP) program. The IPP refers to no public electric utility, which owns and or operates facilities to generate electric power for sale to a utility, central government buyer and end users. IPP's may also be privately-held facilities, such as rural solar or wind energy producers, and non-energy industrial concerns generating electric power for on-site use and who may also be capable of feeding excess energy into the distribution or transmission grid system [4]. Once connected to the public electric utility, these IPP’s based mostly on renewable energy sources such as solar or wind bring new challenges and increase the power systems level of complexity due to the unpredictable nature of these renewable energy sources. In order to regulate their operation as grid connected to the public electric utility, these units have to comply with some requirements set by the National Energy Regulator of South Africa (NERSA). In this paper, we present a modelling of the Independent Power Producers (IPP’s) photovoltaic systems based on the Model Based System Engineering (MBSE) approach. Different modelling languages and tools can be used in MBSE, the modelling language adopted in this paper is OMG SysML (Organisation Management Group System Modelling Language). The accent in the modelling will be turned mostly on the structure and the behaviour of these Independent Power Producers (IPP’s) photovoltaic systems. 2. MODEL BASED SYSTEM ENGINEERING Model based System Engineering is an approach of System Engineering defined as a formalised practise of systems development through the application of modelling principles, methods, languages and tools to the entire lifecycle of a system. In Model Based System Engineering, models are taken as the heart of System Engineering activities and also many artefacts [5]. Many years ago, the design of systems was based on System Engineering process workflows using textual documents and engineering data, lots of efforts needed to be made in order to ensure that the information consistency between the system stakeholders is maintained. Such approach called Document Based System Engineering increases risk of inconsistency and incompleteness in the design specification and process which cover such areas as Performance and Reliability. a battery bank both connected to the utility grid though the secondary of an electrical distribution network. designing and verifying complex systems which may include hardware. Figure 3 IPP Photovoltaic configuration . then make engineering tradeoffs. software. and re-simulate until our design meets the specified requirements. and constraints on system blocks that allow us to simulate how a system will behave. Internal block diagrams describe the internals of a block such as parts. CASE STUDY As case study. information. Structure Blocks can be used to represent hardware. Block definition diagrams represent system structure. techniques and tools used in System Engineering. Figure 2 Four pillars of SysML [9] 4. SysML is intended to unify all these languages. Figure 1 SysML and UML Relationship [8] SysML extends the characteristics of UML and replaces the classes and objects by modeling blocks of System Engineering. physical laws. The intersection of the two circles indicates the UML diagrams that SysML reuses whereas the rest part of SysML circle (SysML’s extensions to UML) indicates the new modelling diagrams defined for SysML [8]. You can organize Requirements into hierarchies on requirement diagrams. activity diagrams. system specification. system design integration and reuse of system artefacts [6]. and Parametric) are sometimes referred to as Requirement Requirements are generally categorized as Functional Requirements. or just about anything else. and Non-Functional Requirements. The Venn diagram in figure 1 shows the relationship between SysML and UML. Behavior. ports. the architecture of the system as shown in figure 3 includes two individual DC/DC converters for each power source. Besides the IPP photovoltaic and the battery bank mentioned above. SYSTEM MODELLING LANGUAGE (SysML) SysML represents one of the modelling languages used to support Model Based System Engineering approaches. analysing. use cases. Model Based System Engineering aims to facilitate System Engineering activities by improving communications. a triphase inverter and a bi directional meter. there are a wide range of modelling languages. design precision. techniques and tools and serves as a standard modelling language for systems engineering application. According to [7]. personnel. which represent capabilities of a system. sequence diagrams. software. we have considered a system consisting of a small scale Independent Power Producer (IPP) photovoltaic system. Currently. and state machines. and connectors.workflows compromising the verification and validation process workflows. procedures. Our Embedded System Roadmap is built around producing a SysML model that is organized into four sections. 5. Behaviour SysML provides four main constructs to represent different aspects of system behavior. SysML is a general purpose graphical modelling language for specifying. and facilities. Parametric Parametric allow us to define detailed characteristics. Structure. MODELLING METHODOLOGY The modeling methodology adopted in this research is based on the key diagram types of SysML known as the four pillars of SysML (Figure 2). 3. These parts of the overall system model (Requirements. The operation of this IPP photovoltaic system is controlled by a supervisory and control system unit. Four different operating mode have been selected for this study . At present he is a Master student in Electrical Engineering at the Cape Peninsula University of Technology. Co-Author: Dr Wilfred Fritz is a senior lecturer at the Department of Electrical Engineering at CPUT. . At present he is a Senior Lecturer. MTech and DTech (CPUT) degrees. Raji holds a DTech degree in Electrical Engineering from the Cape Peninsula University of Technology. He is a registered Certified Measurement and Verification Professional (CMVP) and also a professional engineer (Pr Eng) affiliated to the Association of Energy Engineers (AEE) and ECSA respectively. Luta holds a BEng degree in Electrical Engineering from the Higher Institute of Applied Techniques (ISTA) in the DR Congo. Co Author: Dr Atanda K. BTech coordinator and Power Electronics stream leader at the Cape Peninsula University of Technology.Principal Author: Doudou. N. holds BEng (Stellenbosch University).