Description:FORM – 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
Title of the invention:
AN ELECTRICALLY EXCITED SYNCHRONOUS MOTOR
Applicants:
CELECTRIC AUTOMOTIVE DRIVES PRIVATE LIMITED
An Indian Entity having address as:
VI/433, PV Building, Kollamkudimugal Road, Thrikkakara, Kerala, Cochin-682021
AND
NATIONAL INSTITUTE OF TECHNOLOGY CALICUT
An Indian Entity having address as:
NIT Campus (P.O), Calicut, Kozhikode – 673601, Kerala, India.
The following specification particularly describes the invention and the manner in which it is to be performed.
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY
The present application claims no priority from any of the patent application(s).
FIELD OF THE INVENTION
The present invention relates to an Electrically Excited Synchronous Motor. More particularly, the present invention relates to controlling of the Electrically Excited Synchronous Motor.
BACKGROUND OF THE INVENTION
Electric vehicles require efficient electric motors which gives high speed and high torque whenever required. In the prior art, motors with brushes and slip rings were used however, brushes and slip rings are prone to wear and tear, thus reducing the life of the motor. To solve this problem, Electrically Excited Synchronous Motors (EESM) are used.
Now, particularly for operations where high current is required, number of conductors or the diameter of the conductor is increased. However, passing of high current increases the temperature of the motor. To solve this problem in the prior art, heat sinks or forced cooling methods are used. However, use of heat sinks or forced cooling methods increases the size and weight of motor.
Another problem in the prior art was the use of permanent magnets. Permanent magnets are made using rare earth materials. The rare earth materials are costly which further leads to increase in the cost of manufacturing of motors.
Further, in ideal operation of the motor it is desired that the motor generates uniform torque for wide range of speeds. However, due to design constraints, it is difficult to maintain the torque high for higher levels of speed.
In light of the above stated discussion, there exists a need for improved, simple and compact design of the EESM motor which can eliminate at least one of the above stated disadvantages.
SUMMARY OF THE INVENTION
This summary is provided to introduce concepts related to an Electrically Excited Synchronous Motor. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
In an example aspect, an Electrically Excited Synchronous Motor (EESM) circuit includes an Electrically Excited Synchronous Motor (EESM). Further, the EESM is supplied with a 3-phase AC supply. A rotor includes one or more rotor conductors. A stator; and a rotary transformer. Furthermore, the rotary transformer is configured to excite the rotor. The rotary transformer includes a primary winding which is stationary and further a secondary winding which rotates along with a hollow shaft. Further, the secondary winding of the rotary transformer is connected to the rotor through a rectifier.
In an example embodiment, the EESM is connected to a single-phase inverter, further the single-phase inverter includes four switches and two legs. Furthermore, the single-phase inverter is connected to the primary winding of the rotary transformer. Induced EMF in the secondary winding is rectified via the rectifier and the rectified voltage is fed to the rotor conductors for generating flux, further flux and torque of the EESM are decoupled enabling simple speed and torque control. Efficiency of the EESM is at maximum for a wide range of operating conditions by controlling the flux, further power factor is maintained at unity in a wide range of operating conditions.
In another example embodiment, the rotary transformer includes a transformer rotor and a transformer stator. Further, the transformer rotor includes the secondary winding. Further, the transformer rotor is assembled on the hollow shaft which passes through a through bore. Furthermore, the transformer stator includes a primary winding. The primary winding is stationary, and the secondary winding rotates along with the hollow shaft. The rotary transformer is supplied with DC current and provides initial torque to start the EESM. Further, an air gap is maintained between the primary winding and the secondary winding, to generate sufficient flux and allow rotation of the rotary transformer. As rotation of the secondary winding starts magnetic path lines are generated which further generate initial torque for the rotation of the rotor.
In yet another example embodiment, the EESM may be a brushless motor and is configured to operate in low voltage (48V) (+/- 10%), high current (25A) (+/- 10%,), 1.2kW, 8 pole, 200Hz, 3000 rpm, further speed can be increased beyond 3000 rpm by flux weakening which results into at least 20% increase in the speed.
In yet another example embodiment, the stator is designed in a star configuration with about 9 turns per phase. Further, the stator enables about 3mWb flux per pole and slot pitch is about 10 mm. Further, optimum and uniform value of flux per pole reduces yoke size of the rotor thereby reducing the overall weight. Further optimum teeth size of the stator is selected to avoid saturation and ensure high mechanical stability, further depth of stator core of the stator (104) is about 120 mm (+/-0.5mm).
