ECE 4901FALL 2012

High efficient grid-tied microinverter

for photovoltaic panels

Muhammad Mustaqeem Khatri (Electrical Engineering)

Kevin McDowall (Electrical Engineering)

Joshua Ivaldi (Electrical Engineering)

Alfredo Elias (Electrical Engineering)

University of Connecticut

Depart of Electrical and Computer Engineering

Statement of Need

Nowadays we are faced with problems like depletion of fossil fuel and environment pollution. To solve such problems, many nations and the world’s leading technology vendors are introducing a utilization of renewable energy sources (RES) and its applications. Such representative renewable resources indicate photovoltaic (PV) and wind power generation. Generally, large scales RESs have cost and space problems. In order to avoid these perspectives, small PV system is the best solution on cost effective and applicability. However, in the PV system, the main drawbacks are the high cost of manufacturing silicon solar panels and the low conversion efficiency. However, small PV system can easily achieve RES system with convenience and compatibility.

Generally, in order to implement single PV panel power system, a microinverter is used. In order to integrate or operate microinverter with a single solar panel, we need to consider two important concerns. One is to harvest solar energy as much as possible by applying maximum power point tracking algorithm, because the characteristic of solar power is a kind of variable power source with respect to the sun light and environmental conditions such as cloud and weather conditions. The other is to send power to the grid with respect to the grid voltage sinusoidal angle.

Preliminary Requirement

The main goal of this project is to develop low-cost power processing systems that support the rooftop photovoltaic (PV) installations to provide non-utility and ultra-clean electricity. This project will also be part of the International Future Energy Challenge (IFEC) 2013. Unlike the commercial microinverter, IFEC 2013 requires that the microinverter need to operate not only in the grid-connected condition but also in the standalone condition. That means the microinverter needs to control both output voltage and output current with respect to the operation modes. To operate microinverter in the standalone mode, it will be significantly beneficiary in the residential applications to maintain critical loads during the power outage due to either heavy storm or severe hurricane. Filter design and mode transition will be considered additionally for grid-connection mode and standalone mode.

Basic Limitation

Currently, the cost of power electronics in PV system is around $0.3/Watt. To achieve the goal of $1.5/watt installed PV systems by 2020, a price point that allows the solar energy competing with conventional electricity in the United States, the cost of the power electronics needs to be reduced to $0.1/Watt. Also, since the microinverter will be sending power to the grid, it needs to protect other devices on the grid. The microinverter will need to meet international standards such as IEEE 1547 standards, EN61000-3-2, and U.S. NEC 690. These standards provide grid connection time, procedure, grounding methods, and so on.

Other DataThe team has access to the high quality facilities shown in Fig. 1

The resources of the lab make it ideal for this project. Some of its current assets including software tools are listed:

- Hardware and Equipment:▪ ABC-150 450V/250A 150kVA bidirectional DC power supply▪ AMX3120 12kW programmable AC power source▪ AVTRON 100kW resistive AC load bank▪ 63802 Chroma 3 Phase 10kW AC/DC programmable load▪ Valence 12kWh Li-Ion Battery▪ SAFT 12kWh Water cooled Ni-CD Battery ▪ 208V and 480V 3 phase two power lines in the laboratory▪ WT1800 Yokogawa power analyzer▪ Real Time Digital Simulator (RTDS) ▪ Digital 4 channel high speed oscilloscope▪ 6 High voltage/high current oscilloscope probes▪ 2 SOLECTRIA Electric Vehicles▪ 1 220W PV panel

- Simulation and Design tools:▪ Altium PCB Design Tool▪ Psim simulation Tool▪ Matlab / Simulink▪ COMSOL ▪ Pspice

Questions

Fig.1. Picture of energy storage test bed in the University of Connecticut

One question that has been raised is that which topology for the inverter circuit will give us the most efficient design. One idea was to use the Flyback topology, but it still remains unclear as to which design is the best.

Additional Information

This project will challenge us in various areas including optimal design for the two stage inverter and making the circuit in a confined area, which will require multi-layer PCB. Also, programming skills will also be used in this project for programming the microcontroller.