FILTER FOR SUPPRESSING ELECTRIC CIRCULATION IN ROTATING ELECTRIC MACHINES

Abstract

A three-phase alternating current (AC) synchronous machine includes a stator with multiple stator slots, multiple stator windings arranged in a delta configuration and accommodated within the stator slots, and a common-mode filter contained within the stator, with filter windings of the common-mode filter wound circumferentially around a magnetic core of the common-mode filter and connected in series with the stator windings.

Description

TECHNICAL FIELDThe present application relates to rotating electric machines, and more particularly to three-phase AC synchronous machines, including wound rotor synchronous machines and permanent magnet synchronous machines.BACKGROUNDRotating electric machines, sometimes also referred to as electric motors, generally include a stator having multiple electrical windings and a rotor that can be angularly displaced relative to the stator in response to electrical current flowing through the windings. The rotating electrical machines may be present in any of a variety of different implementations. For example, the rotating electric machines may be implemented as a three-phase permanent magnet synchronous machine. This rotary electric machine implementation may be electrically coupled to a power source in various ways. That is, the windings of the rotating electric machine may be coupled to the power source via a star or delta connection. Depending on the connection, there may be a number of challenges regarding the presence of a circulating current in the windings.SUMMARYIn one implementation, a three-phase alternating current (AC) synchronous machine includes a stator having a plurality of stator slots, a plurality of stator windings arranged in a delta configuration and received within the stator slots, and a common mode filter included in the stator, wherein filter windings from the common mode filter are circumferentially wound around a magnetic core of the common mode filter and are connected in series with the stator windings.In another implementation, a three-phase AC synchronous machine includes a stator having a plurality of stator slots and a back yoke portion disposed axially outward of the plurality of stator slots; a plurality of stator windings arranged in a delta configuration and received within the stator slots; and a common mode filter having a magnetic core positioned adjacent an outer surface of the stator, wherein filter windings from the common mode filter are circumferentially wound around the magnetic core and are connected in series with the plurality of stator windings.In another implementation, a three-phase AC synchronous machine includes a stator having a plurality of stator slots and a back yoke portion disposed radially outward of the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received within the stator slots; and a common mode filter having a magnetic core positioned in the stator, wherein filter windings from the common mode filter are wound around the stator and connected in series with the plurality of stator windings.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a block diagram showing an implementation of an electrical system in which a three-phase AC synchronous machine is included; FIG. 2 is a perspective view showing an implementation of a common mode filter; FIG. 3 is a perspective view showing another implementation of a common mode filter; FIG. 4 is a perspective view showing another implementation of a common mode filter; FIGS. 5 a- 5 bare diagrams showing current performance of a three-phase AC synchronous machine with and without common mode filters; and FIGS. 6 a- 6 bare diagrams showing torque performance of a three-phase AC synchronous machine with and without common mode filters.DETAILED DESCRIPTIONA rotating electric machine or an electric motor may have windings electrically coupled to a power source and an inverter via a delta connection instead of via a star connection. Using the delta circuit instead of the star circuit in the rotating electric machine may entail the presence of a circulating current in the winding because the delta circuit forms a closed loop for harmonic voltage and current. While three-phase AC synchronous machine implementations of rotating electrical machines typically use star-connected windings, in certain implementations of three-phase AC synchronous machines, a particular input voltage or current, winding turn value, and / or economic reason may account for the preference of the delta connection. For example, electric motors with a relatively high rated power and / or with a specific input voltage / current can benefit from the delta connection. The delta connection may also help optimize the number of turns for hairpin or S-windings. However, the delta circuit may include a circulating current of voltage harmonics that may result in torque ripple, reduced output torque, and / or reduced efficiency.The dominant harmonic voltages in permanent magnet wound rotor synchronous machines are third harmonics and multiples of the third harmonics. The third harmonic voltages of three-phase stator windings may be in the same phase and magnitude. These harmonic voltages may cancel each other out to be net zero when the stator windings are