NL2020150B1 - A Switched Reluctance Motor, SRM, system with short flux path. - Google Patents

Abstract

A Switched Reluctance Motor, SRM, system having integrated power stages, said electric motor system comprising a rotor, a stator, a plurality of power stages, and a cooling system comprising a substantially flat hollow main cool body arranged to support the flowing of a cooling medium inside said hollow main cool body for cooling said main cool body, a base cooling plate connected to a first flat surface of said hollow main cool body and to said plurality of power stages for transferring heat between said plurality of power stages and said base cool plate, heat resistance inserts connected to said base cooling plate and said plurality of electrically excitable coils for transferring heat between said plurality of coils and said base cooling plate wherein said heat resistance inserts provide for a thermal conductivity, thereby creating a thermal buffer such that said electrically excitable coils are cooled less compared to said power stages, by said cooling system.

Description

Title: A Switched Reluctance Motor, SRM, system with short flux path.

Description

The present invention is related to Switched Reluctance Motor, SRM, systems with short flux path, more specifically to Switched Reluctance Motor, SRM, systems comprising a stator having electrically excitable coils, and a rotor having ferromagnetic material for supporting the flow of flux, which rotor is arranged to rotate with respect to the stator.

In general, a brushless electric motor refers to a Direct Current, DC, motor wherein a mechanical brush and a commutator have been modified into electric means. Accordingly, since such a brushless electric motor does not generate abrasion, dust and electric noise, and has good output and efficiency, it is appropriate for, for example, a high-speed rotation type motor, so that various researches and developments have been conducted on the next generation motor.

However, in case of the brushless electric motor, a rotor of a DC motor, around which coils are wound, is substituted with a permanent magnet, and a method of controlling the speed is switched from a voltage control type into an excitation phase control type, so that a driving circuit, in the form of power control means, is required.

In general, a brushless electric motor comprises a rotor comprising a plurality of permanent magnets, and a stator comprising a plurality of electrically excitable coils for generating an induction field for interaction with said plurality of permanent magnets to cause said rotor to rotate with respect to said stator.

In general, a Switched Reluctance Motor, SRM, systems comprises a rotor without permanent magnets, wherein the rotor is arranged to support the flow of a flux between a pair of stator teeth.

The drawbacks of known motor systems is that they are not sufficiently reliable and safe, especially when they are to be used in fields like electric cars or the like.

It is therefore an object of the present invention to provide for a Switched Reluctance Motor, SRM, system with short flux path which is inherently more reliable and safe.

In order to achieve that object, the invention provides, in a first aspect thereof, in a Switched Reluctance Motor, SRM, system with short flux path, comprising: a rotor comprising a plurality of rotor teeth; a stator comprising at least three adjacently placed groups of at least three phases each, wherein each phase is associated with one stator tooth of said stator within a corresponding group, wherein electrically excitable coils are wound on each stator tooth, respectively, thereby providing single phase coils for generating induction fields for providing short flux paths in interaction with said rotor teeth to cause said rotor to rotate with respect to said stator, wherein each group is associated with at least three power stages, comprised by said motor system, such as h-bridges or asymmetric bridge converter, wherein each power stage is arranged to drive a single phase coil in such a way that adjacent coils of said rotor provide for oppositely directed induction fields.

One of the advantages of the architecture as provided above is that the power stages may be placed close to the electronically excitable coils. Further, the motor system is divided into at least three groups, wherein each group has at least three phases, which provides for a more reliable, redundant, system. The above accomplishes that the Switched Reluctance Motor, SRM, system is inherently more reliable, safe and redundant compared to conventional motor systems.

Another advantage of the Switched Reluctance Motor, SRM, system according to the present invention is that, due to above disclosed features, the power stages, the rotor and the stator can be construed as a single integral part.

In accordance with the present invention, a single power stage may comprise a H-bridge composed of four power Field Effect Transistors, wherein the output of a single H-bridge is directly connected one coil. A brushless electric motor is also known as an electronically commutated motor, which is a synchronous motor that is powered by a Direct Current, DC, electric source via power stages, which produce an AC electric signal to drive the coils and thus the motor. In this context, AC, alternating current, does not imply a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform. Additional sensors and electronics eventually control the outputs of the power stages in their amplitude, waveform and frequency, i.e. rotor speed.