In yet another example embodiment, an air gap is maintained between stator and rotor, further the air gap has a flux density of about 2Wb/m2, when motor operates at the rated flux.
In yet another example embodiment, the hollow shaft is configured to accommodate a filter and the rectifier and taking wires out to rotary transformer. Further the rectifier may be an uncontrolled rectifier or a diode rectifier.
In yet another example embodiment, slot size of the rotor (102) is optimized to accommodate more than one rotor conductors, thereby increasing the number of parallel paths. Further the EESM enables 120% speed than the rated speed with 20% decrease in the rated torque by flux weakening, further high torque for short period of time is achieved by increasing a rotor current value for 3 milli second.
BRIEF DESCRIPTION OF DRAWINGS
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Figure 1 illustrates an Electrically Excited Synchronous Motor (EESM) circuit (1000), in accordance with various embodiment of the present subject matter;
Figure 2 illustrates a sectional view (2000) of an EESM (100), in accordance with various embodiments of the present subject matter;
Figure 3A-3D illustrate various views of the EESM (100), in accordance with various embodiments of the present subject matter;
Figure 4 illustrate a rotor (102) of the EESM (100), in accordance with various embodiments of the present subject matter;
Figure 5 illustrate a stator (104) of the EESM (100), in accordance with various embodiments of the present subject matter;
Figure 6 illustrate an assembly of the rotor (102) and the stator (104) of the EESM (100), in accordance with various embodiments of the present subject matter;
Figure 7 illustrates an example embodiment of the stator (104), in accordance with various embodiments of the present subject matter; and
Figure 8 illustrates a rotary transformer (106), in accordance with various embodiments of the present subject matter.
It should be noted that the accompanying figures are intended to present illustrations of exemplary embodiments of the present disclosure. These figures are not intended to limit the scope of the present disclosure.
DETAILED DESCRIPTION
As used in the specification and claims, the singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “an article” may include a plurality of articles unless the context clearly dictates otherwise. Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements, in order to improve the understanding of the present invention. There may be additional components described in the foregoing application that are not depicted in one of the described drawings. In the event such a component is described, but not depicted in a drawing, the absence of such a drawing should not be considered as an omission of such design from the specification.
In the accompanying drawings components have been represented, showing only specific details that are pertinent for an understanding of the present invention so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art having the benefit of the description herein.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.
The present subject matter relates to an Electrically Excited Synchronous Motor (EESM) (100).
Referring to figure 1 which illustrates an EESM circuit (1000). The EESM circuit (1000) includes an EESM (100). Further, the EESM (100) includes a rotor (102). The rotor (102) may include one or more rotor conductors. Further, the EESM (100) includes a stator (104). Furthermore, the EESM (100) may include a rotary transformer (106) configured to excite the rotor (102). The rotary transformer (106) includes a primary winding (106-a) and a secondary winding (106-b). The primary winding (106-a) is stationary, and the secondary winding (106-b) is configured to rotate along with a hollow shaft (202). Further, the secondary winding (106-b) is connected to the rotor (102) through a rectifier (110).
In an example embodiment, the stator (104) is designed in a star configuration with about 9 turns per phase. In addition, the stator (104) enables about 3mWb flux per pole. In an example, slot pitch is about 10 mm. In another example, the slot pitch may vary. Furthermore, optimum and uniform value of flux per pole reduces yoke size of the rotor thereby reducing the overall weight.
In another example embodiment, the EESM (100) is connected to a single-phase inverter (112). In an example, the single-phase inverter (112) may include four switches, four (body) diodes antiparallel to the switches connected in the form of a H-Bridge. In another example, the single-phase inverter (112) may include at least one switch and at least one leg. Further, the single-phase inverter (112) is connected to the primary winding (106-a) of the rotary transformer (106). Furthermore, induced electro motive force (EMF) in the secondary winding (106-b) is rectified via the rectifier (110) and the rectified voltage is fed to the rotor conductors for generating flux.
In yet another example embodiment, the secondary winding (106-b) of the rotary transformer is supplied with a DC supply. This DC supply may help in giving initial torque required for the EESM (100) to start. Once the rotor (102) starts rotating the DC supply may be cut-off.
