GB2608623A

GB2608623A - Resonant electrical machine

Info

Publication number: GB2608623A
Application number: GB2109746.4A
Authority: GB
Inventors: Deodhar Rajesh
Original assignee: IMRA Europe SAS
Current assignee: IMRA Europe SAS
Priority date: 2021-07-06
Filing date: 2021-07-06
Publication date: 2023-01-11
Anticipated expiration: 2041-07-06
Also published as: GB2608623B; GB202109746D0

Abstract

Driving circuitry for a stator of an electrical machine includes a first winding 526 and a first capacitor 523 arranged in series with one another in a first branch and arrange in parallel with a second winding 524. The driving circuitry further includes a second capacitor 525 arranged in series with both the first and second windings. The combination of the second capacitor and the second winding may have an electromagnetic resonant frequency. The driving circuitry may be compatible with a single‐phase AC power supply 522 to generate increased output torque at a particular driving frequency. A switch 529 may be arranged to connect the first branch to the power supply. The switch may be a centrifugal switch configured to disconnect the first winding and the first capacitor from the power supply based on a rotational speed of a rotor of the electrical machine. The rotor may be a squirrel-cage rotor and may have an air-core or a core formed of a magnetic material.

Description

Resonant Electrical Machine

Field of the Invention

The invention relates generally to electrical machines, stators for electrical machines, and driving circuitry for stators of electrical machines. More specifically, the electrical machines of the present invention are resonant electrical machines capable of operating using only a single-phase power supply.

Background

Electrical machines can take many forms to serve many different purposes. For example, electric motors can be used to provide an output torque in response to a supply of electrical energy, while electric generators can produce electrical energy in response to an input torque. Furthermore, electric motors can themselves take many different forms. For example, an electric motor could be powered by either AC or DC current, and even an AC motor can take multiple forms, such as an induction motor or a synchronous electric motor.

Induction motors have many different applications. For example, induction motors can be utilised in motor vehicles, aeroplanes, and other similar applications, as well as smaller-scale applications such as household fans, washing machines, household pumps, industrial low-power pumps, and low-power machining equipment. Due to this broad range of possible applications, induction motor technology has diverged according to the particular use case.

For example, larger-scale applications with higher loads often use three-phase induction motors, where a three-phase power supply is arranged to produce a rotating magnetic field to drive rotation of a rotor. In contrast, for smaller loads single-phase induction motors are often used, where an oscillating magnetic field is generated from a single-phase power supply.

Three-phase induction motors are significantly more complex and costly than their single-phase counterparts and as a result are an area of far more active research than single-phase induction motors. However, the present inventors have identified an improved arrangement for that allows single-phase induction motors to have significantly reduced size and weight, as well as providing the possibility of increased output torque.

Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

According to a first aspect, there is provided driving circuity for a stator for an electrical machine, the driving circuitry comprising: a first winding; a first capacitor arranged in series with the first winding; a second winding arranged in parallel with the first winding and the first capacitor; and a second capacitor arranged in series with: the first winding and the first capacitor, and the second winding.

In this manner, a resonant electrical machine is provided, yielding increased output torque at a given driving frequency and also allowing the electrical machine to be manufactured with reduced size and weight, without compromising on overall output torque.

Advantageously, a capacitance of the second capacitor and an inductance of the second winding may be selected such that combination of the second capacitor and the second winding have an electromagnetic resonant frequency. As such, the electromagnetic resonant frequency may be set to be close to a desired operating frequency, such that the benefit of increased output torque is realised at the desired operating frequency.

Advantageously, the driving circuitry is configured to be electrically connected to a single-phase power supply. In this manner, the electrical machine may be a single-phase resonant electrical machine. Accordingly, fewer capacitors are required (only two are required, as compared to at least three, and possibly six if also connected in the rotor circuit, for a three-phase induction machine), resulting in a cheaper and less complex design. Furthermore, in the event that the electrical machine operates from a DC power source, an H-bridge circuit may be used to generate the required AC current, rather than a three-phase inverter. Accordingly, fewer switches are required, reducing cost.

In some aspects, the driving circuitry may be considered to include the single-phase power supply. The single phase power supply may include circuitry for converting DC current to AC current (such as an H-bridge circuit), which may additionally in some cases be considered to include a source of DC power, such as a battery.

Advantageously, the first winding and the first capacitor may be arranged in series in a first branch of the driving circuity; the second winding is arranged on a second branch of the driving circuitry; wherein the first branch and the second branch are arranged in parallel with one another, and wherein the second capacitor is arranged in series with the first branch and the second branch.

Accordingly, the arrangement of the second capacitor in this way provides the benefits of a resonant electrical machine, without a large increase in the complexity of the driving circuitry of a single-phase electrical machine.