The Switched Reluctance Motor, SRM, system comprises a rotor which does not comprise permanent magnets. In accordance with the present disclosure, the rotor is to support the flow of flux between two adjacently placed stator teeth. The flux thus does not flow from one tooth of the stator to a tooth opposite to that particular tooth. The present disclosure is directed to a short path principle in which the flux flows from one tooth of the stator via the teeth of the rotor back to the stator again, more specifically to a tooth of the stator adjacent to the initial tooth.

Based on the above, the invention comprises at least three groups of three stator teeth, wherein electrically excitable coils are wound on each of the stator teeth respectively. As such, according to the invention, the Switched Reluctance Motor, SRM, system comprises at least nine coils. As mentioned before, each coil has its own power stage such that the Switched Reluctance Motor, SRM, system also comprises at least nine power stages. There is thus a direct coupling between the amount coils and the amount of required power stages.

Further, the invention is directed to a Switched Reluctance Motor, SRM, system. In accordance with the present invention, the Switched Reluctance Motor, SRM, system may also be used as a generator for generating electrical power. The Switched Reluctance Motor, SRM, system may also be used as a combined motor and generator in one.

It is noted that, in accordance with the present disclosure, the stator comprises at least nine stator teeth, preferably at least fifteen stator teeth, and thus also at least nine, preferably at least fifteen, electrically excitable coils. These at least nine coils are divided into at least three groups. The advantage hereof is that the Switched Reluctance Motor, SRM, system is to provide power even when one of the at least three groups breaks down. As such, at least two groups will still function properly which ensures that a reduced power is still producible by the Switched Reluctance Motor, SRM, system. As such, the concept of the present disclosure is directed to redundancy to a certain extend. That is, the Switched Reluctance Motor, SRM, system is able to provide power even in situations wherein one of the groups has broken down. In an example, the stator comprises at least three adjacently placed groups of at least five phases each.

In a further example, each adjacently placed coil is wound oppositely. The result hereof is that the induction fields of adjacently placed coils are directed oppositely, when driven in a same manner.

As an alternative, each adjacently placed coil is wound in a same direction, and wherein each adjacently placed coil is oppositely driven, by said corresponding h-bridge.

In accordance with the present disclosure, an H-bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. These circuits are used in different types of fields to allow electric motors to run forwards and backwards.

As mentioned above, coils are wound on stator teeth which are positioned adjacently to each other along the circumference of the stator. In order to make sure that the induction fields generated by adjacently placed coils oppositely directed to each other, each time a power stage drives these coils, the inventor has found that it is advantageous that the winding of these coils of adjacently placed coils are different. This makes sure that, according to the well known right-hand rule, the induced magnetic fields are directed oppositely.

One of the advantages of the example as provided above is that, due to the cascading of the adjacent coils, short connections can be provided which reduces any losses, for example Ohmic losses that occur due to the current flowing through the branches of the coils. Another advantage is that effective flux paths are created on relatively high power density.

This example is advantageous as, due to the redundant implementation, it further improves the reliability of the system. Any electrically excitable coil and/or particular power stage may still break down but the remaining, i.e. properly functioning, coils and power stages will make sure that the Switched Reluctance Motor, SRM, system will still function decently. That is, the Switched Reluctance Motor, SRM, system may have reduced power due to any break down in a coil or particular power stage, but the Switched Reluctance Motor, SRM, system will still function.

In another example, the comprises at least three sub control units, wherein each sub control unit is associated with power stages of one particular group, wherein each sub control unit is arranged for actuating said corresponding power stages.

The advantage of this example is that it further improves the reliability of Switched Reluctance Motor, SRM, system. Two sub control units can make sure that the Switched Reluctance Motor, SRM, system is functioning properly in case one of the three sub control units breaks down. The Switched Reluctance Motor, SRM, system may then, however, function with a reduced power.

Here, it is preferred in case each of the sub control units comprise its own rotor position sensor for determining a position of said rotor with respect to said stator, as in such a case the sub control units do not rely on a single rotor position sensor for determining the position of the rotor with respect to the stator. In accordance with the present invention, a rotor position sensor is, for example, a hall sensor which is a transducer that varies its output voltage in response to a magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications.

In an example, Switched Reluctance Motor, SRM, system further comprises a master control unit arranged for controlling said three sub control units based on inputs in said master control unit related to any of speed, torque, accelerator and brake signals.

