2013 International Future Energy Challenge
Topic A: Highly efficient grid-tied microinverter for photovoltaic panel
Progress Report
Team Members:
Muhammad Mustaqeem Khatri, Jonathan Blake, Kevin McDowall, Alfredo Elias, Joshua Ivaldi, Yong-Duk Lee
Advisor:
Prof. Sung-Yeul Park
Department of Electrical and Computer Engineering
University of Connecticut
Submitted on: November 30, 2012
1. Progress and UConn Team
1.1 Current Progress
Our team has decided on the circuit topology and has completed the circuit schematic for both the power and the control board for our microinverter. Currently working on the process of making the PCB layout for both of the boards using Altium and will be ready to order all the parts within a week. In the following weeks, we will spend our time coding the microcontroller, testing the circuit board and making any possible improvements.
1.2 UConn Team
This team is comprised of four senior Electrical Engineering students (Muhammad, Kevin, Joshua, and Alfredo) and one junior Electrical Engineering student (Jonathan). We have one graduate student, Yong-Duk, and a team advisor, Dr. Sung Yeul Park. Muhammad and Jonathan have compiled the part list for the control board and have created the foot prints from them. They are currently working on finishing the PCB layout for the control board. Similarly, Kevin and Joshua have compiled the parts list for the power board and are working on finishing the foot prints and the PCB layout for them. Alfredo is doing similar work for the gate driver portion of the circuit.
1.3 School Support
Our Electrical and Computer Engineering department has provided us with a budget of $1000. We have also received an additional $500 in the form of a research grant from our university. Furthermore, our power electronics lab facilities provide us with different equipment that helps us in testing our microinverter. These include: 150 450V/250A 150kVA bidirectional DC power supply, Real Time Digital Simulator, Digital 4 channel high speed oscilloscope, 220W PV panel, and many other devices.
2. Detail circuit design and progress
Fig. 1 shows our overall design of microinverter. We have chosen a flyback converter topology configuration on the front-end converter, because we need to not only boost voltage level but also isolate from primary side to the secondary side for protection purpose. In addition, around 100~1kW power rating, a flyback converter has higher efficiency compared to the other topologies. A snubber has been added to prevent spikes in voltage from switching, and a current sensor has been added for additional protection of the components. The grid tied inverter as a back-end converter will connect to the grid and transfer power as well. This will then be synced with the grid in order to send power with respect to the grid voltage angle. Filters are then used to get rid of the various noises associated with the system and meet the harmonic suppression.
Fig. 1Proposed microinverter configuration.
Fig.2Proposed microinverter external enclosure.
2.1 Flyback Converter Design
Fig. 3 shows schematic design of flyback converter. Input side contains a current sensor, a voltage sensor, solid state relay and electrolyte capacitors. Flyback converter side contains discrete MOSFET, RC snubber, high frequency transformer and freewheeling diode. In order to do boosting and isolation, high frequency transformer is adopted. Its turn ratio is 1:8.
Description / Symbol / Value / UnitEfficiency / η / Min 95 / %
PV voltage range / VPV / 18~40 / V
PV operating current / Impp / 16 / A
Output voltage / Vdc / 400 / V
Output current / Idc_flyback / 1.6 / A
Turn ratio / 1:8
Table I. Specification of Flyback converter.
Fig.3Flyback converter.
2.2 Single Phase grid-tied inverter
Fig. 4 shows single phase grid-tied inverter. This inverter contains module type MOSFET, LC filter, and EMI filter.
Fig.4Single Phase grid-tied inverter.
Table.II Specification of Single Phase grid-tied inverter.
Description / Symbol / Value / UnitEfficiency / η / Min 95 / %
DC Link voltage / Vdc / 400 / V
Output voltage / Vgrid / 240 / Vrms
Output current / Igrid / 2.1 / Arms
Apparent power / Sinv / 500 / VA
2.3 Control board design
2.3.1 DSP controller
Table III shows a specification of DSP controller. This controller contains ADC sensing part, PWM part, digital input/output part and communication part.
Table.III Specification of DSP controller.
Series / TMS320F28x3x Delfino™, C2000™Core Size / 32-Bit
Speed / 150MHz
Connectivity / CAN, EBI/EMI, I²C, McBSP, SCI, SPI, UART/USART
Peripherals / DMA, POR, PWM, WDT
Number of I /O / 88
Data Converters / A/D 16x12b
2.3.2 Gate driver
In order to control Flyback converter and Single phase grid-tied converter, gate driver is designed with MOSFET driver IC. Fig. 5 shows schematic of gate driver.
Fig. 5 Gate driver circuit.
2.4 PCB design of DSP control board
After basic schematic design, we are connecting wire on the layout PCB board shown in Fig. 6. After going through a final check we will be ordering both the PCB and the parts for assembly. In this progress report, we only display control board design due to the page limit. However, we are working on power stage board in parallel.
Fig. 6 DSP Control board PCB layout
2.5 Simulation of proposed microinverter system and results
Fig.7 shows a flyback converter simulation layout and its results shown in Fig. 8. Dc-link voltage regulated after couple of 100 millisecond with 400V level. Figs 9 and 10 show the back-end converter power stage and its results.
Fig.7 Flyback converter simulation model
Fig.8Simulation results detailing input voltage, input power and DC link voltage for DC-side
Fig. 9 Power side simulation model
Fig. 10Simulation results detailing AC grid side voltage, current and power specifications
In PSIM simulation tools, we can build codings with C compiler shown in Fig. 11. It will not only make us to simulate easily but also save our time for DSP coding.
Fig. 11 DSP simulation input and output diagram
2.6 Timeline
Design plan of UConn team is shown in Table. 4. We have a plan to order two PCB boards before the end of semester and order components together. During winter break, we will start to assemble boards and parts. We are targeting to have test results by middle of January 2013.
Table IV: Design plan timeline
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