GB2622587A

GB2622587A - Resonant electrical machine

Info

Publication number: GB2622587A
Application number: GB2213727.7A
Authority: GB
Inventors: Abduallah Ahmad; Komi Yoshiyuki; Umemura Chiaki
Original assignee: IMRA Europe SAS
Current assignee: IMRA Europe SAS
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2024-03-27
Also published as: GB202213727D0

Abstract

An electrical induction motor, for example a parallel resonance induction motor 300, has a stator 330 including windings 331 arranged in series with capacitors 332. A further set of windings 333 is arranged in parallel with the capacitors. The parallel resonance induction machine may include switches 340a-c which selectively disconnect the windings from a power source of the stator. Accordingly, the parallel resonance induction machine may revert to operation as a traditional resonant electrical machine by opening the switches, and may operate as a parallel resonance induction machine by closing the switches. A controller may be provided to actuate the switches at one or more predetermined operating frequencies of the electrical power supply. A controller may be configured to control a driving frequency of the electrical power supply to prevent the driving frequency being within a predetermined frequency range.

Description

RESONANT ELECTRICAL MACHINE

Field of the Invention

The invention relates generally to electrical machines and driving circuitry for electrical machines, more specifically electrical machines with an electromagnetic resonant frequency.

Background

Many modern electrical motors are three-phase electrical motors. In a three-phase electrical motor, a driving voltage of three phases is provided to windings of a stator. The provision of a three-phase driving voltage in this manner creates a rotating magnetic field in which a rotor of the electrical motor is made to rotate, thus generating mechanical power.

More recently, so-called resonant electrical motors have been developed, which are a type of three-phase electrical motor. In a resonant electrical motor, a capacitor is arranged in series with each of the stator windings. The stator windings and the capacitors arranged in series form part of an electromagnetically resonant circuit having a resonant frequency determined by the inductance values of the windings and the capacitance values of the capacitors.

Resonant electrical motors can generate comparatively large power outputs, however the maximum output power of the electrical motor can only be obtained at a very narrow three-phase driving voltage frequency, close to the resonant frequency of the driving circuit of the stator. Therefore, resonant electrical motors of this type produce only a small amount of power at low driving voltage frequencies.

The present inventors have identified an improved resonant electrical motor that provides increased maximum power output at low driving frequencies.

Summary of the Invention

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

According to a first aspect of the invention, there is provided driving circuitry for a stator for an electrical induction motor, the driving circuitry comprising: a first set of windings configured to produce a magnetic field when electrically connected to an electrical power supply; one or more capacitors arranged in series with each winding of the first set of windings; and a second set of windings each arranged in parallel with a respective one of the one or more capacitors.

Accordingly, it is possible to provide an induction motor which can produce comparatively high output current torques, particularly at low frequencies.

In some examples, the one or more capacitors and a respective winding of the second set of windings are arranged in a first circuit branch, wherein the first circuit branch is arranged in series with a respective winding of the first set of windings. In some examples, the first set of windings include three windings configured to produce a rotating magnetic field when connected to a three power supply; wherein the one or more capacitors include three capacitors each arranged in series with a respective one of the first set of windings; and wherein the second set of windings include three windings each arranged in parallel with a respective one of the capacitors.

In some examples, the driving circuitry further comprises: one or more switches, the one or more switching devices arranged to selectively connect or disconnect the second set of windings from the power supply without disconnecting the one or more capacitors from the power supply. As such, the output of the induction motor can be maximised across a range of driving frequencies.

In this example, the driving circuitry may further comprise: a controller, wherein the controller is configured to actuate the one or more switching devices at one or more predetermined operating frequencies of the electrical power supply. Accordingly, the frequency at which the switches actuate may be optimised, thereby maximising the output of the motor at a given driving frequency.

In some examples, the driving circuitry further comprises: a controller configured to control a driving frequency of the electrical power supply. The controller of this example may be the same controller as a controller that configured to actuate the one or more switching devices at one or more predetermined operating frequencies of the electrical power supply, or the controller of this example may be a different controller. In this way, it is possible to operate the induction motor at a range of frequencies, thus providing flexibility in the operation of the motor.

In this example, the controller may be configured to cause change the driving frequency of the electrical power supply to prevent the driving frequency being within a predetermined frequency range. Therefore, driving frequency may be controlled to avoid ranges of frequencies where the output of the induction motor may be comparatively low.

