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Motor and Drive

 

Blog: Build your own Hangglider and Paraglider Winch

Design of motor

The graph shows the charateristics of and induction motor at nominal current.

As we want do utilize the motor as much as possible, the motor can be overloaded with up to 180% of the nominal torque.

Paraglider and hangglider winches operates only up to slightly above the base speed, as the peak power is dramatically reduced above the base speed.

Thermal overload is not a problem, as the duty cycle of the motor is low. A tow takes about 3 minutes and before the next pilot is ready 3-10 minutes has typically past.

One more technique to get more power of an industrial motor is to use a motor with a 230/400V winding and use 87Hz-technique. It simply means that you couple the motor in delta-connection and supply it with 400VAC and 87Hz instead of 50Hz.

 

By using this technique the torque at 87Hz is heavily increased without stressing the motor.

 

Read more about this right here:
https://vesselautomation.com/scalar-control-of-vfds-87-hz-characteristic/

 

A standard Siemens 4-pole motor can handle up 4200 rpm, and 5600 rpm with improved bearings, so it is no problem to operate above 50Hz from a mechanical perspective.
A standard 6-pole can handle up to 3600 rpm according to the datasheet.
However, even with 87Hz-technique, is not desirable to operate above 120Hz, as the peak power is reduced.

The table shows some examples of different motor configurations and their performance with a Ø129mm drum.

The “Utility factor” is the product of “overspeed factor” times “overload factor”. This value should not be more than 2-2.5 depending on the overspeed factor, as this is the physical power limit of an induction motor.

Overspeed factor 1.0: Utility factor < 3

Overspeed factor 1.1: Utility factor < 2.8

Overspeed factor 1.2: Utility factor < 2.6

Overspeed factor 1.3: Utility factor < 2.5

Overspeed factor 1.4: Utility factor < 2.3

Overspeed factor 1.5: Utility factor < 2.1

Overspeed factor 1.6: Utility factor < 1.9

Overspeed factor 1.7: Utility factor < 1.7

Overspeed factor 1.8: Utility factor < 1.6

Overspeed factor 1.9: Utility factor < 1.4

Overspeed factor 2.0: Utility factor < 1.2

 

These numbers yields as long the battery voltage at load is above the nominal voltage, which is 570VDC*

Read more about the optimal battery voltage in the chapter battery.

 

Most optimal choice would probably be the “5,5kW 6-pole motor” connected for 87Hz and 400VAC.

 

*Reference: Siemens motor catalog (Tb/Trated)

The mechanical dimension are the same for all the motor configurations above, as they are standard norm motors. Only the length differs.

See mechanical drawings here:

5,5kW 6-pole motor
7,5kW 6-pole motor
7,5kW 4-pole motor
11kW 4-pole motor

Choice of frequency converter

Long story short… There are two types of frequency converters:
– Converters for pumps and fans
– Converters for conveyors, cranes or mills

 

The first type is more common, the second type is what we like, because it has a lot of nice features, as it is designed for demanding applications.

 

However, the important part is that the frequency converter has a “torque limitation”. This allows to limit the torque, which is propotional to the tension in the line.

 

It is very beneficial if the converter also allows closed-loop operation, because the torque accuracy becomes better in the very low end (0-20 kg). This is important for hanggliders that starts from a start trolley, as it begins to roll if the tension is more than 10-15 kg.

 

The “ATV61” from Schneider is build for pumps but still provides torque limitation. But the newer generation from Schneider “ATV600” build for pumps does not.

“Power limitation”, or the very common “current limitation” does not work.

ATV61 and ATV600 does not allow closed-loop operation.

 

The ATV71 and the newer generation ATV900 does both provide torque limitation and closed loop operation.

ATV320 does provide torque limitation but not closed-loop operation.

 

You just have to google the manual of the drive, and see if it provides torque limitation.

 

There are many brands producing frequency converters. Use the big brands as the algorithms in these provides the best performance, i.g. Schneider-Electric, Siemens, ABB, Danfoss, etc.

The frequency converters VLT FC301 and FC302 from Danfoss does also provide torque limitation and closed-loop operation.

 

The size of the converter should fit the motor and be able to provides sufficient current to generate the desired torque. See the table in “Design of motor”.