In some aspects, the first branch further includes a switch arranged to switchably couple the first branch to a single-phase power supply. Accordingly, the first branch may be decoupled from the power supply once it is no longer required, in order to conserve electrical power.

Advantageously, the switch may be a centrifugal switch configured to decouple the first branch from the single-phase power supply based on a rotational speed of a rotor of the electrical machine. Accordingly, the first branch may be utilised to start the electrical machine and then automatically decoupled from the power supply once the rotor has reached a particular rotational speed, thereby conserving energy.

In some aspects, a capacitance of the second capacitor is between 10microF and 1000microF. Accordingly, when utilised with standard electrical windings, this range of capacitance values allows an electromagnetic resonant frequency to be selected depending on a desired operating frequency of the electrical machine.

According to a second aspect of the invention, there is provided a stator for an electrical machine comprising the driving circuitry as described above. Such a stator may be used in a many types of electrical machine. The driving circuitry may in some cases be mounted onto a body of the stator, or parts of the circuitry may be located separate from, but electrically connected to, the stator body.

According to a third aspect of the invention, there is provided an electrical machine comprising: the stator as described above; and a rotor. Such an electrical machine is able to produce increased output torque at a particular driving frequency and can as a consequence also be made smaller and more lightweight.

In some aspects, the rotor is a squirrel-cage rotor. Accordingly, the electrical machine can be utilised in traditional electrical machines where squirrel-cage rotors may be utilised.

Advantageously, the rotor may be an air-core rotor. As such, the electrical machine may be made more lightweight and smaller in size, without compromising in the overall output torque of the electrical machine. However, in some aspects the rotor may include a core formed of a magnetic material. As such, the magnetic coupling between the rotor and stator may be increased, resulting in greater output torque.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the following figures.

In accordance with one (or more) embodiments of the present invention the Figures show the following: Figure 1 illustrates a resonant three-phase induction motor according to a first comparative example.

Figure 2 illustrates a three-phase inverter according to the first comparative example.

Figure 3 illustrates an induction motor according to a second comparative example.

Figure 4 illustrates an H-bridge inverter according to the second comparative example.

Figure 5 illustrates a resonant single-phase induction motor according to a first example teaching of the disclosure.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Detailed Description

Figure 1 shows a three-phase induction motor 100 and a representation of the circuitry for the three-phase induction motor 100. The three-phase induction motor 100 includes a rotor 110, a stator 130 and an air gap 120 between the rotor 110 and the stator 130.

The stator 130 includes stator windings 131 comprising three winding phases 131a, 131b, 131c each arranged to receive a different phase of a three-phase driving signal generated by an inverter, or by any other suitable known means. In response to a three-phase driving signal, the stator windings 131 produce a rotating magnetic field. The rotor includes rotor windings 111 configured to magnetically couple to the rotating magnetic field produced by the stator windings 131 to cause the rotor to rotate.

The stator windings 131 in Figure 1 are shown spaced apart around the circumference of the stator 130, however in reality the stator windings 131 will be grouped close together in sequence. In other words, stator winding 131a will be located proximal to stator windings 131b, which will in turn be located proximal to stator winding 131c. Stator winding 131c will then be located proximal to another stator winding configured to receive the same phase of the three-phase driving voltage as stator winding 131a. Accordingly, each stator winding is arranged next to two stator windings which each receive a different phase of the three-phase driving voltage and which receive a phase of the three-phase driving voltage different to that particular stator winding. The rotor windings 111a-111c are arranged in a corresponding manner to the stator windings 131a-131c.

The three-phase induction motor 100 of Figure 1 is a resonant induction motor and as such includes a plurality of capacitors 132 arranged in series with the stator windings 131. Capacitor 132a is arranged in series with stator winding 131a, capacitor 132b is arranged in series with stator winding 131b, and capacitor 132c is arranged in series with stator winding 131c. The inductances of the stator windings 131a-131c are equal (or approximately equal) to one another, and the capacitances of the capacitors 132a-132c are equal (or approximately equal) to one another. In this manner, the combination of the stator windings 131 and the capacitors 132 has an electromagnetic resonant frequency, determined by the inductance of the stator windings 131 and the capacitors 132, referred to as the resonant frequency of the stator.

Rotor 110 may also include a plurality of capacitors 112 arranged in series with the rotor windings 111, as shown in Figure 1. Capacitor 112a may be arranged in series with rotor winding 111a, capacitor 112b may be arranged in series with rotor winding 111b, and capacitor 112c may be arranged in series with rotor winding 111c. The inductances of the rotor windings 111a-111c may be equal (or approximately equal) to one another, and the capacitances of the capacitors 112a-112c may be equal (or approximately equal) to one another. In this manner, the combination of the rotor windings 111 and the capacitors 112 may also have an electromagnetic resonant frequency, determined by the inductance of the rotor windings 111 and the capacitors 112, referred to as the resonant frequency of the rotor. Generally, the resonant frequency of the stator is set to be the same as the inverter applied frequency, while the resonant frequency of the rotor is set to be approximately equal to the slip frequency of the rotor.