In another example, the said rotor surrounds said stator.

In a further example, said stator surrounds said rotor.

In another aspect, there is provided a method of operating a Switched Reluctance Motor, SRM, system according to any of the previous examples.

In a further aspect, there is provided a motorized electrical vehicle comprising a Switched Reluctance Motor, SRM, system according to any of the examples as provided above.

Another drawback of known Switched Reluctance Motor, SRM, systems is that they are not sufficiently reliable and safe, especially when they are to be used in fields like electric cars or the like.

It is therefore another objective of the present invention to provide for a Switched Reluctance Motor, SRM, system with a cooling system which is more efficient and simpler compared to the prior art.

In order to achieve that object, the present disclosure provides, in a first aspect thereof, in a Switched Reluctance Motor, SRM, system having integrated power stages, said electric motor system comprising: a rotor comprising a plurality of rotor teeth; a stator comprising a plurality of stator teeth placed adjacently to each other, wherein electrically excitable coils are wound on each of said teeth, respectively, for generating an induction field for interaction with said plurality of rotor teeth to cause said rotor to rotate with respect to said stator, a plurality of power stages, such as H-bridges, wherein each power stage is arranged to drive a coil of said coils wound on said plurality of teeth; a cooling system comprising: a substantially flat hollow main cool body arranged to support the flowing of a cooling medium inside said hollow main cool body for cooling said main cool body; a base cooling plate connected to a first flat surface of said hollow main cool body and to said plurality of power stages for transferring heat between said plurality of power stages and said base cool plate; heat resistance inserts connected to said base cooling plate and said plurality of electrically excitable coils for transferring heat between said plurality of coils and said base cooling plate, wherein said heat resistance inserts provide for a thermal conductivity, thereby creating a thermal buffer such that said electrically excitable coils are cooled less compared to said power stages, by said cooling system.

It was the insight of the inventor to provide a cooling system with a single substantially flat hollow main cool body, which is used to cool the electrically excitable coils as well as the power stages. As such, one cooling system is provided to cool both the electrically excitable coils and the power stages.

The inventor noted that, typically, the operating temperature of the electrically excitable coils is much higher compared to the operating temperature of the power stages. As such, in the prior, two cooling systems are used. One cooling system for cooling the power stages and one cooling system for cooling the electrically excitable coils.

The inventor noted that having two cooling systems is not desired as in such a case also two pumps for pumping the cooling medium, two piping systems for transporting the cooling medium, two cool bodies, two cooling plates, etc., are required. All these aspects require space which is usually of the essence in a Switched Reluctance Motor, SRM, system. By using a single cooling system, the weight of the Switched Reluctance Motor, SRM, system, and thus also its efficiency, is further improved.

One of the aspects of the disclosure is that heat resistance inserts are provided between the electrically excitable coils and the base cool plate for amending the thermal conductivity between the coils and the base plate. The advantage hereof is that the electrically excitable coils, having a different desired operating temperature, can be cooled from the same main cool body as compared to the power stages. As such, using a single cooling system, the operating temperature of the electrically excitable coils and the operating temperature of the power stages can be controlled at the same time, even if these operating temperatures differ.

In accordance with the present disclosure, a single power stage may comprise a H-bridge composed of four power transistors, such as power Field Effect Transistors or Insulated Gate Bipolar Transistors, wherein the output of the H-bridge is directly connected to an excitable coil. A brushless electric motor is also known as an electronically commutated motor, which is a synchronous motor that is powered by a Direct Current, DC, electric source via power stages, which produce an AC electric signal to drive the coils and thus the motor. In this context, AC, alternating current, does not imply a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform. Additional sensors and electronics eventually control the outputs of the power stages in their amplitude, waveform and frequency, i.e. rotor speed.

The rotor of a Switched Reluctance Motor, SRM, system typically does not comprise a plurality of permanent magnets.

Further, the disclosure is directed to a Switched Reluctance Motor, SRM, system. In accordance with the present invention, the Switched Reluctance Motor, SRM, system may also be used as a generator for generating electrical power. The Switched Reluctance Motor, SRM, system may also be used as a combined motor and generator in one.

