Balance of Systems (BOS) Session 10 PV Systems – Part 6 Inverters Balance of Systems (BOS) September 29, 2015

Session 10 content DC-DC converters Inverters Balance of Systems Concluding remarks Inverters Purpose, utility Operation, reliability, failure mechanisms Balance of Systems

Learning Outcomes Introduction to the power electronics used in PV systems Recognition of the importance of controllers and inverters to the operation of PV systems Understanding of BOS components and their value to PV systems

PV Systems – DC-DC converters Boost converter The transfer characteristic is: en.wikipedia.org/wiki/Boost_converter

PV Systems – DC-DC converters Boost converter ON OFF

PV Systems – DC-DC converters Buck converter The transfer characteristic is: en.wikipedia.org/wiki/Buck_converter

PV Systems – DC-DC converters Buck converter

PV Systems – DC-DC converters Buck-Boost converter The transfer characteristic is: en.wikipedia.org/wiki/Buckboost_converter

PV Systems – DC-DC converters Buck-Boost converter

PV Systems – DC-DC converters Summary Boost Converter Buck Converter Buck-boost Converter

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

PV Systems - Maximum Power Point Tracking 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 Other representative electrical loads

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

PV Systems - MPPT Perturb and Observe P&O flowchart

PV Systems - MPPT Perturb and Observe 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 INVERTER DC input AC output

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

PV Systems - Inverters The H-bridge in operation

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

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

PV Systems - Inverters 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

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

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

PV Systems – BOS Switches, Circuit Breakers, Fuses, Receptacles 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. 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 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

PV Systems – BOS Ground Fault Protection The NEC requires that metallic frames and other metal parts of PV systems be connected to ground – this is done with grounding connectors. 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. If the ungrounded connector were to become connected to ground, then current could also flow in the grounding connectors. 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

PV Systems - BOS Modules and Junction Box

PV Systems - BOS DC input from PV array AC ouput from inverter Inverter and DC disconnect

PV Systems - BOS Inverter data sticker Vin = 600 V Iin = 18 A 250 < VMPPT < 600 PAC = 4000 W Inverter data sticker

PV Systems - BOS DC disconnect data sticker

PV Systems - BOS To PUC From inverter PV meter and AC disconnect

PV Systems - BOS Main panel and Point of Utility Connection

PV Systems - BOS Main panel and Point of Utility Connection