Frequently Asked Questions
OZPCS-RS40
Unless otherwise noted, answers apply to OZPCS-RS40, OZPCS-RS40-PS and OZPCS-EP40
Any number of units may be connected in parallel but there are practical cabling and short circuit issues that must addressed for multi-PCS systems. The terminal blocks on the front of the RS40 will accommodate narrow tongue compression lugs up to 2/0 AWG. With 90°C rated cable, this limits the parallel group per cabling feed to three units – see table below. Higher temperature rated cable may permit four units to be parallel connected. Installations requiring more units may use an external combiner to parallel multiple groups. It is the user’s responsibility to ensure that acceptable cable temperatures are maintained under worst case conditions, and that the cables are adequately protected from short circuit currents from the battery and grid.
Note: Oztek offers a busbar accessory kit that may be used to conveniently connect RS40 and RS40-PS units in groups of four or less.
OZpcs-RS40 Recommended Cable Sizes
Assumptions:
- 45C ambient
- 40 LFM airflow
- 90C rated cable
| Units | Max DC (A) | AWG | Max AC (A) | AWG |
|---|---|---|---|---|
| 1 | 75 | 6 | 50 | 8 |
| 2 | 150 | 2 | 100 | 4 |
| 3 | 225 | 2/0 | 150 | 2 |
| RS40 | RS40-PS |
|---|---|
Regulates: Real or reactive AC power (grid-tied) AC voltage/frequency (grid-forming) | Regulates: DC voltage or current |
| Operates grid-tied or grid-forming | Operates grid-tied only |
Common uses: Injector absorb power to/from the local grid Seamless transfer for hybrid on-grid/off-grid applications | Common uses: Unity power factor AFE/DC supply with 4-quadrant capabilities |
| Certified to UL-1741 SA | Certified to UL-1741, but does not contain smart inverter features |
| Derives bias power from the DC source – black start from batteries | Derives bias power from the AC source – black start from grid |
The RS40 communicates only as a Modbus server. As such, it will respond to requests from a Modbus client, but cannot initiate communications. Coordination with other devices is the responsibility of an external controller which oversees the entire system.
The RS40 is a non-isolated converter. While the common-mode voltage between the AC and DC interfaces is approximately zero, one of the PCS interfaces must be isolated. When installed in a transformerless installation, the isolation is typically provided by allowing the batteries to float. If the DC supply must be non-isolated, customers must install an isolation transformer between the PCS and load.
The RS40 does not include battery charge control or cell balancing functions and is thus insensitive to battery chemistry. It has been integrated with several chemistries of lithium ion, lead acid and variants, flow cell batteries and supercapacitors.
The RS40 may also be paired with an active DC source, such as an active or passive rectifier or DC/DC converter. The DC source must have a sufficiently low impedance to ensure control loop stability and support load transients. It is recommended to consult Oztek applications’ support to ensure proper installation.
In general, the PCS fault conditions are latching and do not automatically reset – they require a fault reset command to be cleared. For this reason the PCS will not automatically clear a heartbeat timeout fault when the correct heartbeat sequence and timing is re-established.
Here are a couple of things to consider if you are having trouble resetting a heartbeat fault:
- Are you sure you have re-established the correct heartbeat sequence BEFORE you try to clear the faults? In order to clear the heartbeat fault condition, one of the following conditions must be met:
- Your very next write to the heartbeat register MUST be the previous value written +1 (or zero). If there are any gaps between the last value written (i.e. prior to the timeout error), and the new value you write, then the monitor will consider this to be an error.
- If there are gaps and hence the previous item isn’t met, then you must write to the heartbeat register at least TWICE within the timeout period (2 seconds) with the value of the 2nd write being one greater than the 1st write (or zero).
- Once you’ve verified that you have re-established the correct heartbeat sequence and timing, as described above, then verify that you are issuing the fault reset correctly. To reset the faults, you must write a “1” to register number 41122. Note that if you are correctly writing to the fault reset register but haven’t yet re-established the correct heartbeat sequence and timing described above, then the fault may be temporarily cleared but will then be re-asserted either a) upon writing the heartbeat register with a value that is not +1 greater than the previous value written, or b) immediately if you haven’t yet written to the heartbeat register since the previous timeout error.
OZIP™ Intelligent Power Modules
OZip IPM is a family of versatile, high-reliability, intelligent power modules that incorporate an IGBT power stage, gate drivers, DC Link, current and voltage sensors, and a 32-bit floating point controller. They are available in both air and water cooled configurations with either CAN or Modbus 485 communication options.