In an example, the stator comprising said plurality of stator teeth has a predefined radius, wherein said heat resistance inserts are connected to said base cooling plate in a circular manner having a substantially same predefined radius as said stator, wherein the number of heat resistance inserts equals the number of electrically excitable coils, respectively. A single heat resistance insert is thus used per electrically excitable coil, such that each electrically excitable coil has its own insert via which the heat is transferred to the base cooling plate.

Here, the plurality of power stages may be connected to the base cooling plate via a surface area inside a circle spanned by said plurality of heat resistance inserts.

As such, the power stages are situated in such a way that they are comprised within the circle spanned by the coils, i.e. in the middle of the coils. This proved to be an efficient way of placing the power stages. The advantage hereof is that the Switched Reluctance Motor, SRM, system is compact. Further, the use of a single cooling system is here even more beneficial as the power stages are spaced closed to the electrically excitable coils. This makes the manufacturing of the inserts even more simple, as the cooling plate can be placed adjacent to the power stages as well as adjacent to the electrically excitable coils.

The concept is new and inventive compared to the prior art as in the prior art the power stages are not placed within the vicinity of the coils, thereby making the use of a single cooling system more difficult. The inventor found that the power stages can be placed close to the electrically excitable coils, such that the cooling plate can cool the coils as well as the power stages at the same time. In order to get to the coils, and to amend the amount of cooling of the coils, inserts are used which are placed against the coils as well as against the cooling plate.

In an example, the heat resistance inserts comprise solid spacing blocks of a material comprising any of aluminium, stainless steel, etc.

Here, the solid spacing blocks may be provided with through holes for reducing the thermal conductivity thereof.

The inventor has found that the type of material used for the heat resistance inserts does not need to be a thermal isolator. The key aspect of the invention is that a thermal bridge is obtained between the coils and the cooling plate such that the coils are cooled less compared to the power stages. Depending on the length of the inserts and the type of material of the inserts, different operating temperatures of the coils can be obtained.

In another example, the substantially flat hollow main cool body comprises an inlet and an outlet, both provided at a second flat surface of said hollow main cool body, for inputting and outputting said medium, respectively.

The advantage of this example is that the risk of a leak, for example when using water as a cooling medium, in the inlet or outlet will not affect the power stages and/or electronics provided to control the power stages as these are connected to the base cooling plate which is connected to the main cool body at a first flat surface thereof.

The risk of water getting to the power stages and/or the electronics provided to control the power stages, in case of a leak in the inlet and/or outlet, is thus reduced significantly in case the inlet and the outlet are provided another flat side of the hollow main cool body as compared to the case cooling plate.

It is noted that the inlet may be provided in substantially a centre point of said circle. That is, the inlet may be provided in substantially the middle of the circle spanned by the coils / the inserts.

In a detailed example hereof, the substantially flat hollow main cool body comprises flow channels for supporting the flow of said cooling medium between said inlet and said outlet, wherein said flow channels originate from said inlet and extend radially outwardly.

The advantage hereof is explained as follows. The cooling medium enters the substantially flat hollow main cool body at the centre point thereof and then flows radially outwardly. This means that the cooling medium first encounters the power stages as the power stages are placed within the circle spanned by the inserts. This is beneficial as the power stages need to be cooled more compared to the coils, i.e. the operating temperature of the power stages is lower then the operating temperature of the coils. The cooling medium will, of course, be warmed up by the power stages to a higher temperature. This is, however, not an issue as the warmed up cooling medium is still able to cool the coils as the coils are operating at a higher temperature then the power stages.

It is thus advantageous in case the cooling medium first encounters the power stages and, subsequently, encounters the coils.

The cooling system may comprise said cooling medium, wherein said cooling medium is any of air and water.

According to the present disclosure, the cooling medium may be a gas or a liquid.

The advantage of a gas medium is that only a few components are required and that it is therefore very cost effective to implement. No pump, control unit, pipes and a dispensing system are required for cooling the electric motor system. Further, there is no risk on leakage as no liquid is present in the cooling system. A further advantage is that the amount of maintenance to be performed is reduced due to the absence of moving parts in the cooling system.

The advantage of a liquid medium is that less volume, compared to a gaseous medium, is required to obtain the same level of cooling. A liquid medium is further less depending on, for example, the ambient temperature.

In an example, the electric motor system comprises thirty-six electrically excitable coils and eighteen power stages.

