EP3539199A1

EP3539199A1 - An electrical machine with a stator having multiple sections winding coil and switch combinations

Info

Publication number: EP3539199A1
Application number: EP17869388.3A
Authority: EP
Inventors: Dhiyanesh RADHAKRISHNAN; Venkata RAGHUNATH KUMAR RACHABATTUNI; Ujjwal GANGULY; Samraj JABEZ DHINAGAR
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2016-11-09
Filing date: 2017-11-09
Publication date: 2019-09-18
Also published as: CN110168866A; EP3539199A4; WO2018087689A1

Abstract

The present invention relates to an electrical machine for attaining varying torque at different speeds in vehicles by using switch combinations. The electrical machine comprises a coil with multiple sections C1, C2, C3, C4, C5, C6 connected such that all sections are in a series configuration to increase the Kt and some of the sections C1, C2, C3, C4, C5, C6 are connected in parallel to reduce the K_e. This increases the no-load speed during the motoring mode and reduces the voltage generated by the machine during the generation mode, by using switch arrangements. When the sections C1, C2, C3, C4, C5, C6 are connected in parallel, it reduces the resistance of each phase thereby reducing the copper losses and thus improves the efficiency of the machine. The applications are in integrated starter generator (ISG) system of any vehicles to provide high starting torque and to generate less voltage at high rpm. Also, can be used in any motor to provide torque to the vehicle at higher speeds.

Description

AN ELECTRICAL MACHINE WITH A STATOR HAVING MULTIPLE SECTIONS WINDING COIL AND SWITCH COMBINATIONS

FIELD OF THE INVENTION

[0001] The present invention relates to an electrical machine for vehicles. More particularly, the present invention relates to a stator winding coil of the electrical machine for attaining varying torque at different speeds in vehicles.

BACKGROUND

[0002] In automotive vehicles, the starter motor is used to start the engine when the vehicle is at rest. The starter motor provides very high torque to crank the engine at the starting (low-speed operation). The vehicle also has a magneto which generates power (high-speed operation) to the vehicle electrical loads and also to the battery.

[0003] When the function of the starter motor and magneto is combined into one single machine that has conflicting requirements, (i.e.) high starting torque and generate less voltage at high rpm, lest the cost of the controller increases to with stand these high voltages generated. The starting torque requires a high K_t. The K_t is a design constant of the machine, which is used to represent the produced torque based on the input current as per the following equation.

T = K_t*I

To generate less voltage at high rpm, a less Ke is required. Ke is the backemf constant of the machine which is used to represent the backemf voltage induced in the coils at a given speed com.

E_b = K_b*co_m

[0004] However, the machine usually has identical values for Kt and Ke, by which the starting torque and the no-load rpm of the machine are fixed. There are various methods to change the Kt and Ke constants like, field weakening, moving the rotor to provide less flux path, double stator configurations, etc. [0005] EP1255345 Al titled D High performance stator deviceD discloses about changing the number of turns by having multiple coils individually chosen or connected in "series." At any point in time, the coils are either connected individually or in series to change the Kt value of the machine.

[0006] The coils are never connected in parallel. Parallel configuration allows the machine to operate at an increased efficiency zone by reducing the losses. In the present invention, a single coil is tapped to create the effect of different turns of the windings. The coil ends are not separated, as opposed to EP1255345(A1).

[0007] US2016-0141996A discloses an electric motor system for the vehicles that adjusts a coil winding number of a vehicle electric motor. The electric motor system comprises an inverter that includes a power switching circuit attached in parallel to a vehicle battery and a coil switching circuit, where the coil switching circuit receives and sends a driving current with different phases generated according to a switching operation of the power switching circuit, connected to the power switching circuit; an electric motor configured to comprise more than one winding coil that accepts the driving current wounded at multi stages; and a controller configured to check a switching operation of the coil switching circuit that adjusts a winding number to a maximum coil winding number of more than one winding coils by connecting all the winding coils serially in a low-speed driving mode and to a minimum coil winding number by connecting some of the winding coils serially in a high-speed driving mode. In this patent, the coils are connected in series to reduce the K_e to change the speed in the driving mode.

