DC/AC Drives

The use of frequency converters to run induction motors brings many advantages:

  • The speed can be controlled and thereby the efficiency can be increased for fan and pump systems.
  • The motor start is controlled which limits the starting current.
  • Start and stop times can be adapted to suit the load.

Normally a frequency converter is designed to have an AC input. When the main power source is DC, e.g. in submarines, conventional frequency converters cannot be used. To satisfy this need, the DC/AC converters of the NEDA type are designed to work with a DC input. The input voltage is allowed to vary over a broad range to enable a battery to be the feeding source. Today you can get NEDA converters for the voltage ranges 200-420VDC and 540-830VDC.

The NEDA converters use processor based technology to create three phase PWM signals (Pulse Width Modulation). These signals control the output bridge, which is built up with IGBT transistors (Insulated Gate Bipolar Transistor). The transistor current is continuously supervised and the converter is fully short-circuit and earth-fault protected without fuses.

Important considerations in the design of the converters have been reliability and performance. The NEDA converters are designed to meet military EMC requirements. The cabinet is designed for a tough environment. Smaller units are air cooled, while the larger ones normally are equipped with water-cooling.

By using a NEDA type DC/AC converter the following features can be obtained:

  • Possibility to operate a standard three-phase induction motor from a DC network
  • Speed control over the whole speed range
  • Possibility to avoid critical speeds (eliminating noise problems)
  • Built-in soft start, no high starting current
  • Built-in overload protection
  • Adjustable acceleration time
  • Adjustable deceleration time
  • Short-circuit and earth fault protection without fuses
  • HF tight cabinet

NEDA converters have been delivered since 1987 and more than 165 units have been delivered. A brief summary of the submarine projects where NEDA converters are used:

  • SOR/Challenger, about 30 units
  • Näcken/Kronborg, 4 units
  • Västergötland, about 30 units
  • Gotland, about 30 units
  • New production HDW submarines for Greece, 8 units
  • New production HDW submarines for South Africa, 6 units

The NEDA converter models presented in this homepage are all originally designed for a certain purpose. Converters for other power and voltage ranges can be designed according to your requirements.

Nöjdhs Elektronik AB, Box 1342, S-251 13 Helsingborg, SWEDEN   Phone: +46 42 38 16 00   Fax: +46 42 13 63 50   E-mail: mail@nojdhselektronik.se