In another example, the cooling plate is connected to said main cool body via a pasta, wherein said base cooling plate is connected to said plurality of power stages via a paste, wherein said heat resistance inserts are connected to said base cooling plate via a paste and wherein said plurality of electrically excitable coils are connected to said heat resistance inserts via a pasta.

In a detailed example, the base cooling plate comprises a heat sink.

In an example, each of the power stages comprises a single half hl-bridge for driving the electrically excitable coils.

An H-bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. These circuits are used in different types of fields to allow electric motors to run forwards and backwards.

In yet another example, the rotor surrounds said stator.

In a second aspect, the disclosure provides in a method of operating a Switched Reluctance Motor, SRM, system according to any of the examples provided above.

In a third aspect, the disclosure provides in a motorized electrical vehicle comprising a Switched Reluctance Motor, SRM, system according to any of the examples as provided above.

The expressions, i.e. the wording, of the different aspects comprised by the Switched Reluctance Motor, SRM, system, the method and the motorized electrical vehicle according to the present invention should not be taken literally. The wording of the aspects is merely chosen to accurately express the rationale behind the actual function of the aspects.

In accordance with the present invention, different aspects applicable to the above mentioned examples of the Switched Reluctance Motor, SRM, system, including the advantages thereof, correspond to the aspects which are applicable to method and/or the motorized electrical vehicle according to the present invention.

The above-mentioned and other features and advantages of the invention will be best understood from the following description referring to the attached drawings. In the drawings, like reference numerals denote identical parts or parts performing an identical or comparable function or operation.

Brief description of the drawings

Figure 1 is a schematic diagram illustrating a particular embodiment of the Switched Reluctance Motor, SRM, system in an example.

Figure 2 is a schematic figure illustrating a stator and power stages in an example.

Figure 3 is a schematic diagram of two possible power stages for driving the coils of the stator.

Figure 4 is a schematic diagram of a Switched Reluctance Motor, SRM, system according to the present invention.

Figure 5 is a schematic layout of a Switched Reluctance Motor, SRM, system according to the present invention.

Detailed description

Figure 1 is a schematic diagram illustrating a particular example of a Switched Reluctance Motor, SRM, system 1 to be used according to the present invention. The actual stator and rotor of the system 1 are not shown, these aspects are shown in figure 2. Figure 1 thus displays the electronic circuitry including the power stages, i.e. Drivers A - E, and the electrically excitable coils which are wound on each of the teeth of the stator, i.e. Coils A - E.

According to the example shown in figure 1, a single master control unit 18 is provided which is arranged for controlling three sub control units 11, 12, 13 based on inputs 17 in said master control unit related to any of speed, torque, accelerator and brake signals. It may be advantageous in case such a master control unit 18 is implemented in such a way that it is capable of detecting any form of malfunctioning in the master control unit 18 itself, and, preferably, is able to repair and/or recover from any error or malfunctioning detected. This improved the reliability and the safety aspects of the motor system 1. The functionality of the master control unit 18 may also be implemented redundantly so that in case of an error or malfunctioning in a part of the system, the remainder of the system 1 is able to take over the corresponding functionality thereby increasing the reliability of the system 1 as a whole.

The Switched Reluctance Motor, SRM, system 1 further comprises three sub control units 11, 12, 13. Each sub control unit 11, 12, 13 is coupled to its own rotor position sensor, not shown, via inputs 14, 15, 16, respectively, for determining a position of the rotor with respect to said stator. This aspect further improves the reliability of the system 1 as a whole, as even in case one of the rotor position sensors fails, the motor 1 is still able to function properly. That is, a malfunctioning in one of the rotor position sensors will lead to a sub control unit 11, 12, 13 to malfunction, i.e. to function improperly. As this specific motor system 1 comprises three sub control units 11, 12, 13, the remaining two sub control units 11, 12, 13, i.e. the sub control units 11, 12, 13 which are operating properly, will make sure that the motor system 1 is at least functioning correctly. This does mean that the motor system 1 has a reduced available power as one of the sub control units 11, 12, 13 is not contributing thereto.

The rotor position sensors are typically comprised of absolute angle sensors. These type of sensors may determine the absolute position of the rotor.

Each of the drivers A - E correspond to the Coils A - E, respectively. That is, each Driver drives a single Coil. As mentioned above the driver is a power stage.