[0008] US 20140265693A1 titled D Integrated starter generatorD discloses D an integrated starter generator (ISG) system comprising a flux-regulated permanent magnet machine (PMM), a wound-field synchronous machine, and a control coil controller. There is a control coil in a stationary portion and more than one permanent magnet rotating armature windings in a rotating portion in the flux-regulated PMM. [0009] The wound field synchronous machine includes a stationary portion and a rotating portion. The stationary portion comprises the main armature winding whereas the rotating portion comprises a main field winding that receives excitation from the flux regulated PMM. The control coil controller controls the current supplied to the flux regulated PMMDs control coil to selectively limit the magnetic flux given to the rotating armature windingsD . (sic US Publication No. 20140265693 Al).

[00010] WO2013/054349 A2 titled D Torque assist for motors discloses D a method to provide a selective torque assists to the primary motor in an electric vehicle/Hybrid vehicle. The method comprises of embedding torque assists motors on the two output shafts of the primary motor differential. The torque assists motors can be turned ON to provide a short term torque boost to the primary motor differential at zero or a very low-speed. The torque assists motors can have multiple windings to provide different torque boost. D (Sic. Publication No. WO2013/054349 A2)

SUMMARY OF THE INVENTION

[00011] A coil with multiple sections is connected such that all sections are in a series configuration to increase the Kt at one instance and at another instance, some of the sections are connected in parallel to reduce the Ke (and hence Kt). This increases the no-load speed during the motoring mode and reduces the voltage generated by the machine during the generation mode, by using switch arrangements. When the sections are connected in parallel, it reduces the resistance of each phase thereby reducing the copper losses. This improves the efficiency of the machine.

[00012] The arrangement of switches is such that the tapped portion does not disconnect the coil sections. But instead, the voltage is applied across the tapped portion between the sections and one of the power supply pin. The use of tapped portions to apply the voltages reduces the number of wires from the machine to connect to the switch system. [00013] In another embodiment, coils on different teeth are also connected in series and parallel combination using the switches to change the K_t (and K_e) of the machine. The connection allows the machine to be taken to the next nearest possible motoring speed range and to operate at the corresponding speed band in the highest efficiency zone. When the coils on different teeth are connected in parallel, the effective number of turns is reduced in the phase winding, thereby reducing the K_t and K_e of the machine. The switches are energized such that the parallel path count is increased in successive steps to reduce the K_e of the machine in steps. This allows the machine to operate efficiently in the next motoring speed range. The motoring speed range is the range of the speed values from zero rpm to the maximum no-load rpm of the machine for a given input conditions.

[00014] The present invention can be utilized in any vehicle and can be applied to any (Integrated starter generator) ISG system to provide a high starting torque and to generate less voltage at high rpm. By reducing the K_e of the machine, the traction motors speed range can be improved thereby providing a wider speed range within the same geometry, and provide better regeneration capabilities. The application can also be extended for any motor to provide the torque to the vehicle at higher speeds.

BRIEF DESCRIPTION OF THE DRAWINGS [00015] Figure 1 illustrates the teeth with three sections of coils and two switches of single throw double pole type.

[00016] Figure 2 illustrates the teeth with three sections of coils and two switches of single pole single throw type.

[00017] Figure 3 illustrates the teeth with five sections of coils and four switches of single throw multiple pole type.

[00018] Figure 4 illustrates the teeth with five sections of coils and four switches of single pole single throw type.

[00019] Figure 5 illustrates the teeth with five sections of coils and six switches of single pole single throw type. [00020] Figure 6 illustrates the teeth with five sections of coils and six switches, five switches are of single pole single throw type, and one switch is of double pole single throw type.

[00021] Figure 7a illustrates the teeth with five sections of coils and six switches all of which are single pole single throw type switches.

[00022] Figure 7b illustrates the teeth with five sections of coils and six switches, in which four switches are of single pole single throw and two switches are of double pole single throw types.

[00023] Figure 8 illustrates the teeth with five sections of coils and eight switches which can be either of single pole single throw type or multi pole single throw type.

[00024] Figure 9 illustrates the teeth with two sections of coils and three single pole single throw switches.

[00025] Figure 10 illustrates the teeth with four sections of coils, and six switches can be either of single pole single throw or of multiple pole single throw types.

[00026] Figure 11 illustrates the teeth with six sections of coils and eight switches.

[00027] Figure 12 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 8.

[00028] Figure 13 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 9.

[00029] Figure 14 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 9.

[00030] Figure 15 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 8.

[00031] Figure 16 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 10. [00032] Figure 17 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figure 10.

