Patent Description:
Switched reluctance machines (SRMs) are becoming increasingly popular as variable speed drives. Principally, this is because SRMs are simple to build and inexpensive, at least when compared to more commonly used motors. However, SRMs are underutilised for commercial applications, as they typically exhibit high torque ripple and require non-standard asymmetric half bridge converters. <NPL> discloses an embodiment of a recently proposed drive configuration which allows an SRM having six phases A, B, C, D, E, F to be driven by an standard three-phase AC inverter. A plurality of diodes having electrical connections are arranged alternatively between the output phases of the power converter to convert the bipolar current waveform output from each phase of the three-phase converter into two unipolar half waveforms, relating to the positive and negative regions of the waveform, respectively. This enables the three-phase inverter to operate as it would for a three-phase electric machine, while supplying a six-phase SRM and having only three power connections between the inverter and the motor. The increased number of phases permits low torque ripple and the diode arrangement allows use of standard full bridge converters. However, further improvements to the proposed drive configuration are required to improve the suitably of SRMs for commercial applications, particularly hybrid electric vehicles (HEVs) and electric vehicle (EVs). Earlier patent application <CIT> discloses an electric machine, a power converter and a single cooling loop. A switched reluctance machine with diodes is also shown in <CIT>.

The invention is defined in appended claim <NUM>.

Herein is also disclosed an electrical sub-assembly comprising: a stator having a plurality of coils; cooling means attached to the stator; and a plurality of pairs of diodes attached to the cooling means, each pair of diodes being in antiparallel configuration and having three electrical terminals, one of the three electrical terminals being a common terminal shared by both diodes in each pair of diodes, wherein the cooling means is configured to, in use, simultaneously cool the stator and the plurality of diodes. The invention may advantageously enable mounting of the diodes to the cooling means. Additionally, the invention may reduce the number of electrical components, e.g. busbars, required to connect the drive configuration to the coils of the stator.

According to the invention, the electrical sub-assembly further comprises a plurality of busbars electrically connecting each of the diodes to at least one of the plurality of coils via one or more of the electrical terminals.

In certain embodiments, one or more of the plurality of pairs of diodes may each be formed as a single electrical component in which a single pair of diodes is packaged.

In certain embodiments, one or more of the plurality of pairs of diodes may together be formed as a single electrical component in which multiple pairs of diodes are packaged.

In certain embodiments, at least two of the plurality of pairs of diodes may be electrically connected to one another by an electrical connection within the single electrical component.

In certain embodiments, the common terminals of the plurality of pairs of diodes may each electrically connected to a respective one of the plurality of busbars. In certain embodiments, n pairs of diodes may be electrically connected to 3n busbars. In certain embodiments, three of pairs of diodes may be electrically connected to nine busbars.

In certain embodiments, two or more of the common terminals of the plurality of pairs of diodes may together be electrically connected to one of the plurality of busbars. In certain embodiments, n pairs of diodes may be electrically connected to 3n-<NUM> busbars. In certain embodiments, three of pairs of diodes may be electrically connected to eight busbars. In certain embodiments, n pairs of diodes may be electrically connected to 3n-<NUM> busbars. In certain embodiments, three of pairs of diodes may be electrically connected to seven busbars.

There is provided an electrical sub-assembly comprising a stator having a plurality of coils; cooling means attached to the stator; a plurality of diodes attached to the cooling means, each of diodes being electrically connected to a respective one of the plurality of coils; and a plurality of busbars, each busbar being electrically connected to one or more of the plurality of diodes and/or one or more of the plurality of coils, wherein the cooling means is configured to, in use, simultaneously cool the stator and the plurality of diodes.

In certain embodiments, the plurality of diodes may comprise at least twelve diodes, the total number of diodes being a multiple of six.

In certain embodiments, the plurality of busbars may comprise a first busbar, a second busbar and a third busbar. In certain embodiments, n/<NUM> of the plurality of diodes and respective coils may electrically connect the first and second busbars, a further n/<NUM> of plurality of diodes and respective coils may electrically connect the first and third busbars, and the remaining n/<NUM> of the plurality of diodes and respective coils may electrically connect the second and third busbars.

In certain embodiments, the plurality of busbars further comprises a fourth busbar. In certain embodiments n/<NUM> of the plurality of diodes and respective coils may electrically connect the first and second busbars, a further n/<NUM> of plurality of diodes and respective coils may electrically connect the third and second busbars, and the remaining n/<NUM> of the plurality of diodes and respective coils may electrically connect the fourth and second busbars.