In this example, the predetermined frequency range may extend from a first driving frequency to a second driving frequency, wherein the controller is configured to cause a step change in the driving frequency from a first driving frequency to a second driving frequency, to avoid the predetermined frequency range. In these examples, the controller may be configured to change a slip frequency of the electrical machine.

In some examples, the driving circuitry may further comprise the electrical power supply. Advantageously, the driving circuitry has an electromagnetic resonant frequency. Accordingly, the induction motor may produce significantly increased outputs at particular frequency values or ranges.

According to a second aspect, there is provided a stator for an electrical induction motor, the stator comprising the driving circuitry as described above, According to a third aspect of the invention, there is provided an electrical induction motor, the electrical induction motor comprising: a stator as described above; and a rotor comprising one or more rotor windings, wherein the rotor is configured to rotate in response to a magnetic field produced by the stator.

In some examples, the electrical induction motor comprises a core formed of a non-magnetic material. In some examples, the rotor is a coreless rotor. As such, the induction motors described herein may be made lightweight and compact, without significantly reducing the output of the induction motor. In some examples, the electrical induction motor comprises a core formed of a ferromagnetic material. As such, the output torque of the motor at low frequencies may be significantly increased.

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 depicts an example of a traditional resonant electrical machine; Figure 2 is a graph showing comparative stator current values for a traditional electrical induction motor and a resonant electrical induction motor.

Figure 3 illustrates an examples of a parallel resonance induction motor according to an

example of the present disclosure.

Figure 4 is a graph showing comparative stator current values for a traditional electrical induction motor, a resonant electrical induction motor, and a parallel resonance induction motor.

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 an example traditional resonant electrical machine 100 and a representation of the circuitry for the electrical machine 100. The electrical machine 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 electrical machine 100 of Figure 1 also 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.

Rotor 110 also includes a plurality of capacitors 112 arranged in series with the rotor windings 111. Capacitor 112a is arranged in series with rotor winding 111a, capacitor 112b is arranged in series with rotor winding 111b, and capacitor 112c is arranged in series with rotor winding 111c. The inductances of the rotor windings 111a-111c are equal (or approximately equal) to one another, and the capacitances of the capacitors 112a-112c are equal (or approximately equal) to one another.

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. Similarly, the combination of the rotor windings 111 and the capacitors 112 has 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 and the resonant frequency of the rotor are set to be approximately equal to one another. In some examples, the stator 110 may not include capacitors 112. That is, the electrical machine 100 may function as a resonant electrical machine with only capacitors 132 being included in the circuitry, i.e. without capacitors 112.

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. As such, resonant electrical machines can be made lighter (e.g. by removing the iron core provided in most non-resonant electrical machines) and smaller. However, when the driving frequency is not close to the resonant frequencies, the output torque of the electrical machine 100 is significantly lower. As such, the overall range of driving frequencies at which the resonant electrical machine 100 can be operated with adequate output torque is small.

This effect is particularly pronounced at driving frequencies close to zero. Figure 2 is a graph showing comparative stator current values As for a traditional (ferromagnetic core) electrical induction motor 210, and a resonant electrical induction motor 220 such as that discussed above in relation to Figure 1, for a range of driving frequencies f. As can be seen, at a driving frequency close to zero, the resonant electrical induction motor 220 produces only a small amount of stator current, and therefore only a small amount of torque. In comparison, the traditional electrical induction motor 210 produces a significant level of current at low frequencies, which slowly decreases with increasing frequency. It is therefore desirable to provide an electrical machine which provides the benefits of a resonant electrical machine 220 in allowing large output currents/torques to be produced by a lightweight and compact motor, but which also provides large output currents/torques at low driving frequencies, as with traditional electrical induction motor 210.

Figure 3 shows an example of a parallel resonance induction motor 300 according to an example of the present disclosure. The rotor 310 may be substantially similar to rotor 110 of Figure 1, and may include windings 311 similar to windings 111 of Figure 1, however the presence of capacitors 112 may not be necessary. The parallel resonance induction motor 300 also includes a stator 330 arranged with the rotor 310 to have an air gap 320 therebetween. The stator 330 includes windings 331 which may be similar to windings 121 of Figure 1.

The stator 330 additionally includes capacitors 332. A further set of windings 333 is arranged in parallel with the capacitors 332. That is, winding 333a is arranged in parallel with capacitor 332a, winding 333h is arranged in parallel with capacitor 332b, and winding 333c is arranged in parallel with capacitor 332c. As such, respective circuit branches 350a-c including capacitors 332a-c and windings 333a-c are arranged in series with respective windings 331a-c.

