The possibility of increasing the energy of motor recovery during mechanical braking of its shaft
The article considers the possibility of increasing energy savings during mechanical deceleration of the motor shaft. The results of the experiment showed that the energy efficiency in a new designed design of an electric motor with a rotating stator during mechanical braking is 2.5 times greater than in a similar electric motor with a static stator.
It is known that the electric motor during braking can generate electricity. Such braking is widely used in electric vehicles, trams, trolley buses, electric trains, trains, as well as in centrifuges and in lifting and transport equipment (cranes, lifts, elevators), etc., but the amount of generated electricity in mechanical brake modes is relatively small .
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Diagrams characterizing one of the modes of energy recovery, together with a mechanical (friction) brake, for a hybrid. The schedule is taken from here .
It was noted that the stator of the engine can rotate when braking, if given the opportunity for it, for example, put in the bearing. The idea came to use the energy of such a rotating stator, i.e. here the rotor stopped due to mechanical braking will act as the stator, and the rotating stator, as the rotor. The conditional image of this process is shown in the video, first the conditional rotor rotates, with the load on the shaft, then the conditional stator:
Naturally, to achieve the right moment on the shaft, its stator must be static. The speed of rotation of the stator, with mechanical braking, will depend here on the moment reached on the shaft, the moment of inertia of the stator itself and the moment of friction, on which the rotation of the stator depends. Those. The formula that describes the rotation of the stator should look like this:
- angular (rotational) stator acceleration
- angular (rotational) acceleration of the shaft before braking
- moment of stator inertia
- shaft moment of inertia
- friction torque acting on the stator rotation
We describe in more detail the experiment. An experimental setup was made:
It consisted of a portable platform on which an electric motor was attached, brakes and measuring instruments. For an electric motor with excitation from permanent magnets, with a power of 250 W, an adapter was made from a PCB, into which a steel stud was screwed, the stud was inserted into a housing bearing, the adapter allowed the stator to rotate in the bearing when braking the motor shaft, and for further comparisons, leave the static stator, with the help of the inserted stop.
An aluminum disc with a diameter of 300 mm and a thickness of 10 mm was attached to the motor shaft, in turn, a manual mechanical brake was installed.
During mechanical braking, the energy of recovery was fed to a dual-channel USB-oscilloscope PCS 250, the oscilloscope gave the value of this energy to a computer.
To measure the energy, from the installation to the second channel of the oscilloscope were connected several resistors with resistance of 1 Ω, power of 20 and 100 W, connected in parallel to each other, which served to calculate the current in the circuit.
Data recording energy recovery during mechanical deceleration of the shaft, conducted in two modes, with a non-rotating stator and a rotating stator. For these two modes, the same maximum disk rotation frequency interval was selected, at which the data of the experiment was recorded, this interval was from 500 to 600 rpm. A total of 12 measurements were made for each mode.
As a result, 8 measurements for each mode were taken for processing. For the arithmetic mean value of the maximum speed of the shaft before braking, for the two modes were approximately the same.
With the help of the calculation of the standard deviation (for each mode separately), the results of the recovery energy obtained, which do not fall within the confidence interval, were eliminated.
For a rotating stator, the arithmetic average was 558.5 (rpm), for a static stator 559.1 (rpm).
The arithmetic average value of the energy recovery during mechanical braking for a rotating stator was 5.3 J, for a static stator 2.04 J.
The number of tests and the amount of energy received for the two modes
It is worth paying attention to the nature of the polarity of the energy being recovered during mechanical braking, the voltage in the electric motor reversed its polarity:
And in a design with a static stator, the voltage did not change its polarity:
The figures shaded area of mechanical braking. One cell on the waveform for t (time) is 200 ms, for U (voltage) is 0.2 V.
To use the energy of reverse polarity, you can use a polarity switch for this purpose.
It is also worth noting that recovery with a rotating stator in the mode without mechanical braking will be less, so the "turn on" rotation of the stator before mechanical braking should be as minimal as possible, but sufficient for the rotational energy from the rotor to transfer to the stator. Judging from the oscillograms, a time of about 100 ms was sufficient, and in this period of time no significant losses are visible, it is likely that the time to a mechanical brake can still be reduced. There were ideas to make a second static stator over the rotating stator, in order to reduce losses during non-mechanical braking, but this would complicate the design of the electric motor.
Prior to this development, there was a design with a series-excited electric motor, in which the stator also rotated, with mechanical braking of the shaft.
Conclusion: In the experimental design of the engine with mechanical braking of the shaft with a rotating stator, the energy of recovery is 2.5 times greater than with a static stator, which clearly illustrates the possibility to increase the energy saving of electric motors in mechanical braking modes. The amount of energy recovery here will be more than the torque of rotation of the shaft before braking and the smaller the friction torque of the rotating stator, as well as its moment of inertia allowed for the stator to rotate, and the smaller the torque of the shaft and more of the rotating stator friction, etc. the energy of recovery will be less, i.e. in spite of the effect obtained, it is worth asking about the payback and reliability of design changes for a device in which an electric motor can be used with such an effect.
Project management: Julian Baryshnikov (designing, assembling, conducting an experiment, making parts, writing an article, an idea) - iulianbaryshnikov@yandex.ru
Project assistance: Vitaly Azarov (design, assembly, experiment), Anton Alyoshkin (design, assembly, parts manufacturing), M.V. Yakovitskaya (edited by the article), Alexander Troitsky (conducting an experiment), Nikolai Eremin (software for measuring instrument), Alena Chumak (design), FabLab Polytech SPb (manufacturing of parts, measuring instrument, conducting an experiment).