The power stages, i.e. the drivers A - E, and the coils which are wound around the teeth of the stator tend to breakdown the most. As such, the Switched Reluctance Motor, SRM, system 1 is designed in such a way that a failure occurring in these components is not destructive for the functioning in the Switched Reluctance Motor, SRM, system 1 as a whole. This is accomplished, amongst other, by the redundancy aspects of the present example.

As such, it was the insight of the inventor to couple one power stage to one coil. For example, power stage indicated with “Driver A” is coupled to the coil “Coil A” which are controlled using the phase A.

Each power stage “Driver A - E” may comprise a H-bridge for driving a single coil. A H-bridge is an electronic circuit comprising four power transistors or four power Field Effect Transistors, FET, which are controlled by a control signal in such a way that in case a high control signal is supplied a load is coupled to a high input voltage, and in case a low control signal is supplied the load is coupled to a low input voltage. Each of the drivers 8, 9, 10 should be designed in such a way that it is not possible to drive the H-bridge in such a way that both of the four power FET’s are in their conductive state such that a short circuit between the high input voltage and the low input voltage occurs.

So, following the reasoning provided above, only one coil is affected in case a single H-bridge, for example a particular FET thereof, breaks down. The remaining of the coils still function properly thereby contributing to the reliability of the Switched Reluctance Motor, SRM, system 1.

Each of two adjacent coils in the stator are driven such that the induction field of a first coil of the pair adjacent coils is directed oppositely to an induction field of a second coil of the pair.

This aspect may be accomplished by connecting each of the two coils of adjacent coils, for example coils referred to with Coil A and Coil B, wherein each of the two coils of these adjacent coils are wound differently. That is, a first coil, for example coil referred to with Coil A, is wound clockwise and the second coil, i.e. the coil referred to with Coil B, is wound anticlockwise. This accomplishes that, when the corresponding H-bridges drive the coils Coil A and Coil B, the produced induction fields of these two coils are oppositely directed. Effectively, a magnetic north pole and a magnetic south pole are created in such a way.

Based on the above, the Switched Reluctance Motor, SRM, system 1 comprises fifteen electrically excitable coils wound on the teeth of the stator, and twelve teeth comprised by the rotor.

Figure 2 is a schematic figure illustrating a stator 51 and corresponding rotor 81 according to the present example.

In this particular example, the stator 51 is designed in such a way that a rotor 81 is to surround the stator 51. The stator 51 comprises a plurality of stator teeth 52, wherein electrically excitable coils are wound on each of those teeth 52. Here, the stator 51 comprises exactly fifteen stator teeth 52, divided in to three groups 53 of three teeth 52 each. The groups 53, and thus also the stator teeth 52 comprised by the groups 53, are placed, i.e. oriented, adjacently to each other along a circumference of the rotor 51. The electrically excitable coils, i.e. the ones referred to with references A-B-C-D-E, are to generate magnetic induction fields for interaction with rotor teeth of the rotor. This causes the rotor 81 to rotate with respect to the stator 51.

The stator teeth 52 may comprise a magnetic core for enhancing the produced magnetic field. The shape of any of the stator teeth 52 is such that a magnetic field produced by a coil wound on such teeth 52 is directed radially with respect to an inner axis of the stator 51.

It is noted that, in this respect, the power stages are to be connected to the coils A-B-C-D-E as indicated with the “X” or having reference numeral 106, respectively. Multiple implementations of these power stages 106 exist which are elaborated in more detail with respect to figure 3.

Figure 3 shows two implementations of power stages 111, 112 that are suitable to be used in accordance with the present disclosure.

The implementation as indicated with reference numeral 11 is called an asymmetric bridge converter and the implementation as indicated with reference numeral 112 is called a H-bridge. Both of these types of implementations may be suitable to be used in combination with the architecture described herein.

Figure 4 is a schematic layout of a Switched Reluctance Motor, SRM, system according to the present disclosure.

Here, a Switched Reluctance Motor, SRM, system 101 having integrated power stages is shown. The invention is displayed as a schematic diagram as to explain the functionality. The actual stator and rotor of the system 101 are not shown.

The Switched Reluctance Motor, SRM, system comprise a rotor comprising a plurality of rotor teeth and a stator comprising a plurality of teeth placed adjacently to each other, wherein electrically excitable coils are wound on each of said teeth, respectively, for generating an induction field for interaction with said teeth of said rotor to cause said rotor to rotate with respect to said stator.

