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

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

3. 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

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

5. PV Systems – DC-DC converters
Boost converter ON
OFF

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

7. PV Systems – DC-DC converters
Buck converter

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

9. PV Systems – DC-DC converters
Buck-Boost converter

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

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

12. 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

13. PV Systems - MPPT
Other representative electrical loads

14. 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

15. 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

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

17. PV Systems - MPPT
Perturb and Observe
P&O flowchart

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

19. 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

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

21. PV Systems - Inverters
The H-bridge in operation

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

23. 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

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

25. 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

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

27. 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

28. 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

29. 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

30. PV Systems - BOS
Modules and Junction Box

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

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

33. PV Systems - BOS
DC disconnect data sticker

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

35. PV Systems - BOS
Main panel and Point of Utility Connection

36. PV Systems - BOS
Main panel and Point of Utility Connection