In use, a three-phase driving signal is provided to the stator windings 131 with a particular frequency called the driving frequency. When the driving frequency is close to the resonant frequencies of the stator 130 and rotor 110, the magnetic coupling between the stator 130 and rotor 110 significantly increases, thereby increasing the output torque of the electrical machine 100.

This increased output torque at the resonant frequency allows the three-phase resonant induction motor 100 to be provided without a ferromagnetic core. That is, traditional induction motors are generally provided with a rotor core formed of a ferromagnetic material (such as iron) in order to increase the magnetic coupling between the rotor and stator, in order to increase the output torque of the motor. However, as the three-phase resonant induction motor 100 can be provided with a driving current at close to the resonant frequency in order to increase the output torque, the presence of a ferromagnetic core is not necessary. Instead, the three-phase resonant induction motor 100 can be provided with a core formed of a non-ferromagnetic material, or with a hollow core (a so-called 'air-core' three-phase resonant induction motor). This allows the size and weight of the three-phase resonant induction motor 100 to be significantly reduced, without compromising on output torque. However, one drawback of three-phase induction motors is the comparatively complicated driving circuitry used to provide the three-phase driving current.

Figure 2 shows the circuitry 200 for a three-phase inverter 220 which converts DC current into a three-phase AC driving current for a three-phase induction motor, such as the three-phase resonant induction motor 100 shown in Figure 1. The circuitry 220 includes a DC power supply 222 (for example a battery) connected to six transistor switches 224a-f. The six transistor switches 224a-f selectively actuate in order to produce a three phase AC current that is supplied to the three-phase resonant induction motor 100, as shown in Figure 1. In particular, the three connections to the three-phase resonant induction motor 100 shown in Figure 2 connect to respective ones of windings 131a, 131b and 131c shown in Figure 1. The requirement for at least three (and in some examples six) capacitors 132a-c in the three-phase induction motor 100 and six transistor switches 224a-f in the three-phase inverter 220 result in a comparatively complex and expensive arrangement, which may be unsuitable for low cost and low torque applications.

Instead, such low cost and low torque applications often use a single-phase induction motor 300, such as that shown in Figure 3. Circuitry 320 includes a single-phase AC power supply 322 provides an AC current to a main winding 324 arranged to produce an oscillating magnetic field in response to an AC current, which drives rotation of a rotor 310 (such as a squirrel-cage rotor). The single-phase AC power supply 322 also provides an AC current to an auxiliary winding 326 arranged in parallel with the main winding 326. Arranged in series with the auxiliary winding 326 is a capacitor 323. This capacitor creates an electrical phase delay between the main winding 324 and the auxiliary winding 326 which allows the rotor 310 be started from a stationary winding. The branch of the circuitry 320 including the auxiliary winding 326 and the capacitor 323 may also include a switch 329 (such as a centrifugal switch) that is arranged to disconnect said branch from the power supply 322 once the rotor has reached a particular rotational speed, while leaving the branch including the main winding 324 connected to the power supply 322.

In order to provide the single-phase AC power supply, an H-bridge circuit is sometimes used to convert a DC power supply to the single-phase AC supply 322 required for the circuitry 320 in Figure 3. Figure 4 shows an example of such an H-bridge circuit 400. A DC power supply 422 (for example a battery) is electrically connected to four transistor switches 424a-d which selectively actuate to provide an oscillating AC current to a single-phase induction motor 410, such as the single-phase induction motor 300 of Figure 3.

Figure 5 shows circuitry 500 for resonant single-phase induction motor according to a first example teaching of the disclosure. Similar to the circuitry 400 of Figure 4, the circuitry 500 includes a single-phase AC power supply 522 that provides an AC current to a main winding 524 arranged to produce an oscillating magnetic field in response to an AC current, which drives rotation of a rotor 510 (such as a squirrel-cage rotor). The single-phase AC power supply 522 also provides an AC current to an auxiliary winding 526 arranged in parallel with the main winding 524. Arranged in series with the auxiliary winding 526 is a quadrature capacitor 523 in a similar manner to the circuitry 300 of Figure 3. The circuitry SOO may also include a switch 529 (such as a centrifugal switch) that is arranged to disconnect said branch from the power supply 522 once the rotor has reached a particular rotational speed, while leaving the branch including the main winding 524 connected to the power supply 522. Although the switch 529 is shown as a traditional flip switch, it may take the form of a transistor (or other) switch.