Further, a plurality of power stages 106, such as H-bridges, are provided, wherein each power stage is arranged to drive a single coil of said coils wound on said plurality of teeth. In the present example, the electric motor system 101 comprises fifteen excitable coils and thus also fifteen 106, wherein each power stage comprises a H-bridge and thus four power Metal Oxide Semiconductor, MOS, Field Effect Transistor’s, FETs. It are these MOSFET’s that need to be cooled efficiently by the cooling system according to the present invention.

In figure 4 is the cooling system shown, which comprises a substantially flat hollow main cool body 110 arranged to support the flowing of a cooling medium inside said hollow main cool body for cooling said main cool body, a base cooling plate 108 connected to a first flat surface of said hollow main cool body and to said plurality of power stages for transferring heat between said plurality of power stages and said base cool plate, heat resistance inserts 104 connected to said base cooling plate and said plurality of electrically excitable coils 102 for transferring heat between said plurality of coils and said base cooling plate 108,

The heat resistance inserts 104 provide for a thermal conductivity, thereby creating a thermal buffer such that said electrically excitable coils 102 are cooled less compared to said power stages 106, by said cooling system.

In the present example, the cooling medium is of a temperature close to about 50 degrees Celsius. The operating temperature of the MOSFET’s is about 60 degrees Celsius. The MOSFET’s are directly connected to the base cooling plate 108 in order to obtain sufficient cooling for the MOSFET’s to their operating temperature. The operating temperature of the coils is about 90 degrees Celsius, i.e. much higher compared to the operating temperature of the MOSFET’s. As such, the inventor has found to provide inserts 104 between the coils 102 and the base cooling plate 108, such that a single cooling system can be used for cooling the MOSFET’s to about 60 degrees Celsius and the coils 102 to about 90 degrees Celsius. The inserts 104 thus provide for a thermal conductivity, thereby creating a thermal buffer such that the electrically excitable coils 102 are cooled less compared to the power stages 106, by the cooling system.

Pasta’s 103, 105, 109, 107 may be used to connect each of the above mentioned elements firmly to each other, such that heat transfer between these elements is improved.

Figure 5 is a schematic layout of a Switched Reluctance Motor, SRM, system 201 according to the present invention. Here, the hollow main cool body 202, the base cooling plate 204, the heat resistance inserts 203, the electrically excitable coils 206, the power stages 205 are indicated in a layout position so that it is clear how the elements are oriented with respect to each other.

The power stages 205, i.e. the MOSFET’s as indicated above, are placed on a printed circuit board, PCB, 209, which further comprises the control logic for controlling the MOSFET’s. The coils 206 are wound on the teeth 210 of the stator for generating an induction field for interaction with the plurality of rotor teeth 208 to cause the rotor to rotate with respect to the stator.

Clauses

Clause 1. A Switched Reluctance Motor, SRM, system having integrated power stages, said electric motor system comprising: a rotor comprising a plurality of rotor teeth; a stator comprising a plurality of teeth placed adjacently to each other, wherein electrically excitable coils are wound on each of said teeth, respectively, for generating an induction field for interaction with said plurality of rotor teeth to cause said rotor to rotate with respect to said stator, a plurality of power stages, such as H-bridges, wherein each power stage is arranged to drive a single coil of said coils wound on said plurality of teeth; a cooling system comprising: a substantially flat hollow main cool body arranged to support the flowing of a cooling medium inside said hollow main cool body for cooling said main cool body; a base cooling plate connected to a first flat surface of said hollow main cool body and to said plurality of power stages for transferring heat between said plurality of power stages and said base cool plate; heat resistance inserts connected to said base cooling plate and said plurality of electrically excitable coils for transferring heat between said plurality of coils and said base cooling plate, wherein said heat resistance inserts provide for a thermal conductivity, thereby creating a thermal buffer such that said electrically excitable coils are cooled less compared to said power stages, by said cooling system.

Clause 2. A Switched Reluctance Motor, SRM, system according to clause 1, wherein said stator comprising said plurality of teeth has a predefined radius, wherein said heat resistance inserts are connected to said base cooling plate in a circular manner having a substantially same predefined radius as said stator, wherein the number of heat resistance inserts equals the number of electrically excitable coils, respectively.

