Frequently Asked Questions
Oztek - Frequently Asked Questions
Inverter Control Boards
What is the difference between the OZDSP3000 and OZGTI3000?
The OZDSP3000 is an inverter control board that is intended for customers who wish to write their own
application software. Oztek also provides the OZDSP3000 pre-configured with software for a variety of power control applications
including Grid Tie Inverters and Active Front Ends (OZGTI3000), Voltage Mode Inverters (OZVMI3000), and Boost Converters (OZBST3000).
What kind of development tools do I need to create application software for
Oztek Control Boards?
All of our control boards use Texas Instruments Digital Signal Controllers. At a minimum,
you will need the Code Composer Integrated Development Environment (IDE) to be able to compile, link, and create an executable image.
In order to debug your program, you will also need a JTAG Emulator. There are several manufacturers who make USB JTAG emulators that
are compatible with TI digital signal controllers. These manufacturers include Spectrum Digital, Signum Systems, and Black Hawk.
CAN Bootloader Software
What specific hardware configuration does the TMS320F28335 bootloader s/w require?
1) The DSP needs to be able to boot in “Boot From SPI” mode. Oztek control boards have a provision to force the DSP to boot from SPI (a hardware jumper option to pull GPIO85/XA13 in the proper direction at power-up to force the DSP to boot from SPI).
2) In “Boot From SPI” mode, the DSP will boot from the SPI-A interface on the DSP (GPIO16 through GPIO19). The bootloader requires a 128kbit serial EEPROM (25LC128) or larger to be wired to the SPI-A port on the DSP.
3) The bootloader uses the DSP’s CAN-B peripheral on GPIO20/GPIO21 to interface to the CAN bus.
4) The bootloader code derives the SPI EEPROM and CAN serial bit timing assuming the DSP is driven with a 30MHz external clock source.
SCR1xxx Controllers
Why can't I communicate with the Modbus port?
1) Is the SCR board powered? When power is applied to the board the green “SYS OK” LED located around the middle of the board should be blinking.
2) Is the RS-485 cable connected to J20 on the controller?
3) If the SCR board is at the end of the RS-485 line, is termination enabled (jumper installed between pins 2 & 3 at J11)?
4) If using the ULINX RS-485/USB adapter from B&B electronics, are the data and ground lines connected properly and terminator attached (if at the end of the RS-485 line). See
Oztek drawing 10947
for reference.
5) Are the Port, Baud Rate, and Device ID configured properly in the SCC Tool? The port number will depend on the computer being used and where the RS-485 adapter is connected on that computer. This can be determined using the Hardware Device Manager (under System Properties) on your computer. The default baud rate for all SCR controllers is 19200 kbps and the default Device ID is 2.
6) Have you selected the “Connect Communications” option in the SCC Tool? See User’s Manual UM-0041 for more details.
Grid Tie Inverters and Active Front Ends
What DC Link voltage do I need to interface to a 480V line?
Generally, our application code uses center-aligned, space vector pulse width modulation (SVM) techniques for maximum DC Link voltage utilization. Using SVM, the switch-mode AC voltage output of the inverter, before the filter components, is limited by the dead-time of the power stage and any minimum pulse requirements of the IGBT drivers. For example, 3usec of dead-time when switching at 10kHz, results in a maximum achievable duty-cyle of 97%. Depending on the switching frequency, these hardware limitations will set the maximum, peak, line to line output voltage to ~95% to 97% of the DC Link. Note however, that this is the point at which the duty-cycle is clamped, and the controls become non-linear. In practice, you will want to allow several percent duty-cycle for control headroom in order to provide the controller linear operating range. As such, 92-94% is a more practical design value.
The previous discussion addresses the maximum obtainable voltage at the output of the IGBTs. Considering a GTI or AFE converter can source current into the grid, one also has to allow for voltage drops across the filter components at maximum output current. Let's consider a typical 100kW Grid Tie Inverter interfacing to a 480V AC line. At 10% high line, the maximum peak line voltage is 480*1.1*SQRT(2) = 747Vpk. Assumming 30Vpk is dropped across the filter components, the required minimum DC Link voltage is given by (747+30)/0.92 = 845V.