In addition, the circuitry 500 of Figure 5 includes a capacitor 525 (which may be referred to as a resonance capacitor) arranged in series with both branches of circuity 500 so as to be arranged in series with both the main winding 524 and the auxiliary winding 526. The combination of the resonance capacitor 525 and the main winding 524 has an electromagnetic resonant frequency in a similar manner to the capacitors 132 and windings 131 of the three-phase induction motor of Figure 1. The value of the electromagnetic resonant frequency is determined by the capacitance of the resonant capacitor 525 and the main winding 524. For example, the resonant capacitor may have a capacitance value of between 10 and 1000W.

When the AC current supplied by the single-phase AC power supply 522 is close to the resonant frequency, the output torque in the rotor 510 is greatly increased. By choosing the capacitance value of the resonant capacitor 525, the resonant electromagnetic frequency of the circuitry 500 can be set to a value close to the desired operating frequency of the motor 500 and as such greater output torque can be achieved close to a desired operating frequency. Accordingly, it is also possible to remove any ferromagnetic cores or laminations in the rotor 510 (for example to create an air-core rotor), as the additional magnetic coupling that these provide is not necessary in order to achieve a desired output torque. Consequently, the single-phase resonant induction motor 500 can be made smaller and more lightweight, as compared to traditional single-phase induction motors, without a reduction in output torque.

Moreover, the benefits of a resonant induction motor, including increased output torque and the ability to reduce the size and weight of the induction motor, can be realised in a single-phase motor, rather than being confined solely to three-phase induction motors, such as that in Figure 1.

Accordingly, the benefits of resonant induction motor can now be applied in less complex and cheaper induction motors. For example, according to the first example teaching of the disclosure, a resonant induction machine is provided that can be powered using a standard H-bridge circuit, rather than requiring a more complex three-phase inverter. In this way, the number of switches required to power the resonant induction machine can be reduced. Furthermore, while a three-phase resonant induction motor requires at least three (and sometimes six if capacitors are connected in the rotor circuit) capacitors, the single-phase resonant induction motor 500 of the present example requires only two. This reduction in the number of switches and capacitors results in a cheaper and smaller induction motor. Accordingly, it is possible to use resonant induction motors in lower cost implementations. For example, such a resonant induction motor can be employed in household fans, washing machines, household pumps, industrial low-power pumps, and low-power machining equipment.

Therefore, from one perspective there has been described an electrical machine, a stator for an electrical machine, and driving circuitry for a stator of an electrical machine. The driving circuitry includes a first winding and a first capacitor arranged in series with one another and arrange in parallel with a second winding. The driving circuitry further includes a second capacitor arranged in series with both the first and second windings. The driving circuitry is compatible with a single-phase AC power supply to generate increased output torque at a particular driving frequency.

Claims

Claims 1. Driving circuity for a stator for an electrical machine, the driving circuitry comprising: a first winding; a first capacitor arranged in series with the first winding a second winding arranged in parallel with the first winding and the first capacitor; and a second capacitor arranged in series with: the first winding and the first capacitor, and the second winding.
2. The driving circuitry according to any preceding claim, wherein a capacitance of the second capacitor and an inductance of the second winding are selected such that combination of the second capacitor and the second winding have an electromagnetic resonant frequency.
3. The driving circuitry according to claim 1 or claim 2, wherein the driving circuitry is configured to be electrically connected to a single-phase power supply.
4. The driving circuitry according to claim 3, further comprising the single-phase power supply.
5. The driving circuitry according to any of claims 1-4, wherein: the first winding and the first capacitor are arranged in series in a first branch of the driving circuity; the second winding is arranged on a second branch of the driving circuitry; wherein the first branch and the second branch are arranged in parallel with one another, and wherein the second capacitor is arranged in series with the first branch and the second branch.
6. The driving circuity according to claim 5, wherein the first branch further includes a switch arranged to switchably couple the first branch to a single-phase power supply.
7. The driving circuity according to claim 6, wherein the switch is a centrifugal switch configured to decouple the first branch from the single-phase power supply based on a rotational speed of a rotor of the electrical machine.
8. The driving circuitry according to any preceding claim, wherein a capacitance of the second capacitor is between 10microF and 1000microF.
9. A stator for an electrical machine comprising the driving circuitry according to any preceding claim.
10. An electrical machine comprising: the stator according to claim 9; and a rotor.
11. The electrical machine according to claim 10, wherein the rotor is a squirrel-cage rotor.
12. The electrical machine according to claim 10 or claim 11, wherein the rotor is an air-core rotor.
13. The electrical machine according to claim 10 or claim 11, wherein the rotor includes a core formed of a magnetic material.