Download Project Proposal - ECE Senior Design

2013 International Future Energy Challenge Proposal
High efficient grid-tied microinverter
for photovoltaic panels
Team 163
Team members: Muhammad Mustaqeem Khatri
Alfredo Elias
Joshua Ivaldi
Kevin McDowall
Advisor: Dr. Sung Yeul Park
Mentor: Yong-Duk Lee
University of Connecticut
Department of Electrical and Computer Engineering
Summary
We will be designing a microinverter for a solar photovoltaic panel that will take about
18-40 DC voltage from the panel, convert it to 240V AC and then connect it with the grid. If the
connection to the grid is removed, the microinverter will operate in a standalone condition and
provide power to the building that it is installed at.
Background
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 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 a single PV panel power system, a microinverter is used.
In order to integrate or operate a 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. In order to protect other devices on the grid, the microinverter needs 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.
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 will be significantly beneficiary in
the residential applications to maintain critical loads during the power outage due to either heavy
storm or sever hurricane. Filter design and mode transition will be considered additionally for
grid-connection mode and standalone mode.
Solutions
We will use a two power stage system: one is a grid connected inverter for output grid
connection, and the other is a boost converter for PV low voltage input. A digital signal
processor (DSP) provides all pulse width modulation (PWM) signals to the power stage with
respect to the feedback signals based on the voltages and current sensors.
To accommodate a large input voltage range, a two stage topology is generally used, as
shown in Fig.1. The first stages of the flyback converter boost the low voltage of the PV panel to
high voltage DC with isolation. The topology used in the first stage can be simple boost. The
second stage of the inverter produces sinusoidal output voltage and current in synchronization
with the grid voltage. The general topology used for this stage is full bridge configuration.
The grid connected inverter stage is designed with a full bridge inverter, LCL filter, EMI/EMC
filter and static transfer switch (SST). The grid connected inverter is used to achieve sinusoidal
output voltage and current that is in phase and in synch with the grid. The boosted dc-link
voltage by flyback converter is converted to sinusoidal output current and voltage in phase with
the grid. An EMI/EMC filter is used to suppress the EMI/EMC noise and provide impedance
between inverter output and the grid. The auxiliary power for the controller and all feedback
circuitry is derived from the PV panel voltage.
For the convenient programming and design, a high performance, low cost digital signal
controller will be necessary. A wide bandwidth processor is required for this application to better
control voltage and current loops. It will also provide better noise immunity with less
susceptibility to environmental changes. Finally, we will use the TI TMS320F28035 processor,
which provides proper number of high resolution PWM outputs, 12-bit analog to digital
converter inputs, and man-machine-interface required in this application.
DSP will utilize A/D ports for input voltage, input current, dc voltage, output voltage,
output current, and three additional auxiliary analog/ digital ports. This processor also provides
peripheral circuits such as RS-232 and CAN as shown in Fig. 1. In addition, control algorithms
with TI TMS320F28335 processor include controlling power flow from the PV panel to the grid,
the MPPT algorithm, fault control, and optional digital communication routines.
The DSP will have control algorithms for all parts of the design. For the DC-AC inverter
grid connected and standalone modes, there will be algorithms for digital phase lock loop,
current/voltage control, anti-islanding, and grid synchronization. Digital phase lock loop
generates the grid voltage’s frequency and phase angle for the control to synchronize the output
to the grid. Islanding is the continued operation of the inverter when the grid has been removed
intentionally, by accident, or by damage. In the event of such an event, the anti-islanding
protection will then stop supplying power to the grid.
The DC-DC boost converter will also require algorithms for voltage boost controls and
maximum power point tracking (MPPT). MPPT is required in order to optimize the power
harvest from solar panels. The voltage control of the boost converter algorithm is needed in
controlling the pulse width modulation (PWM) of the controller. Finally, there will we
algorithms for protection and load balance.
Project timeline
Oct
Research Item
Nov
Dec
3 4 1 2 3 4 1
Jan Feb Mar Apr
Schematics + Part List
PCB Layout
Prototype Design Parts Order
PCB Order
Board Assembly
Hardware
Functions
Board Testing
Algorithm
Power Test
Revision
Budget
Table 1 below shows the items we will need to accomplish this project and their estimated costs.
Item
Flyback converter
Single phase converter
DSP and Development System
Packaging
Components
Cost
$200
$500
$300
$200
$300
We have been provided $1,000 in funding from the University of Connecticut Electrical and
Computer Engineering Department and $500 in funding from the Office of Undergraduate
Research Grant. Both our total cost and funding are estimated to be $1,500.
Team members information
The team will consist of four undergraduate students and one graduate student with
advising Dr. Sung Yeul Park. This competition will be considered a senior design project for four
of the undergraduate students and thus they will be challenged to use their knowledge in this
design
Yong-Duk Lee received the B.S in electronic engineering and M.S degrees in electrical
engineering from Hankyong National University, South Korea, in 2006 and 2008, respectively.
From 2007 to 2010, he had worked for POSCO ICT as an associate researcher, during which he
was involved in a number of power electronics projects including capacitor charging power
supply (CCPS), plasma power supply, battery energy storage system (BESS). Since 2011, he is
working toward his Ph.D. in Power Electronics, at the University of Connecticut.
Muhammad Mustaqeem Khatri is a senior in electrical engineering at UConn. Over the
summer he has worked as an electronic technician debugging motor drives and power supplies
and so has experience in power electronics. Muhammad’s contribution to the project lies in
programming the microcontroller and working on the DSP side of the board
Alfredo Elias is a senior in electrical engineering at UConn. He has a passion for
alternate energy methods. He is enrolled in the Air Force ROTC program and will commission as
a 2nd Lieutenant once he graduates. Alfredo will be programming the microcontroller as well and
will be implementing MPPT algorithm.
Kevin McDowall and Joshua Ivaldi are seniors in electrical engineering at UConn.
They are participating in this project because of their interest in power electronics and control
theory. Kevin and Joshua are to focus on PCB layout and construction of the power stages of the
circuit.