[00033] Figure 18 illustrates the torque and efficiency of the machine with respect to speed for the coils section connected as in Figures 8 and 10. DETAILED DESCRIPTION

[00034] The Integrated Starter Generator (ISG) or traction motor needs a high starting torque at the beginning. To produce this starting torque, the machine is initially designed with higher K_t. To design a machine with higher K_t, more number of turns in each phase is needed. Instead of having all the turns as a coil with a single section, having a coil with multiple sections is proposed. These coils with multiple sections are wound on the same tooth of the stator. The start and end wires of each section of the coils are then taken out and are connected by switches. During the start, each section of the coils is connected in such a way that the end of the first section of the coils 3, 5 and the start of the next section of the coils 2, 4 are connected, as in Figure 1. The start 6 of the first section of coil CI is connected to the phase terminal of the controller 50, and the end wire of the last section 1 of the coil C3 is connected to either to another phase terminal of the controller or can be a neutral point of the machine winding 60. Then, each phase has more number of turns that are connected in series configuration with respect to each other. Subsequently, to increase the speed range of the motoring mode to the next possible limit, the switch configurations are so energised that there are some sections of the coils which are connected in parallel and some sections of the coils are in series, based on the sections and the turns in the entire section of coils.

[00035] The machine is allowed to operate at that motoring speed range so that the resistance is reduced and it can be conveniently operated in the highest efficiency of that band. Further, the next possible motoring speed band is achieved by the switching arrangements by reducing the turns and by increasing the sections of the coils in parallel, thereby ensuring that the machine is operated near the maximum efficiency range by all possible switch combinations. [00036] In an odd number of sections of coils, for example, three sections as in Figure 1, at normal operation, switches slOl and sl02 are open and all the coil sections CI, C2, C3, are connected in series configuration. The higher turns in series configuration give a higher K_t. The switches slOl and sl02 are single throw double pole switches. In generation mode, the switches slOl and sl02 are closed. The coils sections CI, C2, C3 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The three coils sections CI, C2, C3, are connected in parallel, reducing the turns, thereby increasing the no-load speed and hence the motoring speed range of the motor. The peak of efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency.

[00037] For odd number of sections of coils, say three as shown in Figure 2, in normal operation, switches s201 and s202 are open and all the coil sections CI, C2, C3 are connected in a series configuration. The higher turns in series configuration give a higher K_t, which increases the torque 500 of the machine. The switch s201 and s202 are single pole single throw switches. In generation mode, the switches s201 and s202 are closed. The coils sections CI, C2, C3, are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The three coils sections CI, C2, C3, are connected in parallel, reduces the turns, thereby increasing the no-load speed and hence the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs operating efficiency. When either of s201 or s202 is closed, there will be only one coil section that will be connected. There will be a lesser number of turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve of the motor is also shifted to the right side of the image, improving the systemDs efficiency For odd number of sections of coils, say five as shown in Figure 3, in normal operating condition, switches s301, s302, s303, s304 are open, all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s301, s302, s303, and s304 are single throw multi pole switches. In generation mode, the switches s301, s302 s303 and s304 are closed. The coils sections are connected in parallel, reducing the resistance of the machine, thereby improving the efficiency 600 of the machine. The five coils sections CI, C2, C3, C4, and C5 are connected in parallel, which reduces the number of turns in each phase, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency. For the same odd section of coils as shown in Figure 4, in normal operation, the switches s401, s402, s403 and s404 are open. All the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s401, s402 s403, and s404 are single pole single throw switches. In generation mode, the switches s401, s402, s403, and s404 are closed. The coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The five coils sections CI, C2, C3, C4, and C5 are connected in parallel, which reduces the number of turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image improving the systemDs efficiency.

[00038] In the same section of coils, if it is connected as in Figure 5, in normal operation, switch s503 is closed and switches s501, s502, s504, s505 are open, and all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s501, s502, s503, s504, s505, and s506 are single pole single throw switches. When the switches s506 and s505 are closed and all other switches are open, there are two coil sections. C5 is in series with C4, C3, is in series with C2, these two coil sections C4-C5 and C3-C2 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches s501, s502, s503, s504, and s505 are closed. The coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The five coils sections CI, C2, C3, C4, and C5 are connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency.