In some examples, the parallel resonance induction machine 300 may include switches 340a-c which selectively disconnect the windings 333 from a power source of the stator 330. Accordingly, the parallel resonance induction machine 300 may revert to operation as a traditional resonant electrical machine by opening the switches 340, and may operate as a parallel resonance induction machine by closing the switches 340.

Figure 4 is a graph showing comparative peak stator currents A, for a range of driving frequencies f for a conventional electrical induction motor 410, a resonant electrical induction motor 420, and a parallel resonance induction motor 430. As can be seen, at low driving frequencies (i.e. from fo to fi) the stator current of the parallel resonance induction motor 430 is comparable to that of a traditional non-resonant induction motor 410 (including a ferromagnetic core), and significantly above that of a resonant electrical induction motor 420.

After the peak current at f1, as the driving frequency increases the stator current of the parallel resonance induction motor 430 decreases and becomes lower than that of the resonant induction motor 420 at f2, but remains close to the output of the conventional electrical induction motor 410. The current of the resonant electrical induction motor 420 peaks at f3.

The current of the parallel resonance induction machine 430 continues to decrease faster than the traditional non-resonant induction motor 410 and becomes approximately zero at frequency fa. This phenomenon occurs as in the frequency region of fa the impedance of the circuit is comparatively, causing current to circulate within the circuit branches 350a-c, as will be explained later.

After frequency fa, the stator current of the parallel resonance induction motor 430 increases once again, peaking at f5, where the stator current of the parallel resonance induction motor 430 is larger than both the conventional electrical induction motor 410 and the resonant induction motor 420. After f5, the stator current of the parallel resonance induction motor 430 decreases and becomes similar to that of the conventional electrical induction motor 410 and the resonant induction motor 420.

The behaviour of the stator current between f3 and f5, can be understood with reference to the electrical reactance and impedance of the circuitry. In particular, impedance of the circuitry is based on both capacitive and inductive reactance of the circuitry. Capacitive reactance X, is given by the following equation:

X -

c 27if C where f is the driving frequency, and C is capacitance. Inductive reactance XL is given by the following equation: XL = DrfL where L is inductance. Accordingly, it can be seen that when the driving frequency is low, the capacitive reactance is high, while the inductive reactance is low. Conversely, when the driving frequency is high, the capacitive reactance is low, while the inductive reactance is high.

Therefore, at low driving frequencies the impedance of the windings 333 is comparatively low, while the impedance of the capacitors 332 is comparatively high, and as such the behaviour of the electrical parallel resonance induction motor 300, 430 is determined primarily by the properties of the windings 333, rather than the capacitors 332. Accordingly, the parallel resonance induction motor 430 behaves similarly to the traditional non-resonant induction motor 410. Conversely, at high frequencies the impedance of the windings 333 is comparatively high, while the impedance of the capacitors 332 is comparatively low, and as such the behaviour of the electrical parallel resonance induction motor 300, 430 is determined primarily by the properties of the capacitors 332, rather than the windings 333. Accordingly, the parallel resonance induction motor 430 behaves similarly to the resonant induction motor 420.

At frequency f4, the impedance of both the capacitors 332 and the windings 333 is equal. At this point, the impedance of the remainder of the circuit is high in comparison to the impedance of the circuit branches 350. Accordingly, due to this comparatively high external impedance the current circulates entirely or almost entirely within the circuit branches 350. In the neighbouring frequencies close to f4, current circulation within the branches 350 occurs however the amount of current circulation is smaller, leading to non-zero stator current values.

There are a number of possible mechanisms to avoid the significant decrease in stator current produced by the parallel resonance induction motor 300, 430 in the vicinity of f4. For example, a controller may be provided which controls the driving frequency for the stator 330. When setting the driving frequency, the controller may skip the frequency region in the vicinity of to f4. In other words, at a first predetermined driving frequency, the controller may be configured to cause a step change in the driving frequency to a second predetermined frequency, where fa is between the first and second predetermined frequencies. In this way, the frequency region of zero or near-zero stator current may be avoided. In a similar manner, the controller may alternatively alter a slip frequency of the electrical machine to avoid the region wherein the output current falls to near zero.