In certain embodiments, the cooling means comprises a casing. In certain embodiments the cooling means may at least partially surrounds the stator. In certain embodiments, the cooling means may be configured to receive a supply of cooling fluid.

There is provided an electric machine comprising the electrical sub-assembly as described above.

In certain embodiments, the electric machine may be a motor, and optionally the motor has at least six-phases. In certain embodiments, the electric machine may be a generator, and wherein optionally motor has at least six-phases.

There is provided a vehicle comprising an electric machine as described above.

Electrical sub-assemblies will now be described by way of example only, with reference to the accompanying figures, in which:.

The specific drive configurations and electrical sub-assemblies shown in <FIG>, <FIG>, <FIG>, <FIG> are outside the scope of the appended claims.

An electrical sub-assembly will now be described with reference to <FIG>. <FIG> shows a schematic of a drive configuration <NUM> for a six-phase switched reluctance machine (SRM), specifically a switched reluctance motor, having six phases A, B, C, D, E, F. The sub-assembly comprises a stator having a plurality of coils <NUM> and a cooling means attached, e.g. mounted, to the stator. In certain embodiments, the cooling means may comprise a cooling jacket (which may be referred to as a water jacket). The cooling means may be configured such that, in use, the cooling means cools the stator. In certain embodiments, the cooling means may comprise a casing, a fluid inlet and a fluid outlet. The cooling means may at least partially surround the stator and/or may be a cylindrical casing. In use, a pressurised cooling fluid, e.g. water or oil, may be supplied to the casing through the fluid inlet to circulate through the casing before being discharged therefrom via the fluid outlet. While circulating through the casing, the cooling fluid may absorb heat from the stator, thus cooling stator. In certain embodiments, the cooling means may comprise a Peltier cooler, i.e. a thermoelectric cooler. In certain embodiments, the cooling means may comprise oil cooling applied directly to the coils <NUM> and the diodes <NUM>, i.e. a flooded motor.

The electrical sub-assembly further comprises a plurality of pairs of diodes <NUM> attached, e.g. mounted, to the cooling means. In certain embodiments, the electrical sub-assembly may comprise three pairs of diodes <NUM>. The diodes <NUM> are attached to the cooling means such that, in use, the cooling means is capable of cooling the diodes <NUM>. Therefore, in use, the cooling means may simultaneously cool both the stator and the diodes <NUM>. Each pair of diodes <NUM> is in antiparallel configuration, i.e. electrically connected in parallel such that electrical current may flow through a pair of diodes <NUM> in opposing directions by flowing either in a first direction via a first diode <NUM> in pair of diodes <NUM> or a second opposing direction via a second diode <NUM> in pairs of diodes <NUM>. Additionally, each pair of diodes <NUM> has three electrical terminals <NUM>. Of the three electrical terminals <NUM> of each pair of diodes <NUM>, one of the three electrical terminals <NUM> is a common terminal <NUM> electrically connected to both diodes <NUM> in a pair of diodes <NUM>, i.e. each common terminal <NUM> is shared by both diodes <NUM> in a pair of diodes <NUM>. Accordingly, two of the three electrical terminals <NUM> of each pair of diodes <NUM> may be electrically connected to only one of the two diodes <NUM> in a pair of diodes <NUM> (although in addition to other components in the drive configuration <NUM>).

The electrical sub-assembly may further comprise a plurality of busbars <NUM> electrically connecting each of the diodes <NUM> to at least one of the plurality of coils <NUM>. The electrical connection between the diodes <NUM> and one or more of the plurality of coils <NUM> is via a respective electrical terminal <NUM>. Further busbars <NUM> may connect a number of the plurality of coils to one another. The busbars may take the form of conducting rings attached to the electrical sub-assembly.

The drive configuration <NUM> may be electrically connected to a power converter <NUM> having a plurality of output phases. In certain embodiments, the drive configuration <NUM> may be connected to a three-phase power converter, e.g. a full bridge converter, having three output phases. Power connections <NUM> may electrically connect the power converter <NUM> and the drive configuration <NUM> to one another. Specifically, each of the power connections <NUM> may electrically connect to a respective one of the plurality of diodes <NUM>. Each of the power connections <NUM> may correspond to an output phase of the converter <NUM>, thus each of the pairs of diodes <NUM> may be electrically connected in line with one of the plurality of output phases of the power converter <NUM>. A first pair of diodes <NUM> may be associated with phases A and D of the SRM and may relate to a first output phase of the power converter <NUM>. A second pair of diodes <NUM> may be associated with phases B and E of the SRM and may relate to a second output phase of the power converter <NUM>. A third pair of diodes <NUM> may be associated with phases C and F of the SRM and may relate to a third output phase of the power converter <NUM>. Further busbars <NUM> may connect one or more of the plurality of coils to one or more of the power connections <NUM>.