[00039] The same section of coils if connected as in Figure 6, in normal operation, switch s603 is closed and switches s601, s602, s604, and s605 are open, all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t. The switches s602, s603, s604, and s605 are single pole single throw switches. s606 is a double pole single throw switch. s601 can be either a single pole single throw switch or a double pole single throw switch. . When switches s606 and s605 are closed and all other switches are open, there are two coil sections, C4 is in series with C5 and C3 is in series with C2 are in series connection, two coil sections C4-C5 and C3-C2 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches s601, s602, s603, s604, and s605 are closed. The coils sections CI, C2, C3, C4, and C5 are now connected in parallel, the resistance of the machine is reduced, the number of turns in each phase is reduced, thereby increasing the no-load speed and the motoring speed range of the motor, and it also improves the peak of the efficiency 600 of the machine. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the system efficiency.

[00040] When the section of coils are connected as in Figure 7a, in normal operation, switch s703 is closed and switches s701, s702, s704, s705, and s706 are open, all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s701, s702, s703, s704, s705, and s706 are single pole single throw switches. When switch s701 and s706 are closed and all other switches are open, there are two coils sections CI is in series with C2 and C3 is in series with C4, two coil sections C3, C4 and CI, C2 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches s701, s702, s703, s704 and s705 are closed. The coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The five coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency.

[00041] When the section of coils are connected as in Figure 7b, in normal operation, switch s703 is closed and switches s701, s702, s707, s705, and s708 are open, all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s701, s702, s703, s707, and s705 are single pole single throw switches. The switches s703 and s708 is a double pole single throw switch. When the switches s701 and s708 are closed and all other switches are open, there are two coil sections CI, C2 and C3, C4 are in series connection, two coil sections C1-C2 and C3-C4 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches s701, s702, s703, s707, and s705 are closed. The coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The five coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency.

[00042] When the section of coils are connected as in Figure 8, in normal operation, switches s803 and s804 are closed and the switches s801, s802, s805, s806, s807 and s808 are open, and all the coil sections CI, C2, C3, C4, and C5 are connected in series configuration. The higher turns in series configuration gives a higher K_t which increases the torque 500 of the machine. The switches s801, s802, s803, s804, s805, s806, s807, and s808 are single pole single throw switches. The switches s801, s802, s804, s805, s807, and s808 can also be multi pole single throw switches. When the switches s801, s803, and s808 are closed and all other switches are open, there are two coil sections C4 is in series with C3 and C2 is in series with CI are in series connection, two coil sections C4-C3 and C2-C1 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. When the switches s804, s806, and s807 are closed and all other switches are open, there are two coil sections C2 in series with C3 and C4 is in series with C5, two coil sections C2, C3 and C4, C5 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches s801, s802, s803, s804, s805 and s806 are closed. The coils sections are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency 600 of the machine. The five coils sections CI, C2, C3, C4, and C5 are now connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency, as shown in Figures 12, 15 and 18.

[00043] In even sections of coils say for two when it is connected as shown in Figure 9, in normal operation, the switch s903 is closed and switches s901 and s902 are open, all the coil sections CI and C2 are connected in series configuration. The higher turns in series configuration gives a higher K_t, which increases the torque 500 of the machine. The switches s901, s902 and s903 are single pole single throw switches. In generation mode, the switches s901 and s902 are closed. The coils sections CI and C2 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The two coils sections CI and C2 are now connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve 600 of the motor is also shifted to the right side of the image, improving the systemDs efficiency (as shown in Figures 14 and 13). In the same even sections of coils say for four when it is connected as shown in Figure 10, in normal operation, the switch sl006 is closed and the switches slOOl, sl002, sl003, sl004, and sl005 are open, all the coil sections CI, C2, C3, and C4 are connected in series configuration. The higher turns in series configuration gives a higher K_t which increases the torque 500 of the machine. The switch slOOl, sl002, sl003, sl004, sl005 and sl006 are single pole single throw switches. The switches slOOl, sl002, sl004, and sl005 can also be multi pole single throw switches. When switches sl003 and sl005 are closed and all other switches are open, there are two coil sections CI, C2 and C3, C4 are in series connection, two coil sections CI, C2 and C3, C4 are in parallel to the circuit. The turns are reduced, reducing the K_e of the machine. In generation mode, the switches slOOl, sl002, sl004, and sl005 are closed. The coils sections CI, C2, C3, and C4 are now connected in parallel, reducing the resistance of the machine, thereby improving the efficiency of the machine. The four coils sections CI, C2, C3, and C4 are now connected in parallel, reducing the turns, thereby increasing the no-load speed and the motoring speed range of the motor. The peak of the efficiency curve of the motor is also shifted to the right side of the image, improving the systemDs efficiency as shown in Figures 16-18.