As an alternative measure, the parallel resonance induction motor 300, 430 may be provided with switches 340a-c described above. In this way, the windings 333 may be selectively disconnected from the power source. Accordingly, a controller may be configured to control the switches to be closed below a predetermined frequency, such as frequency f2, and to be open above the predetermined frequency. As such, below the predetermined frequency, the stator current of the parallel resonance induction motor may follow the curve 430 shown in Figure 4, while above the predetermined frequency, the stator current of the parallel resonance induction motor may follow the curve 420 for the resonant induction motor 420 shown in Figure 4. In this way, as the windings 333 are disconnected from the power source at frequency of fa, the stator current does not reduce to zero or near-zero as discussed above. In some examples, the controller may additionally close the switches at frequency f5 or a frequency between fa and fs in order to take advantage of the fact that the stator current of the parallel resonance induction motor 430 includes an additional peak at f5. Accordingly, the stator current of the parallel resonance induction motor may be maximised across the entire possible frequency range, while including a comparatively high value of stator current at low driving frequencies.

Therefore, according to the above examples and techniques it is possible to provide an electrical induction motor which can produce comparatively high output current torques, particularly at low frequencies, without requiring a ferromagnetic core. That is, the parallel resonance induction motor may be provided with a non-magnetic core, or may be a so-called careless or air-core induction motor. Therefore, the motor may be made lightweight and compact, without significant reduction in the motor output at low frequencies. However, in some examples, the parallel resonance induction motor may include a ferromagnetic core, and as such the output torque of the motor at low frequencies may be significantly increased.

Induction motors of the type described herein may be used for a variety of applications, such as motor vehicles, electric bicycles or scooters and many more.

There has therefore been described driving circuitry for a stator of an electrical induction motor wherein a resonant electrical machine is provided with a coil in parallel with the resonance capacitors. The driving circuitry includes a first set of coils is configured to produce a magnetic field when electrically connected to an electrical power supply; one or more capacitors arranged in series with each coil of the first set of coils; and a second set of coils each arranged in parallel with a respective one of the one or more capacitors.

Claims

CLAIMS1. Driving circuitry for a stator for an electrical induction motor, the driving circuitry comprising: a first set of windings configured to produce a magnetic field when electrically connected to an electrical power supply; one or more capacitors arranged in series with each winding of the first set of windings; and a second set of windings each arranged in parallel with a respective one of the one or more capacitors.
2. The driving circuitry according to claim 1, wherein the one or more capacitors and a respective winding of the second set of windings are arranged in a first circuit branch, wherein the first circuit branch is arranged in series with a respective winding of the first set of windings.
3. The driving circuitry according to claim 1 or claim 2, wherein the first set of windings include three windings configured to produce a rotating magnetic field when connected to a three power supply; wherein the one or more capacitors include three capacitors each arranged in series with a respective one of the first set of windings; and wherein the second set of windings include three windings each arranged in parallel with a respective one of the capacitors.
4. The driving circuitry according to any preceding claim, further comprising: one or more switches, the one or more switching devices arranged to selectively connect or disconnect the second set of windings from the power supply without disconnecting the one or more capacitors from the power supply.
The driving circuitry according to claim 4, further comprising: a controller, wherein the controller is configured to actuate the one or more switching devices at one or more predetermined operating frequencies of the electrical power supply.
6. The driving circuitry according to any preceding claim, further comprising: a controller configured to control a driving frequency of the electrical power supply.
7. The driving circuitry according to claim 6, wherein the controller is configured to cause change the driving frequency of the electrical power supply to prevent the driving frequency being within a predetermined frequency range.
8. The driving circuitry according to claim 7, wherein the predetermined frequency range extends from a first driving frequency to a second driving frequency, wherein the controller is configured to cause a step change in the driving frequency from a first driving frequency to a second driving frequency, to avoid the predetermined frequency range.
9. The driving circuitry according to any of claims 6-8, wherein the controller is configured to change a slip frequency of the electrical machine.
10. The driving circuitry according to any preceding claim, further comprising the electrical power supply.
11. The driving circuitry according to any preceding claim, wherein the driving circuitry has an electromagnetic resonant frequency.
12. A stator for an electrical induction motor, the stator comprising the driving circuitry according to any preceding claim,
13. An electrical induction motor, the electrical induction motor comprising: the stator according to claim 12; and a rotor comprising one or more rotor windings, wherein the rotor is configured to rotate in response to a magnetic field produced by the stator.
14. The electrical induction motor according to claim 13, wherein the electrical induction motor comprises a core formed of a non-magnetic material.
15. The electrical induction motor according to claim 13, wherein the rotor is a coreless rotor.
16. The electrical induction motor according to claim 12, wherein the electrical induction motor comprises a core formed of a ferromagnetic material.