Arranged in this manner, the pairs of diodes <NUM> may convert a bipolar current waveform output from each of the outputs phases of the power converter <NUM> into two unipolar half waveforms, each relating to a positive region and a negative region of the waveform, respectively. Consequently, the converter power converting <NUM> having n output phases is able to supply a SRM having 2n phases, while having only n power connections <NUM> between the power convertor <NUM> and the drive configuration <NUM>, where n is an integer equal to or greater than one. For example, in embodiments where power converter <NUM> has three output phases, the power converter is able to supply a SRM having six phases, while having only three power connections <NUM> between the power convertor <NUM> and the drive configuration <NUM>.

One or more of the plurality of pairs of diodes <NUM> may each be formed as a first diode unit <NUM>, i.e. a single electrical component in which a single pair of diodes <NUM> is packaged. Each of the diode units <NUM> may comprise the electrical terminals <NUM> of the diodes <NUM> packaged therein.

In certain embodiments, the drive configuration <NUM> may be a delta type configuration, as illustrated in <FIG>. Referring to the drive configuration <NUM> illustrated in <FIG>, the common terminals <NUM> of the plurality of pairs of diodes <NUM> may each be electrically connected to a respective one of the plurality of busbars, i.e. for each electrical terminal <NUM> there is one busbar connecting the diodes <NUM> to the coils. For example, there may be three pairs of diodes <NUM>, thus nine electrical connections <NUM> each connected to at least one of nine busbars, respectively. This example is possible using the drive configuration <NUM> illustrated in <FIG>.

<FIG> shows a schematic of a drive configuration <NUM> of a further embodiment not belonging to the invention, with reference numerals offset by a factor of <NUM> identifying like features discussed above with reference to <FIG>. One or more of the plurality of pairs of diodes <NUM> may together be formed as a second diode unit <NUM>, i.e. a single electrical component in which a multiple pairs of diodes <NUM> are packaged. In certain embodiments, the second diode unit <NUM> may comprise a plurality of first diode units <NUM> (see <FIG>). The second diode unit <NUM> may comprise the electrical terminals <NUM> of the pairs of diodes <NUM> packaged therein.

<FIG> shows a schematic of a drive configuration <NUM> of a further embodiment not belonging to the invention, with reference numerals offset by a factor of <NUM> identifying like features discussed above with reference to <FIG>. In certain embodiments, the drive configuration <NUM> may be a star type configuration, as illustrated in <FIG>. Referring to drive configuration <NUM> illustrated in <FIG>, two or more the common terminals <NUM> of the plurality of pairs of diodes <NUM> may together be electrically connected to one of the plurality of busbars <NUM>, i.e. two or more the common terminals <NUM> may be electrically connected to the same busbar <NUM>. Thus, in certain embodiments, there is at least one fewer busbars connecting the diodes <NUM> to the coils than the number of electrical connections <NUM>. For example, there may be three pairs of diodes <NUM>, thus nine electrical connections <NUM> connected to seven busbars <NUM>, with the respective three common terminals <NUM> being connected to one busbar <NUM>. This example is possible using the drive configuration <NUM> illustrated in <FIG>.

<FIG> shows a schematic of a drive configuration <NUM> of an embodiment according to the invention, with reference numerals offset by a factor of <NUM> identifying like features discussed above with reference to <FIG>. As illustrated in <FIG>, an internal electrical connection <NUM> within the second diode unit <NUM> electrically connects at least two pairs of diodes <NUM>. Consequently, two pairs of diodes <NUM> share a common terminal <NUM>. The internal electrical connection <NUM> may enable delta type drive configurations, as illustrated in <FIG>, to have to least one fewer busbars <NUM> connecting the diodes <NUM> to the coils than the number of electrical connections <NUM>, i.e. two or more of the common terminals <NUM> may be electrically connected to the same busbar <NUM>. For example, there may be three pairs of diodes <NUM>, thus nine electrical connections <NUM> connected to seven busbars <NUM>, with the two of the three common terminals <NUM> being connected to one busbar <NUM>. This example is possible using the drive configuration <NUM> illustrated in <FIG>. While star type drive configurations advantageously have no third harmonic currents, delta type connections may be used in preferred embodiments of the invention to minimise diode current rating and diode size and cost.