What separates OZips from other IPMs, is the inclusion of a 32-bit floating point controller and user configurable application code for inverter, motor control, and DC/DC converter applications.
Oztek’s OZIP IPM family of Intelligent Power Modules are factory programmed with one of three different applications; motor drive, DC/DC converter or AFE/GTI inverter.
The OZIP IPM based motor drive solution provides high performance and efficiency at a fraction of the cost of a general purpose industrial drive. The drive can be configured for closed loop speed or torque control using Field Oriented Control (FOC) for high performance AC induction and permanent magnet motor applications. Open loop V/Hz control is also provided for less demanding, low cost, AC Induction motor applications. A flexible control interface allows for analog, digital and serial interface options. High voltage DC Link pre-charge control logic, as well as brake control logic are provided for those applications that require them.
The OZIP IPM based DC/DC converter provides high performance and efficiency in an off the shelf solution. The interleaved buck/boost converter is a bi-directional DC to DC converter topology that can be used to convert either a low DC voltage to a higher DC voltage, or vice versa. By interleaving three converter legs with their modulators offset by 120°, the ripple current, and hence ripple voltage seen on the output is significantly reduced, due to the cancellation between phases. The bi-directional capability of the converter allows it to both source and sink current while regulating the output voltage.
The OZIP IPM based AFE/GTI solution provides high performance and efficiency at a fraction of the cost of a packaged industrial solution. The inverter can be configured to operate in AFE or GTI mode. In AFE mode the inverter regulates the DC bus voltage and can be used to power a common bus or single drive applications that require AC line regeneration and/or low harmonics. GTI mode is generally intended for renewable applications. In general there is a separately controlled DC source and the inverter is used to control real and reactive current or power to or from the grid.
Oztek does not currently support user code development and debug for the OZIP IPM power modules. Please consult the factory for volume applications.
Yes, OZIP IPMs incorporate a bootloader which allows the module to be upgraded in the field using the CAN or RS-485 interface.
OZIP IPM software includes dozens of non-volatile configuration parameters that allow the module to be easily configured for each user’s application. Please refer to UM-0056, UM-0057 and UM-0060 for application and configuration parameter details.
Yes, OZIP IPMs can be easily configured using the supplied Power StudioTM Windows GUI. The tool provides the ability to customize, download, read, and archive device configurations. It also provides a “dashboard” function with control and instrumentation capability. This allows for quick and easy integration into your product application.
Both CAN and Modbus RS-485 are available for the OZIP IPM.
Custom power converter development and qualification is time consuming and costly. Off-the-shelf solutions, if available, are typically geared more towards end-user rather than OEM requirements, and usually represent a compromise solution for the OEM. OZIP IPMs mitigate power converter development cost and risk, and eliminate substantial amounts of engineering time, while retaining configuration flexibility and the ability for you to optimize your system. While you still must qualify OZIP IPM for your application, the power module itself is already qualified at the start of the project. Once in production, OZIP IPMs high level of integration eliminates components and subsystems, reduces installation, wiring, test, and engineer support costs and simplifies purchasing and inventory management.
OZIP IPMs can be configured with one of four different cooling methods: (E) extruded fin heatsink, which utilizes natural convection. (F) fan-cooled extrusion, (H) fan-cooled crossflow and (L) liquid cooled plate.
In addition to differences between different models, output capacity is dictated by a number of application factors including:
- Maximum ambient and/or coolant temperature
- Switching frequency
- Maximum DC link voltage
- Circuit topology (in particular, DC/DC stresses are much different than motor drive or inverter stresses)
- Transient surge load and duration
- Operation duty cycle
- Product life requirements
- Model brochures provide rough sizing data for typical DC link voltage, switching frequencies, and operating temperatures. More detailed data can be found in the product user’s manuals. Oztek engineers are available to assist in model selection.
While lower frequencies are acceptable, the specified levels are at the point where conduction losses strongly dominate over switching losses. Efficiency gains for operating slower would be minimal, and audible noise would likely become more objectionable. Low switching frequencies are typically employed in motor drive applications, where the motor’s inductance provides sufficient filtering without additional size or cost. In inverter and DC/DC applications, OZIP IPM power savings needs to be balanced against increased filter inductor power loss, size and cost when considering a low switching frequency.
Higher frequency operation is limited by both power stage switching loss and IGBT gate driver capacity. Generally, models with smaller IGBTs can safely switch faster, and will have a proportionally smaller switching to conduction loss ratio, as reflected in the current capability plots. The specified max operating frequencies are practical maximums that result in reasonable power stage switching losses and safe utilization of gate driver capability. Contact the factory for applications that may require higher than specified switching frequencies.