[00044] The same configuration can also be extended to coils on different teeth which can also be connected in series or parallel combination. For example, a stator having 6 teeth per phase as shown in Figure 11, when all the coils CI, C2, C3, C4, C5 and C6 in the teeth are connected in series, the machine has a higher K_t which increases the torque 500 of the machine and K_e values. In this configuration, the end coils of the first phase and the start coils of the next phase are connected in series by closing the switch sllOl to achieve the series configuration. When there is a requirement to reduce the K_e of the machine as in the switches sll02, sll03 are connected to the circuit and the switch sllOl is disconnected. Then there is effectively two parallel paths for each phase. This arrangement switches the machine from single parallel path to two parallel paths. The same can be extended to three parallel paths by closing switches sllOl, sll05, sll06, sll07 and sll08 and opening the switches sll04, sll02, sll03 and sll09. The advantage of switching between the parallel paths is to increase the motoring speed range of the machine thereby allowing the machine to operate on or near the highest efficiency operating zone.

[00045] All the switches can either be operated independently or can be operated at the same time to create different values of K» (or K_t). The sections of coils can be either in series or parallel and so are the coils on different teeth at the same time to reduce the K» values.

[00046] Advantageously, present invention aims at achieving different K_e (or K_t) values at different speeds by switch combinations for the stator winding.

[00047] Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

Claims

We claim:

1. An electrical machine comprising:

a stator winding coil with multiple sections; switches; and voltage terminals;

said stator ending coil utilizes switch combinations to connect the sections in series and parallel for varying torque constant (K_t) and back-emf constant (K_e); said coil with multiple sections CI, C2, C3, C4, C5, C6 is wound on the same tooth of the stator;

start and end wires of each section of coils are taken out and connected through the switches;

each section of the coils is connected, such that end of first section of the coils (3), (5) and start of next section of the coils (2), (4) are connected, during the start; and start (6) of the first section of coil CI is connected to the phase terminal of a controller (50) and end wire of last section (1) of a coil C3 is connected either to another phase terminal of the controller (50) or the neutral point of the machine winding (60), so that each phase has more number of turns that are connected in series.

2. The electrical machine as claimed in claim 1, wherein the switches are single pole single throw switch, multiple pole single throw switch and double pole single throw switch.

3. The electrical machine as claimed in claim 1, wherein to increase speed range in motoring mode to a next lowest possible limit, switch configurations are energised in order to have parallel connections for some sections and series connections for some sections of the coils, based on the sections and turns in the entire section of coils.

4. The electrical machine as claimed in claim 1 , wherein the coil with multiple sections is connected, such that,

all sections are in series configuration to increase the K_t and at different point of time some of the sections are connected in parallel to reduce the ¾;

no-load speed increases during motoring mode and reduces the voltage generated by the machine during the generation mode, by using switch arrangements; and when the sections are connected in parallel, reduce the resistance of each phase, thereby minimizing the copper losses.

5. The electrical machine as claimed in claim 1, wherein arrangement of switches enables voltage applied across tapped portion between the sections and one of power supply pin, rather disconnecting coil sections and use of tapped portions to apply the voltage reduces number of wires from the machine to connect to switch system.

6. The electrical machine as claimed in claim 1, wherein coils on different teeth are also connected in series and parallel combination using the switches to change the K_t and K_e values of the machine.

7. The electrical machine as claimed in claim 6, wherein the connection allows the machine to be taken to the next nearest possible operating speed range and to operate at the corresponding speed band in a highest efficiency zone.

8. The electrical machine as claimed in claim 6, wherein parallel connection of coils on different teeth reduces the effective number of turns in phase winding, thus lowers the K_t and K_e of the machine.

9. The electrical machine as claimed in claim 6, wherein the switches are energized leading to increase in parallel path count in successive steps to reduce the K_e of the machine in steps, thus allows efficient operation in the next operating range.

10. The electrical machine as claimed in claim 1 , wherein the higher turns in series configuration gives a higher Kt, which increases the torque (500) of the machine.

11. The electrical machine as claimed in claim 1, wherein the switches are operated independently to create different values of Ke (or Kt).

12. The electrical machine as claimed in claim 1 , wherein the switches are operated independently at the same time to create different values of Ke (or Kt).