Electrical Propulsion System for Aviation – Experimental Validation of Efficiency Improvements

This paper deals with electrical propulsion system for light airplane or paraglider. The electrical drive consists of electrical motor, frequency converter and the batterypack. Electrical motor used in a light paraglider was designed as a permanent magnet synchronous motor (PMSM) in the Research and Development Centre of Electrical Machines KOMEL, Poland. Parameters of the motor, frequency converter and battery pack were shown. In this article, an influence of different propellers (1 fixed, 2 adjustable) and results of laboratory test was described. For increasing the efficiency of the electric propulsion, influence of switching frequency of the converter were tested and presented. The results of laboratory test were discussed.


Introduction
Aviation waits for environment friendly drives and propulsion systems. This paper deals with electrical propulsion for a light airplane or paraglider which was shown in Figure 1.

Electric motor
Parameters of the electric motor type SMwsK90L-8 are shown in Table 1. Electrical motor was designed as an interior permanent magnet synchronous motor (IPM), air cooled, 25 kW, frame size 90 mm. The rotor of the motor has a special slots for magnets. Cross electromagnetic circuit of electric motor is shown in Fig. 3. Electric motor mounted in paraglider with the propeller is presented in Fig. 4 The eight radially magnetized permanent magnets type NdFeB are built into the rotor core. The electric motor was put in the specially designed alluminium frame which has special air duct (Fig. 4).
International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium esigned propulsion system was mounted in s trike. Light two person paraglider is able to fly for about 25 minutes with two persons and almost 1 hour with one person. The electric motor can be turned off during the flight what arameters of the electric motor type 8 are shown in Table 1. Electrical interior permanent magnet synchronous motor (IPM), air cooled, 25 kW, frame size 90 mm. The rotor of the motor has a special slots for magnets. Cross section of electromagnetic circuit of electric motor is shown in Fig. 3. Electric motor mounted in paraglider with the propeller is presented in Fig. 4

Battery Pack and frequency converter
Electric drives for light airplane or paraglider needs the special accumulator. technology, the optimal solution is lithium lithium -polymer. The battery pack has a special management system (BMS) which parameters of the cells like temperature and voltage of each cell, process of charging and discharging battery, and balances the cells etc. Parameters of the battery pack are presented in Table 2. The battery pack mounted in paraglider is shown in Fig. 5. The battery pack has spec provides cooling during operation 2 The frame of electric motor mounted in paraglider ack and frequency Electric drives for light airplane or paraglider needs the special accumulator. According to solution is lithium -ion or The battery pack has a special management system (BMS) which monitors cells like temperature and voltage of each cell, process of charging and balances the cells etc. ry pack are presented in . The battery pack mounted in the paraglider is shown in Fig. 5. The battery pack has special air duct, which operation. In the electrical propulsion intended for light airplane or paraglider the special frequency converter was used. MOSFET SKAI module, manufactured by SEMIKRON, works supplied from the lithium -ion battery pack. Parameters of the frequency converter, which was mounted in paraglider under the electric motor {fig4}, are presented in Table 3.

Optimization process
During the optimization process influence of 2 aspects (phases) on the efficiency of the particular components, i.e on efficiency of the motor and frequency converter separately, as well as on efficiency of the whole drive (motor + converter) were investigated: First phaseswitching frequency of the converter -adjusting of the switching frequency changes switching losses in the converter and the additional losses in the motor. Second phase -propellers -3 different propellers (1 fixed, 2 adjustable) were used and tested. The examinations process of an influence of switching frequency on the efficiency, two switching frequencies -10 kHz and 15 kHz were set in the converter. According Efficiency map for 10 kHz switching frequenc (inverter+motor) is shown in figure 9 highest efficiency of the propulsion system is obtained at the range of rated torque between 20 to 60 Nm and rotational speed between 1900 to 2400 rpm. The very similar situation, like in case of figure 9, is for 15 kHz switching inverter and motor {fig10}. The area with highest efficiency appears for 20 to 60 Nm and rotational speed between 1800 to 25 After performing the first flight, which provided many data needed for further research, an influence of different propellers (1 fixed, 2  figure 9. The highest efficiency of the propulsion system is obtained at the range of rated torque between 20 speed between 1900 to The very similar situation, like in case , is for 15 kHz switching frequency for . The area with highest efficiency appears for 20 to 60 Nm and ational speed between 1800 to 2500 rpm. ght, which provided many data needed for further research, an influence of different propellers (1 fixed, 2 adjustable) was investigated. Results presented in figure 11.
The fixed Helix propeller has l remaining examinated propellers but it is also lauder. The fixed Helix propeller has two blades and it is not adjustable. The two remaining investigated propellers have three adjustable blades. The angle of three-bladed propellers w set to reach thrust of 100 KG speed. The electric paraglide during two persons flight. The course of output power taken from battery during the flight was presented in figure 12. During the two persons flight minutes, 2.6 kWh energy were used. pilot and passenger was 90 an

