Diesel-electric drive solutions for utility vehicles: Technology and application examples
In diesel-electric drive systems, 100% of the energy is generated from internal combustion engines. The mechanical energy generated by an internal combustion engine is converted into alternating current by a generator, which means that diesel-electric propulsion systems are, strictly speaking, their own power stations. A rectifier then converts the alternating current into direct current before an inverter converts this into an alternating current with a variable frequency and an adjustable amplitude. This current conversion process is necessary since the subsequent electric motor, which ultimately drives the wheels, would otherwise always run at the same speed. Sometimes a battery is also installed that is continuously charged by the internal combustion engine. The power transmission from the electric motor to the wheels or the propeller in ships is effected either directly or indirectly by the interconnection of a gear box.
When electrical drive systems are implemented, preference is given to three-phase generators combined with three-phase asynchronous motors and electronic power components such as IGBTs. The advantage is that the current frequency can be adapted to the particular driving situation by the inverter (for example VECTOPOWER from ARADEX), which increases efficiency and reduces costs.
Advantages and disadvantages
The appeal of diesel-electric propulsion systems is that they combine the advantages of internal combustion engines and electric motors. Energy generated by internal combustion engines makes it possible to achieve long ranges, while electric motors can compensate for the significantly lower efficiency levels of combustion engines under partial load. For this purpose, a separate combustion engine has to be disconnected in the system during partial load operation. The inverters supply the required amount of energy to the electric motor, which has extremely high efficiencies in the partial load range.
Although the drive train, which contains a number of current conversions, is also affected by losses, diesel-electric drive systems use approximately 20-30% less fuel than pure diesel drive systems. The purchasing costs are below those of fully electrified drive systems, since no battery or only a smaller battery has to be financed – however, the fuel savings are also lower, since diesel is still needed. If a battery (or a supercapacitor) is installed, the efficiency is further increased by recuperation of the brake energy.
The transmission of power can be controlled electronically, so that hardly any shocks or jolts occur during start-up and braking, which is particularly convenient for vehicles used for passenger transport. Although numerous components have to be purchased, diesel-electric propulsion systems usually pay off after a few years due to the increased energy efficiency.
Since the advantages of diesel-electric drives can only be realized when several combustion engines are interconnected, this electrification variant is particularly suitable for large mobility solutions, e.g., ships, trains, or dump trucks.