In general, most properly applied products eventually fail due to either manufacturing or component defects, or component wear out. Ideally, manufacturing and component defects are identified and corrected before a product leaves the manufacturer, resulting in trouble-free operation until the product eventually wears out.
Continual improvements in components and assembly processes have led to fewer initial product defects industry wide, but for any given design, some residual fallout still remains. Traditionally, manufacturers of high quality products have employed burn-in to weed out this hopefully small number of manufacturing defects. While this method is still employed by many such manufacturers, the range of defects that burn-in exposes, and its efficacy as a screening tool, is quite poor by modern standards.
Oztek’s ESS process simultaneously subjects subassemblies to rapid temperature changes and electrical stresses, quickly and efficiently exposing a broad range of potential component and manufacturing defects, and it does so much earlier in the manufacturing process than burn-in. An abbreviated burn-in test is still conducted primarily to ensure full load, maximum temperature performance.
Product life and reliability are governed by both the inherent robustness of components and materials, and the margin between where the product is operated and the point where excessive stress causes failure.
Automotive grade parts are typically rated for operation over wider temperature, and undergo more stringent testing, than commercial parts. Encapsulated DC links are much more immune to environmental contamination and moisture than open stacked designs. Polypropylene film capacitors have substantially more life than aluminum electrolytic capacitors, which often limit the useful life of power electronics systems. They also self-heal if damaged by transient over voltage, and can handle much higher continuous and abnormal ripple currents without failure.
Overall, these high quality parts and construction methods mean more design margin in any application environment, which translates to higher reliability and longer life wherever the product is applied.
Running cooling fans continually at maximum speed ensures adequate thermal performance, but may result in shorter fan life, unnecessary audible noise at lighter loads, and the need for more frequent air filter cleaning/replacement. OZIP IPMs monitor system loading and device temperatures, and select a fan speed most appropriate for the particular operating conditions for more optimal behavior.
Most engineers appreciate that higher operating temperatures result in lower product life. However, temperature cycling can have an even more profound affect. Rapid temperature changes typically produce high material stresses, particularly when materials with differing coefficients of thermal expansion are tightly coupled, as they are in power semiconductor modules.
For low power electronics systems, this usually isn’t a concern, as environment temperature usually doesn’t change severely and rapidly, and self-heating is minimal. However, power electronics systems typically have considerable self-heating that can produce large and rapid temperature change, even if the ambient temperature is held fairly constant.
Special consideration needs to be given to applications with highly cyclical loads to ensure that the cooling system maintains not only acceptable maximum temperatures, but also acceptable changes in temperature. Liquid cooled systems are particularly good in this regard. Oztek engineers are available to assist in selecting the appropriate model for high cycling applications.
SCR Controllers
- Check that the SCR board is powered. When power is applied to the board the green “SYS OK” LED located around the middle of the board should be blinking.
- Check that the RS-485 cable is connected to J20 on the controller.
- If the SCR board is at the end of the RS-485 line, check that termination is enabled (jumper installed between pins 2 & 3 at J11).
- If using the ULINX RS-485/USB adapter from B&B electronics, check that the data and ground lines are connected properly and terminator attached (if at the end of the RS-485 line).
- Check that the port, baud rate and device ID are 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.
- Make sure you have selected the “Connect Communications” option in the SCC tool. See user’s manual UM-0041 for more details.
No, the OZSCR-1×00 board uses current pulse transformers for the gate drive outputs and that these are not capable of running at DC.
Yes, the LEM HAX series of current sensors is compatible with the OZSCR-1000 LEM interface.
Electrical specifications have been added to the user’s manual UM-0040. Note that the outputs are driven from a photo-coupler device from CEL, part number PS2501L-4.
The datasheet can be found at:
http://www.cel.com/pdf/datasheets/ps2501.pdf
- There are some local bias supplies generated on the board (+/-15V and +10V) – these are monitored against gross min/max expected values and if a supply is not within tolerance, this will cause a fault.
- There is a configuration memory fault that occurs if the user happens to set some combination of parameters into an illegal configuration that is not allowed by the software. If there is any suspicion that this is the cause of a fault, the user can try resetting the “Configuration Reset” command to reset all parameters back to the factory default values to see if this clears the fault. They would then have to reprogram any parameters that they had previously changed.