Conclusion
As can be recognized from figure 7 motor at the 15 kHz switching frequency efficiency higher than 90% in range operation between 15 to 70 Nm motor controlled with 10 kHz situation is very similar. The efficiency is above 90%. The difference of efficiency in whole range operation torque for converter {fig.9} is more visible. The highest efficiency of 10 kHz switching frequency, The fixed Helix propeller has larger thrust than remaining examinated propellers but it is also lauder. The fixed Helix propeller has two blades and it is not adjustable. The two remaining investigated propellers have three adjustable bladed propellers was t to reach thrust of 100 KG at maximal rotation electric paraglider was tested in air The course of output power taken from battery during the flight was from battery during the two persons flight flight which had about 25 minutes, 2.6 kWh energy were used. The weight of nd 60 KG.
can be recognized from figure 7 the electric witching frequency has the % in range of torque between 15 to 70 Nm. In case of electric kHz switching frequency, situation is very similar. The efficiency is above The difference of efficiency in whole range operation torque for converter {fig.9} is more The highest efficiency of the inverter is for , but from figure 8 it 7 8 9 10 11 12 13

Time of Flight, [min]
can be noticed that there is no differences between characteristics of the efficiency vs. load torque for 10 and 15 kHz switching frequency if the whole propulsion system is investigat From examinations done and received results ( Fig. 9 and 10, efficiency maps), it the area with highest efficiency is practically the same for two examined cases (10 and 15 kHz switching frequency). The range of torque and rotational speed (for highest efficiency) do not change, even for different switching frequency. After adjusting switching frequency, distribution of losses can be changed. second phase of investigations proved that propellers have higher impact factor into efficiency level of the drive than frequency. The fixed Helix propeller has a better coefficient (Thrust/Power) than two remai examined propellers (Fig.11). The Fixed Helix propeller produce higher thrust (in range 1800 to 2400 rpm) with smaller power demand than Peszke and Helix adjustable three propellers. Producing the higher thrust by Fixed Helix propeller (in range 1800 to 2400 rpm Fig.10) causes higher noise level. electrical propulsion system mounted in paraglider was tested in air as well. fly environment friendly with no pollution and no danger of flammable fuel. The nois system is lower than the combustion engine drive, what is very important as well.
that there is no differences efficiency vs. load torque for 10 and 15 kHz switching frequency if the whole propulsion system is investigated. From examinations done and received results , efficiency maps), it can be seen, is practically the (10 and 15 kHz . The range of torque and rotational speed (for highest efficiency) do not change, even for different switching frequency.
adjusting switching frequency, only the ribution of losses can be changed. The phase of investigations proved that the ellers have higher impact factor into efficiency level of the drive than the switching fixed Helix propeller has a better than two remaining ). The Fixed Helix propeller produce higher thrust (in range 1800 to 2400 rpm) with smaller power demand than Peszke and Helix adjustable three-bladed . Producing the higher thrust by Fixed eller (in range 1800 to 2400 rpm - Fig.10) causes higher noise level. The whole electrical propulsion system mounted in paraglider was tested in air as well. It enables to fly environment friendly with no pollution and no danger of flammable fuel. The noise of the system is lower than the combustion engine drive, what is very important as well.