BMA Technology is proud to present the hybrid propulsion concept combining features of a diesel mechanical system and a diesel electric plant. In its most basic form the configuration consists of a diesel engine connected directly to a synchronous machine which drives the propeller. The synchronous machine can operate both in generator mode and in motor mode and is controlled by a frequency drive. This gives the possibility for Power Take Off (PTO) mode or a Power Take In (PTI) mode.
In the traditional fixed-speed shaft generator system, the shaft generator is driven by the ship’s main engine which is also driving the propeller. In this solution, the ship main network frequency is totally dependent on the diesel engine speed, and thus the propeller speed. Any change in speed has a direct impact on network frequency. Therefore thrust and ship speed can only be controlled by propeller pitch, leading to unoptimized loading of the main engine, decreased efficiency and increased COx and NOx emissions.
The PTO function can easily be extended to a combined PTO/PTI mode when a variable frequency drive is installed between the electrical distribution system and electrical machine by allowing the machine to operate either as a motor or generator.
A shaft generator frequency drive (SGFD) allows a wide speed range for the main engine. Propeller pitch and main engine speed can always be optimized for any desired sailing speed. The BMA Drive software makes sure that the system maintains a stable voltage and frequency regardless of the main engine speed.
When a frequency converter is installed between the shaft generator output and the electrical distribution system, the shaft generator can be used independently regardless of the shaft speed, enabling optimization for each operating condition. The BMA Drive is in constant communication with the PMS software allowing the shaft generator to run in parallel with the auxiliary generators. Furthermore the software has a proactive approach to prevent blackouts by monitoring the conditions/commands in the system.
This means that the full benefits of lower specific fuel oil consumption (SFOC) for the main engine compared with the auxiliary engine can be fully exploited. If the auxiliary engines use marine diesel oil (MDO) instead of heavy fuel oil (HFO), the difference is even greater: the costs of lubrication oil and maintenance are relatively higher for auxiliary engines than for main engines.
THE BMA Drive is EMC certified and complies fully with THD requirements of the major class societies.
PTO (island and parallel modes)
In power take-off (PTO) operation, the shaft generator operates as a generator. The SGFD can operate in island mode (single generator) or in parallel mode with other auxiliary generators.
SGFD uses droop control to adjust voltage and frequency when operating parallel with other generators. The SGFD is seen as one of the generators in the system.
In addition to basic features, the shaft generator drive includes extra functionality. The SGFD can compensate unbalanced loads in the grid and also provides reactive power compensation.
PTI and PTH (Electric and Hybrid Modes)
In power take-in (PTI) operation mode, the shaft generator functions as a motor. The power is taken from auxiliary engines and the SGFD operates the motor.
The take-me-home (PTH) feature can be used if the main engine has malfunctioned. The main engine can be decoupled from the shaft line so that the shaft generator can operate independently.