In an example aspect, flux and torque of the EESM (100) are decoupled which enables simple control over speed and torque. Thus, flux can be controlled without affecting the torque. Also, efficiency of the EESM (100) is at maximum for wide range of operating conditions by controlling the flux and the power factor is close to unity.
In another example aspect, the EESM (100) is a brushless motor and is configured to operate in low voltage (48V) (+/- 10%), high current (25A) (+/- 10%), 1.2kW, 8 pole, 200Hz, 3000 rpm. Further, speed can be increased beyond 3000 rpm by flux weakening which results into at least 20% increase in the speed.
In yet another example aspect, the EESM (100) can achieve 120% speed than the rated speed with 20% decrease in the rated torque by flux weakening. Also, high torque for short period of time can be achieved by increasing a rotor current value for 3 milli second.
Referring to figure 2 which illustrates a sectional view (2000) of the EESM (100). The sectional view (2000) discloses the hollow shaft (202). The hollow shaft (202) may be configured to accommodate a filter and the rectifier (110) and taking wires out to rotary transformer (106). In an example, the rectifier (110) may be an uncontrolled rectifier or a single-phase diode bridge rectifier.
Referring to figure 3-A to 3-D, various views of the EESM (100) are disclosed. Figure 3-A discloses a front view of the EESM (100). Further, fig, 3-B discloses a side view of the EESM (100). Furthermore, figure 3-C discloses a rear view of the EESM (100). In addition, figure 3-D discloses an isometric view of the EESM (100).
Referring to figure 4, the rotor (102) of the EESM (100) is disclosed. The rotor (102) includes a plurality of poles (102-a). To optimize the operation of the EESM, slot size of the rotor (102) is optimized to accommodate at least two rotor conductor. In an example, slot size of the rotor (102) is optimized to accommodate three rotor conductors. This optimization of the slot size of the rotor (102) and allowing at least two rotor conductor increases the number of parallel paths. Further, increase in number of parallel paths allows flow of high amount of current through the rotor (102). In an example, this high current allows operation of high torque.
Referring to figure 5, the stator (104) of the EESM (100) is disclosed. The stator includes teeth (104-a). Further, optimum teeth size is selected to avoid saturation and ensure high mechanical stability. In an example, depth of stator core of the stator (104) is about 120 mm (+/-0.5mm).
In an example embodiment, tolerance in difference of diameter of the rotor (102) and the stator (104) is about +/- 0.5mm, to accommodate a power factor variation of about 40%, which may help to avoid saturation.
Referring to figure 6, an assembly (600) of the rotor (102) and the stator (104) is disclosed. In the assembly (600), an air gap (601) is maintained between the stator (104) and the rotor (102). The air gap (601) has a flux density of about 2Wb/m2 when motor operates at the rated flux.
Referring to figure 7, an example embodiment of the stator (104) with different poles is shown. The poles such as (A, -A), (B, -B), (C, -C) can be seen on the stator (104). Further, stator (104) may include 24 such poles.
Referring to figure 8, a rotary transformer (106) is disclosed. The rotary transformer (106) includes a transformer rotor (106-d), a transformer stator (106-e). Further, the transformer rotor (106-d) includes a secondary winding (106-b). Furthermore, the transformer rotor (106-d) is assembled on the hollow shaft (202) which passes through a through bore (106-g). Moreover, the transformer stator (106-e) may include a primary winding (106-a). The primary winding (106-a) is stationary, and the secondary winding (106-b) may rotate along the hollow shaft (202). The rotary transformer (106) is supplied with DC current and provides initial torque to start the EESM (100). Further, an air gap (106-c) is maintained between the primary winding (106-a) and the secondary winding (106-b), to generate sufficient flux and allow rotation of the rotary transformer (106-d). As rotation of the secondary winding (106-b) starts magnetic path lines (106-f) are generated which further generate initial torque for the rotation of the hollow shaft (202).
Technical Advancement & Economic Significance:
The benefits of the Electrically Excited Synchronous Motor may include but are not limited to:
The EESM enables 120% speed than the rated speed with 20% decrease in the rated torque by flux weakening.
High torque for a short period of time is achieved by increasing the rotor current value by 3 milli seconds.
Use of the rotary transformer may avoid use of brushes. Thus, life expectancy of the EESM may increase.
Using flux weakening technique along with the modified design of the rotor may increases the number of parallel paths which allows high torque and high speed operation for wider range of speed.
Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as “including,” “comprising,” “incorporating,” “consisting of,” “have,” “is,” “include” used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.
, Claims:WE CLAIM:
1. An Electrically Excited Synchronous Motor (EESM) circuit (1000) comprising:
an EESM (100);
a rotor (102), wherein the rotor (102) comprises one or more rotor conductors;
a stator (104), wherein the EESM (100) is supplied with a 3-phase AC supply (108) to the stator (104); and
a rotary transformer (106), wherein the rotary transformer (106) is configured to excite the rotor (102), wherein the rotary transformer (106) comprises a primary winding (106-a) and a secondary winding (106-b), wherein the primary winding (106-a) is stationary and the secondary winding (106-b) rotates along with a hollow shaft (202), wherein the secondary winding (106-b) is connected to the rotor (102) through a rectifier (110),
wherein the EESM (100) is connected to a single-phase inverter (112), wherein the single-phase inverter (112) is connected to the primary winding (106-a) of the rotary transformer (106), wherein induced EMF in the secondary winding (106-b) is rectified via the rectifier (110) and rectified voltage is fed to the rotor conductors for generating flux, wherein flux and torque of the EESM (100) are decoupled which enables simple control of speed and torque.
2. The EESM circuit (1000) as claimed in claim 1, wherein efficiency of the EESM (100) is at maximum for a wide range of operating conditions by controlling the flux, wherein power factor is maintained at unity in a wide range of operating conditions.
3. The EESM circuit (1000) as claimed in claim 1, wherein the rotary transformer (106) comprises a transformer rotor (106-d) and a transformer stator (106-e), wherein the transformer rotor (106-d) comprises a secondary winding (106-b) and the transformer rotor (106-d) is assembled on the hollow shaft (202) which passes through a through bore (106-g), wherein the rotary transformer (106) is supplied with DC current and provides initial torque to start the EESM (100), wherein an air gap (106-c) is maintained between the primary winding (106-a) and the secondary winding (106-b), to generate sufficient flux and allow rotation of the transformer rotor (106-d), further, as rotation of the secondary winding (106-b) starts, magnetic path lines (106-f) are generated which further generate initial torque for the rotation of the rotor (102).
4. The EESM circuit (1000) as claimed in claim 1, wherein the EESM (100) is a brushless motor and is configured to operate in low voltage (48V) (+/- 10%), high current (25A) (+/- 10%), 1.2kW, 8 pole, 200Hz, 3000 rpm, wherein speed can be increased beyond 3000 rpm by flux weakening which results into at least 20% increase in the speed.
5. The EESM circuit (1000) as claimed in claim 1, wherein the single-phase inverter (112) comprises four switches, four (body) diodes anti parallel to the switch and two legs.
6. The EESM circuit (1000) as claimed in claim 1, wherein the stator (104) is designed in a star configuration with about 9 turns per phase, wherein the stator (104) enables about 3mWb flux per pole, wherein slot pitch is about 10 mm, wherein optimum and uniform value of flux per pole reduces yoke size of the rotor thereby reducing an overall weight.
7. The EESM circuit (1000) as claimed in claim 1, wherein an air gap is maintained between the stator (104) and the rotor (102), wherein the air gap has a flux density of about 2Wb/m2, when motor operates at rated flux.
8. The EESM circuit (1000) as claimed in claim 1, wherein the hollow shaft (202) is configured to accommodate a filter and the rectifier (110) and taking wires out to rotary transformer (106), wherein the rectifier (110) is an uncontrolled rectifier or a diode rectifier.
9. The EESM circuit (1000) as claimed in claim 1, wherein optimum teeth size is selected to avoid saturation and ensure high mechanical stability, wherein depth of stator core of the stator (104) is about 120 mm (+/-0.5mm).
10. The EESM circuit (1000) as claimed in claim 1, wherein slot size of the rotor (102) is optimized to accommodate more than one rotor conductors, thereby increasing number of parallel paths.
11. The EESM circuit (1000) as claimed in claim 1, wherein the EESM (100) enables 120% speed compared to rated speed with 20% decrease in rated torque by flux weakening, wherein short time high torque is achieved by increasing a rotor current value for 3 milli seconds.

Dated this 29th day of April 2024

Abhijeet Gidde
Agent for the Applicant
IN/PA-4407