It is known that the electric motor during braking can generate electricity. Such braking is widely used in electric vehicles, trams, trolley buses, electric trains, trains, as well as in centrifuges and in lifting and transport equipment (cranes, lifts, elevators), etc., but the amount of generated electricity in mechanical brake modes is relatively small .
')
Diagrams characterizing one of the modes of energy recovery, together with a mechanical (friction) brake, for a hybrid. The schedule is taken from here .
It was noted that the stator of the engine can rotate when braking, if given the opportunity for it, for example, put in the bearing. The idea came to use the energy of such a rotating stator, i.e. here the rotor stopped due to mechanical braking will act as the stator, and the rotating stator, as the rotor. The conditional image of this process is shown in the video, first the conditional rotor rotates, with the load on the shaft, then the conditional stator:
Naturally, to achieve the right moment on the shaft, its stator must be static. The speed of rotation of the stator, with mechanical braking, will depend here on the moment reached on the shaft, the moment of inertia of the stator itself and the moment of friction, on which the rotation of the stator depends. Those. The formula that describes the rotation of the stator should look like this:
- angular (rotational) stator acceleration - angular (rotational) acceleration of the shaft before braking - moment of stator inertia - shaft moment of inertia - friction torque acting on the stator rotationWe describe in more detail the experiment. An experimental setup was made:
It consisted of a portable platform on which an electric motor was attached, brakes and measuring instruments. For an electric motor with excitation from permanent magnets, with a power of 250 W, an adapter was made from a PCB, into which a steel stud was screwed, the stud was inserted into a housing bearing, the adapter allowed the stator to rotate in the bearing when braking the motor shaft, and for further comparisons, leave the static stator, with the help of the inserted stop.
An aluminum disc with a diameter of 300 mm and a thickness of 10 mm was attached to the motor shaft, in turn, a manual mechanical brake was installed.
During mechanical braking, the energy of recovery was fed to a dual-channel USB-oscilloscope PCS 250, the oscilloscope gave the value of this energy to a computer.
To measure the energy, from the installation to the second channel of the oscilloscope were connected several resistors with resistance of 1 Ω, power of 20 and 100 W, connected in parallel to each other, which served to calculate the current in the circuit.
Data recording energy recovery during mechanical deceleration of the shaft, conducted in two modes, with a non-rotating stator and a rotating stator. For these two modes, the same maximum disk rotation frequency interval was selected, at which the data of the experiment was recorded, this interval was from 500 to 600 rpm. A total of 12 measurements were made for each mode.
As a result, 8 measurements for each mode were taken for processing. For the arithmetic mean value of the maximum speed of the shaft before braking, for the two modes were approximately the same.
With the help of the calculation of the standard deviation (for each mode separately), the results of the recovery energy obtained, which do not fall within the confidence interval, were eliminated.
For a rotating stator, the arithmetic average was 558.5 (rpm), for a static stator 559.1 (rpm).
The arithmetic average value of the energy recovery during mechanical braking for a rotating stator was 5.3 J, for a static stator 2.04 J.
The number of tests and the amount of energy received for the two modes
It is worth paying attention to the nature of the polarity of the energy being recovered during mechanical braking, the voltage in the electric motor reversed its polarity:
And in a design with a static stator, the voltage did not change its polarity:
The figures shaded area of mechanical braking. One cell on the waveform for t (time) is 200 ms, for U (voltage) is 0.2 V.
To use the energy of reverse polarity, you can use a polarity switch for this purpose.
It is also worth noting that recovery with a rotating stator in the mode without mechanical braking will be less, so the "turn on" rotation of the stator before mechanical braking should be as minimal as possible, but sufficient for the rotational energy from the rotor to transfer to the stator. Judging from the oscillograms, a time of about 100 ms was sufficient, and in this period of time no significant losses are visible, it is likely that the time to a mechanical brake can still be reduced. There were ideas to make a second static stator over the rotating stator, in order to reduce losses during non-mechanical braking, but this would complicate the design of the electric motor.
Prior to this development, there was a design with a series-excited electric motor, in which the stator also rotated, with mechanical braking of the shaft.
Conclusion: In the experimental design of the engine with mechanical braking of the shaft with a rotating stator, the energy of recovery is 2.5 times greater than with a static stator, which clearly illustrates the possibility to increase the energy saving of electric motors in mechanical braking modes. The amount of energy recovery here will be more than the torque of rotation of the shaft before braking and the smaller the friction torque of the rotating stator, as well as its moment of inertia allowed for the stator to rotate, and the smaller the torque of the shaft and more of the rotating stator friction, etc. the energy of recovery will be less, i.e. in spite of the effect obtained, it is worth asking about the payback and reliability of design changes for a device in which an electric motor can be used with such an effect.
Project management: Julian Baryshnikov (designing, assembling, conducting an experiment, making parts, writing an article, an idea) - iulianbaryshnikov@yandex.ru
Project assistance: Vitaly Azarov (design, assembly, experiment), Anton Alyoshkin (design, assembly, parts manufacturing), M.V. Yakovitskaya (edited by the article), Alexander Troitsky (conducting an experiment), Nikolai Eremin (software for measuring instrument), Alena Chumak (design), FabLab Polytech SPb (manufacturing of parts, measuring instrument, conducting an experiment).
Source: https://habr.com/ru/post/225415/
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