An electrical sub-assembly according to further embodiment not belonging to the invention will now be described with reference to <FIG> shows a schematic of a partial drive configuration <NUM> for a six-phase switched reluctance machine (SRM), specifically a switched reluctance motor. The sub-assembly comprises a stator having a plurality of coils <NUM> and a cooling means attached, e.g. mounted, to the stator. The cooling means may be as described above. The electrical sub-assembly further comprises a plurality of diodes <NUM> attached, e.g. mounted, to the cooling means. Each of diodes <NUM> may be electrically connected to a respective one of the plurality of coils <NUM>.

The electrical sub-assembly further comprises a plurality of busbars <NUM>, each busbar being electrically connected to one or more of the plurality of diodes <NUM> and/or one or more of the plurality of coils <NUM>. As above, the cooling means is configured to, in use, simultaneously cool the stator and the plurality of diodes <NUM>.

While only two diodes <NUM> and their respective coils <NUM> are illustrated in <FIG>, the plurality of diodes <NUM> may comprise any number of diodes <NUM> greater than or equal to twelve diodes <NUM>, as long as the total number of diodes <NUM> is a multiple of six. Referring the drive configuration <NUM> illustrated in <FIG>, n/<NUM> of the plurality of diodes <NUM> and respective coils <NUM> may electrically connect a first busbar <NUM> and a second busbar <NUM> to one another. A further n/<NUM> of plurality of diodes <NUM> and respective coils <NUM> may electrically connect a third busbar <NUM> and the second busbar <NUM> to one another. The remaining n/<NUM> of the plurality of diodes <NUM> and respective coils <NUM> may electrically connect the fourth and second busbars. The drive configuration <NUM> illustrated in <FIG> may be a star type configuration. Half of the plurality of diodes <NUM> and respective coils <NUM> connecting one busbar <NUM> with another may allow electrical current to flow in a first direction, e.g. from the first busbar <NUM> to the second busbar <NUM>, and the remaining half may allow electrical current to flow in a second opposing direction, e.g. from the second busbar <NUM> to first busbar <NUM>.

<FIG> shows a schematic of a partial drive configuration <NUM> of a further embodiment not belonging to the invention, with reference numerals offset by a factor of <NUM> identifying like features discussed above with reference to <FIG>. While only two diodes <NUM> and their respective coils <NUM> are illustrated in <FIG>, the plurality of diodes <NUM> may comprise any number of diodes <NUM> greater than or equal to twelve diodes, as long as the total number of diodes <NUM> is a multiple of six. Referring the drive configuration <NUM> illustrated in <FIG>, n/<NUM> of the plurality of diodes <NUM> and respective coils <NUM> electrically may connect a first busbar <NUM> and a second busbar <NUM> to one another, where n is a integer equal to or greater than twelve and is a multiple of six. A further n/<NUM> of plurality of diodes <NUM> and respective coils <NUM> may electrically connect the first busbar <NUM> and a third busbar <NUM> to one another. The remaining n/<NUM> of the plurality of diodes <NUM> and respective coils <NUM> may electrically connect the second busbar <NUM> and the third busbar <NUM> to one another.

The drive configuration <NUM> illustrated in <FIG> may be a delta type configuration. As above, Half of the plurality of diodes <NUM> and respective coils <NUM> connecting one busbar <NUM> with another may allow electrical current to flow in a first direction, e.g. from the first busbar <NUM> to the second busbar <NUM>, and the remaining half may allow electrical current to flow in a second opposing direction, e.g. from the second busbar <NUM> to the first busbar <NUM>.

In certain embodiments, the electrical sub-assembly has particular application in a traction motor for use in a vehicle, for example a hybrid electric vehicle (HEV) or an electric vehicle (EV). Certain embodiments of the invention enable mounting of the diodes to the cooling means. Certain embodiments of the invention reduce the number of electrical components, e.g. busbars, required to connect the drive configuration to the coils of the stator.

Claim 1:
An electrical sub-assembly comprising:
a stator having a plurality of coils (<NUM>);
a plurality of pairs of diodes (<NUM>), each pair of diodes having a first diode and a second diode in antiparallel configuration in which the first diode and the second diode are electrically connected in parallel such that, in use, electrical current flows through the pair of diodes (<NUM>) in opposing directions by flowing either in a first direction via the first diode or a second opposing direction via the second diode and each pair of diodes having three electrical terminals (<NUM>); and
a plurality of busbars (<NUM>) electrically connecting each of the diodes to at least one of the plurality of coils via one or more of the electrical terminals,
wherein one of the three electrical terminals (<NUM>) is a common terminal (<NUM>) shared by both diodes (<NUM>) in each pair of diodes, and two of the pairs of diodes share one of the common terminals.