SEC598F16 Photovoltaic Systems Engineering Session 12 PV System Components Inverters Balance of Systems (BOS) October 04, 2016

Session 11 content Inverters Balance of Systems o Purpose, utility o Operation, reliability, failure mechanisms 2

Learning Outcomes Continued introduction to the power electronics used in PV systems Recognition of the importance of inverters to the operation of certain PV systems Understanding of BOS components and their value to PV systems 3

PV Systems – Charge Controllers and Inverters 4 A simplified version of a grid-tied PV system with battery backup

PV Systems - Maximum Power Point Tracking 5 The PV system produces electrical power and is best utilized when the maximum power produced can be fully delivered to the electrical “load” – this can only happen when the power source and the power load “match” C.S.Solanki, Solar Photovoltaic Technology and Systems

PV Systems - MPPT 6 An approach to assuring a better match is the use of Maximum Power Point Tracking (MPPT) – an electronic technique that moves the operating point along the maximum power hyperbola (I*V = constant) associated with the PV array until it intersects the electronic load IV characteristic

PV Systems - MPPT 7  Perturb and Observe PV operating points from P&O algorithm N.Fermia et al., Power Electronics and Control Techniques for Maximum Harvesting in PV Systems

PV Systems - MPPT 8  Perturb and Observe N.Fermia et al., Power Electronics and Control Techniques for Maximum Harvesting in PV Systems Time domain behavior

PV Systems - MPPT 9  Perturb and Observe P&O flowchart

PV Systems - MPPT 10 I MPPT V MPPT V mp I mp

PV Systems - MPPT 11 MPPT I MPPT I mp V mp V MPPT

PV Systems - MPPT 12  Perturb and Observe, and DC/DC conversion N.Fermia et al., Power Electronics and Control Techniques for Maximum Harvesting in PV Systems

PV Systems - Inverters The inverter is the essential electronic system that converts the DC electrical output from the PV array into the AC electrical input for the residence, national electrical grid, and so on 13 INVERTER DC inputAC output

PV Systems - Inverters 14 Heart of the inverter – the “H-bridge”

PV Systems - Inverters 15 The H-bridge in operation

PV Systems - Inverters 16 The output of the inverter is controlled by pulse width modulation (PWM)

PV Systems - Inverters State of the Art Inverters: o High efficiency – 98% or higher o Dual independent MPPT systems o Integrated DC disconnect and combiner inputs o No fans or electrolytic capacitors 17

PV Systems - Inverters 18 J.M.Jacob, Power Electronics: Principles and Applications

PV Systems – Balance of Systems (BOS) Components The Balance of System components are the smaller and less expensive items needed to complete the assembly of a PV system Many of the BOS components must meet certain codes and standards. Some of the codes are building codes, others are environmental in nature, others still are electrical codes. Some are specified by national regulatory bodies, others by local authorities In the United States, the National Electrical Code (NEC) specifies the requirements for many BOS components 19

PV Systems – BOS The Balance of System components are the smaller and less expensive items needed to complete the assembly of a PV system o Disconnects o Surge protectors o Overcurrent protection devices o Ground fault detection and interruption devices o Grounding connections o Wiring o Connectors o Receptacles o Enclosures o Combiner boxes o Array mounts 20

PV Systems – BOS Switches, Circuit Breakers, Fuses, Receptacles o All of these electrical components used in the DC sections of the PV system must be rated for DC electricity. Similarly, all of the components used in the AC sections of the PV system must be rated for AC electricity. o The NEC specifies circuit breaker sizes matched to wire sizes:  #10 THHN wire can carry a maximum current of 40A, but the maximum circuit breaker size allowed for use with this wire is 30A o Different voltages require different receptacles:  12 VDC will not damage a receptacle designed for 120 VAC, but 120 VAC will surely damage a 12 VDC receptacle 21

PV Systems – Wire Acronyms 22

PV Systems – BOS Ground Fault Protection o The NEC requires that metallic frames and other metal parts of PV systems be connected to ground – this is done with grounding connectors. o The current leaves the PV array through the positive conductor and the same amount returns in the negative conductor. One of these is also connected to ground at one point in the system, and is then known as the grounded connector. o If the ungrounded connector were to become connected to ground, then current could also flow in the grounding connectors. o This situation is known as a ground fault, and the NEC specifies that if a ground fault occurs, the PV array must then be disconnected from the inverter and electrical loads 23

PV Systems – Inverters 24 A simplified version of a grid-tied utility- interactive PV system

PV Systems – BOS 25 A more detailed version of the grid-tied utility- interactive PV system