All Three Phases under Control

In the “Kazan” proprietary project, IAV is working on a variable-power, universal inverter with unbalanced-load capability – e.g. for bi-directionally connecting vehicle electric system and 230-V low-voltage systems. One of the key parts is a controller board for actuating the components of the inverter system. Given its high performance, it permits fast, precision control intervention, e.g. for correcting different loads on the three phases.

The junction between different power supply systems is becoming increasingly important in the context of electric mobility and renewable energies. When charging the electric car’s high-voltage battery from the domestic power outlet, an inverter must convert the 230 volts of alternating current in a direct-current voltage (often of 400 volts). In future, vehicle batteries are also to act as buffers for green electricity currently not needed and feed it back into the public power grid – in this case the inverter must work in the opposite direction and generate 230 V AC from the DC voltage in the vehicle. Very similar tasks occur with renewable energies where electric power from photovoltaic systems flows to solar batteries or into the domestic electric system.

The system IAV has developed consists of a power supply unit, various inverters and a controller board. The modular inverter platform can be matched to the voltage class (by changing an assembly) and to the required power level (parallel connection of several devices). It also provides an option for realizing chargers and drive inverters. “The platform is not only suitable for connecting electric vehicles with external systems”, reports Dr. Andreas von Daake, development engineer for control units at IAV. “We can also use it, for example, to connect the IAV Energy Container to an electrolyzer.”

The central component is the controller board for controlling the inverter system’s individual components, including power inverter, AC mains filter and buck/boost converter. It is based on a high-performance, 300-MHzclocked AURIX TC299 tri-core microcontroller from Infineon which, with its ten delta-sigma analog/digital converters in addition to the successive-approximation ADC (analog to digital converters), permits precision measurement of all relevant signals. “This is necessary in particular for the high-resolution control interventions for actuating the IGBT power transistors which are clocked and controlled at 90 kHz”, von Daake says. A large number of interfaces, for example, permits connection to vehicle electric systems (via CAN or FlexRay) and the parallel connection of several boards (via Ethernet). Developers attach tremendous importance to safety, fault documentation and detailed data logging for which a dedicated SRAM is available (it records the measured and controlled variables from the last 20 seconds).

Eine Vielzahl von Schnittstellen ermöglicht beispielsweise den Anschluss an Fahrzeug-Bordnetze (via CAN oder FlexRay) und die Parallelschaltung mehrerer Boards (via Ethernet). Großen Wert legen die Entwickler auf die Sicherheit, die Protokollierung von Fehlern und das ausführliche Datenlogging, für das ein eigenes SRAM zur Verfügung steht (es zeichnet die Mess- und Stellgrößen der letzten 20 Sekunden auf).

“For the controller board, we have opted for a solution developed in-house because this gives us full access to the software and lets us match it to our requirements without any constraints”, von Daake reports. “Given the challenging nature of the control tasks involved, this is very important.” For instance, providing full compatibility with unbalanced loads is part of the controller board’s control tasks – a feature that does not come with devices available on the market and one that is important in the context of photovoltaic systems. Because of its compatibility with unbalanced loads, the controller board can compensate for any unbalances on the three phases without any costly interventions in the grid.

The controller board will be ready for use from October 2017, the entire modular system is to be available at the end of 2019 and then be offered as an IAV product.

• Microcontroller:
  Infineon TriCore AURIX TC299 (32 bit, 300 MHz, 3 cores)
• Interfaces:
  4 x CAN, CAN-FD (up to 5 Mbit/s, wake-up capable, electrically isolated), Ethernet, LIN, 2 x SPI, SD card, 2 x I2C, EBU, USB
• JTAG, DAP, HSCT
• 10 analog inputs (4 DC inputs, 6 AC inputs)
• Driver control:
  3 x 3-level module (inverter)
  2 x 2-level module (buck/boost converter)
  6 x 2-level module (resonant converter)
• Memory for faults as well as measured and controlled variables