Oztek provides the “OZSCR-1×00 SCC Tool” (SW90142) GUI for the OZSCR-1×00 boards. It is available for free and can be downloaded from our website. This tool lets the read and modifies the various configuration parameters for the control board, as well as to update the firmware on the control board.
Yes, the OZSCR-1000 is compatible with a 208 VAC mains voltage source.
Yes, the controller can handle all three applications. You’ll want to configure the controller similar to what’s shown in UM-0040, figure 13. For half-controlled and full-controlled bridges you can use a pot or external control voltage to adjust the firing angle, and the fast inhibit input to enable operation. Alternatively, you can set the command angle to maximum, and use the soft inhibit input to enable the operation and slew the firing angle. For static switch testing, set the angle to 100%, and use the fast inhibit input to enable operation.
The OZSCR-1×00 can be used as a simple soft start controller by operating in open-loop phase angle control mode – in which case no current feedback is necessary. The phase command needs to be set to the max (for full conduction) using either the analog input pin or using Modus register control and setting the default phase command register. The user then needs to configure the soft inhibit control parameters to set the soft-start ramp rate to the desired value for the application.
CAN Bootloader Software
- 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).
- 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.
- The bootloader uses the DSP’s CAN-B peripheral on GPIO20/GPIO21 to interface to the CAN bus.
- The bootloader code derives the SPI EEPROM and CAN serial bit timing assuming the DSP is driven with a 30MHz external clock source.
Yes, upon purchase, customers receive all of the source code required to build the bootloader executable image. This allows them to make changes to the way in which the bootloader operates, as well as targeting the source code for another microprocessor.
As written, the entire bootloader is intended to execute out of RAM memory, leaving the entire FLASH available for application. As such, on our own boards, we store the bootloader in an external SPI memory, although this is not a requirement, and the DSP is configured to “boot from” SPI EEPROM. This causes the DSP to load the custom CAN bootloader into RAM from the EEPROM following a POR or a S/W reset.
The bootloader source code could be modified such that it resides in a protected portion of FLASH, and is used to program the remaining application portion of FLASH.
Inverter Control Boards
Unless otherwise noted, answers apply to OZDSP-3000, OZGTI-3000, OZBST-3000 and OZMTR-3000
The OZDSP-3000 is an inverter control board that is intended for customers who wish to write their own application software. Oztek also provides the OZDSP-3000 pre-configured with software for a variety of power control applications including grid tie inverters and active front ends (OZGTI-3000), voltage mode inverters (OZVMI-3000) and boost converters (OZBST-3000).
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.
Yes, source code license are available for the OZGTI-3000 application software. Both restricted and unrestricted licenses are available as described below.
Restricted source code license – includes source code and Simulink system simulation model.
The restricted source code license grants the licensee nonexclusive, nontransferable, perpetual, worldwide right to:
- Use and reproduce as many copies of the source code and system simulation model as are reasonably necessary for the purpose of generating executable code to run on Oztek supplied control hardware;
- Modify and create derivative works of the source code for the purpose of generating executable code, solely for use on Oztek supplied control hardware.
Unrestricted source code license – includes source code, Simulink system simulation model, and hardware design files (schematic, bill of materials, PCB Gerber files).
The unrestricted source code license grants the licensee nonexclusive, nontransferable, perpetual, worldwide right to:
- Use and reproduce as many copies of the source code and system simulation model as are reasonably necessary for the purpose of generating executable code to run licensee’s control hardware;
- Modify and create derivative works of the source code for the purpose of generating executable code to run licensee’s control hardware.
The INV_IOUT signal is a +/- 10V signal into the OZxxx-3000 board representing the full scale output/input current. The scaling can be whatever makes sense for your application – you just need to program the corresponding full scale value (i.e. what current is represented by 10V on the input pin) into the applicable configuration parameter. For example PID 0x0022 “INSTR_CURR_FS”, “Motor Phase Current Measurement – Full Scale” is used to scale this input on an OZMTR-3000 controller.
Our AFE user’s manual (UM-0021) has a section that describes the SKiiP power module interface (section 3.1.1) as well as a subsection that discusses the expected signal levels for any user who want to make their own non-SKiiP power modules look like a SKiiP-like interface to our control board (section 3.1.2). We do have users that have done exactly this – they use our standard AFE controller with Infineon modules and they have made their own interface board to connect the OZxxx-3000 to their power stage.
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-cycle 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. Assuming 30Vpk is dropped across the filter components, the required minimum DC link voltage is given by (747+30)/0.92 = 845V.
