Page - 106 - in Hybrid Electric Vehicles

to the safety (direction, breaking, lights, distance sensors, mirrors etc.) or to the comfort (seats, HAVC, audio, navigation display etc.). At the same time, a lot of traditional mechanically driven loads are replaced with electrical driven ones (water pumps, servo steering, ventilation fan, etc.). This demand of electrical energy, of around 10 kW [5], requires increasing generator power and a certain level of efficiency (normally situated at 40–55%) [6]. A common alternator in a car is relatively cheap and with low efficiency, but with the expected increase of power, it exceeds the capability of the Lundell generator (claw pole synchronous machine). In this context, the replacement of classical alternator with a high efficiency machine is mandatory. Besides this, the operating mode of the conventional starter (around 1 s for each start) is used only for the start of the ICE and after it becomes an extra weight in the vehicle. The easy (costs and implementation) solution of this problem is to replace both machines (starter and alterna- tor) with a single electrical machine. The initial concept of the integrated starter-alternator (ISA) system was developed in order to gain more space for the powertrain system and to reduce the weight of the vehicle by combining the starter with the alternator. This system ensures the start/stop of the internal combustion engine and the supply with electricity of all the auxiliary subsystems (safety or comfort). Especially in parallel configuration of HEV, the ISA is used for starting the internal combus- tion and supply the electrical load. A second electrical machine is necessary for the electric propulsion. The method for the simplification of this structure involves the use of a single electric machine comprising three operating modes: starter-alternator and booster. In this case, the integrated starter-alternator-booster (ISAB) system will be able initially to start the ICE, then, when it is turned on, it will reverse to generator mode and will supply electricity to consumers and the storage system. By adopting adequate control strategies, the electrical machine is capable of moving quickly from generator to motor (booster) and back in order to help the international combustion engine for a short period of time (maximum 2–3 min), if more power is necessary (overruns, ramp, curbs, etc.) [7]. This operating mode of the machine is generically called integrated starter-alternator-booster (ISAB). Using ISAB in parallel HEV is generically called Mild-HEV. In this configuration, the full electric propulsion of the vehicle is not possible, but the production costs necessary for the implementation of the hybridization in conventional vehicles are lowest compared to other variants of HEV. According to Ref. [8], where the influence of fuel consumption for a small car equipped with ISAB is investigated and considering the European standard (1999/100 EC), the fuel consump- tion is reduced to about 12% in total. The increase in the number of electric components within the vehicles boosts the market for electrical motors for hybrid and electric vehicles. A Frost & Sullivan market research finds that the market earned revenues of about 55 million Euros in 2010, which are expected to reach $1.6 billion by the end of 2017 [9]. The required characteristics of the ISAB in the starter mode and alternator (generator) mode are very restrictive for a conventional electrical machine [10]: Hybrid Electric Vehicles106