Clause 3. A Switched Reluctance Motor, SRM, system according to clause 2, wherein said plurality of power stages are connected to the base cooling plate via a surface area inside a circle spanned by said plurality of heat resistance inserts.

Clause 4. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said heat resistance inserts comprise solid spacing blocks of a material comprising any of aluminium and stainless steel.

Clause 5. A Switched Reluctance Motor, SRM, system according to clause 4, wherein said solid spacing blocks are provided with through holes for reducing the thermal conductivity thereof.

Clause 6. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said substantially flat hollow main cool body comprises an inlet and an outlet, both provided at a second flat surface of said hollow main cool body, for inputting and outputting said medium, respectively.

Clause 7. A Switched Reluctance Motor, SRM, system according to clause 6 and 3, wherein said inlet is provided in substantially a centre point of said circle.

Clause 8. A Switched Reluctance Motor, SRM, system according to clause 7, wherein said substantially flat hollow main cool body comprises flow channels for supporting the flow of said cooling medium between said inlet and said outlet, wherein said flow channels originate from said inlet and extend radially outwardly.

Clause 9. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said cooling system comprises said cooling medium, wherein said cooling medium is any of air and water.

Clause 10. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said electric motor system comprises thirty-six electrically excitable coils and eighteen power stages.

Clause 11. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said base cooling plate is connected to said main cool body via a pasta, wherein said base cooling plate is connected to said plurality of power stages via a paste, wherein said heat resistance inserts are connected to said base cooling plate via a paste and wherein said plurality of electrically excitable coils are connected to said heat resistance inserts via a pasta.

Clause 12. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said base cooling plate comprises a heat sink.

Clause 13. A Switched Reluctance Motor, SRM, system according to any of the previous clauses, wherein said rotor surrounds said stator.

Clause 14. A method of operating a Switched Reluctance Motor, SRM, system according to any of the previous clauses.

Clause 15. A motorized electrical vehicle comprising a Switched Reluctance Motor, SRM, system according to any of the clauses 1-13.

The present invention is not limited to the embodiments, the clauses and/or the examples as disclosed above, and can be modified and enhanced by those skilled in the art beyond the scope of the present invention as disclosed in the appended claims without having to apply inventive skills.

Claims (11)

A switched reluctance motor, SRM, short-flux path system, comprising: - a rotor comprising a plurality of rotor teeth; - a stator comprising at least three juxtaposed groups of at least three phases each, wherein each phase is associated with one stator tooth of the stator within a corresponding group, wherein electrically excitable coils are wound on each stator tooth, respectively, thereby providing single phase coils for generating induction fields to provide short flux paths in interaction with the rotor teeth to cause the rotor to rotate with respect to the stator, in which each group is associated with at least three power stages contained by the motor system, such as h- bridges, in which each power stage is arranged to control a single phase coil such that adjacent coils of the rotor provide oppositely directed induction fields. The switched reluctance motor, SRM, system of claim 1, wherein the stator comprises at least three adjacent groups of at least five phases each. 3. Switched reluctance motor, SRM, system according to one of the preceding claims, wherein each adjacent coil placed is wound in opposite directions. A switched reluctance motor, SRM, system according to any of claims 1 to 2, wherein each adjacent placed coil is wound in the same direction, and wherein each adjacent placed coil is oppositely controlled by the corresponding h-bridge. A switched reluctance motor, SRM, system according to any one of the preceding claims, wherein the system comprises at least three substitute units, wherein each substitute unit is associated with power stages of a particular group, wherein each substitute unit is adapted to actuate the corresponding power stages. The switched reluctance motor, SRM, system of claim 5, wherein each of the substitute units includes its own rotor position sensor for determining the position of the rotor with respect to the stator. The switched reluctance motor, SRM, system of claim 6, wherein the switched reluctance motor, SRM, system further comprises a master control unit adapted to control the three substitute units based on inputs to the master control unit related to a speed, torque, acceleration, and brake signals . A switched reluctance motor, SRM, system according to any of the preceding claims, wherein the router surrounds the stator. The switched reluctance motor, SRM, system according to any of claims 1 to 7, wherein the stator surrounds the rotor. 10. Method of operating a switched reluctance motor, SRM, system according to one of the preceding claims. A motorized electric vehicle comprising a switched reluctance motor, SRM, system according to any of claims 1 to 9.