configured as a star connection. However, in stator windings configured in a delta connection, the harmonic voltages may add up, resulting in an undesired circulating current within the windings.The circulating current in the delta connection can be reduced or eliminated using a common mode filter electrically connected to the stator windings arranged in a delta connection. The common mode filter may be implemented in various ways, but the stator windings may be electrically connected to filter windings wound around a magnetic core of the common mode filter such that the windings are wound around the filter and connected in series. The common mode filter includes the magnetic core and filter windings wound around the magnetic core. The number of turns around the common mode filter for each winding may vary and depend on the application. The third harmonic circulation current has the same magnitude and phase, thus is a common mode current. The three-phase harmonic base current is present at different phase angles, so that the sum of these currents is equal to zero. The common mode filter has, on account of its zero sum value, a low to no magnetic inductance at all for the fundamental harmonic of the three-phase current, but has a very high inductance for the common mode current. The common mode filter does not affect the fundamental harmonic of the three-phase current and suppresses the circulating current. An implementation of a rotary electric machine with common mode filters and stator windings in delta connection is described below with reference to an application in a battery powered electric vehicle (BEV); however, it is understood that other implementations are also possible.Referring to FIG. 1, an implementation of an electrical system 10 is shown that includes a power grid 12 and an electric vehicle (EV) 14 that can either receive electrical power from the grid 12 or supply electrical power to the latter. The power grid 12 may include any of a number of power generators and power supply mechanisms. Electrical generators (not shown) generate AC electrical power which can then be transmitted a substantial distance from the electrical generator for private and commercial use. The electric generator may be coupled to the power grid 12 that transfers the AC electric power from the electric generator to an end user, such as a home or enterprise. Because the AC electric power is supplied to the power grid 12, the electric power may be at a relatively high voltage so that it can be transmitted over relatively long distances. Once the electrical power reaches a location where it is to be used, electrical transformers (not shown) may be used to lower the level of the voltage before it is ultimately supplied to a home or enterprise. In one implementation, the voltage level of the AC electrical power used is 360-510 volts RMS AC three phase, 50-60 Hz. However, this voltage range may be different.The EV 14 may include an electric motor 16 that drives the vehicle in whole or at least in part. In the described implementation, the electric motor 16 may be a three-phase alternating current (AC) synchronous machine, but other implementations are also possible using the control and functionality described herein. The rotor may be a permanent magnet rotor or a wound rotor. Generally, the electric motor 16 may have a rated voltage of more than 200 V. The electric motor 16 may be, for example, a high voltage hairpin (HVH) electric motor having a rated voltage of 800 V and a power of 245 to 400 kW. The electric motor 16 includes a stator having slots that receive stator windings and a rotor that is angularly displaced relative to the stator in response to current flow through the stator windings. A three-phase inverter 18 may be electrically coupled to an EV battery 20 and the electric motor 16. The inverter 18 may receive DC electric power from the EV battery 20 and convert the DC electric power to three-phase AC electric power before the AC electric power is supplied to the electric motor 16. The voltage level supplied by the EV battery to the electric motor may vary depending on the application. The term "electric vehicle" or "EV" may refer to vehicles that are powered in whole or in part by electric motors. EV may refer to electric vehicles, plug-in electric vehicles, hybrid electric vehicles, and battery-powered vehicles.An EV charging station, referred to herein as a DC quick charger 22, may receive AC electrical power from the grid 12, rectify the AC electrical voltage to DC electrical power, and provide the DC electrical power to the EV 14. The DC fast charging device 22 may be geographically fixed, such as a charging station located in a vehicle garage or in a vehicle parking space. The DC fast charger 22 may include an input port that receives the AC electrical power from the grid 12 and passes the AC electrical power directly to the EV battery 20 bypassing an on-board battery charger 24 included on the EV 14. An electrical cable 26 may be removably connected to a power outlet on the EV 14 and electrically couple the DC quick charger 22 to the EV 14 so that DC electrical power may be transferred between the DC quick charger 22 and the EV battery 20. One type of DC fast charge may be referred to as EV charge level 3, which is considered 60-350 kW. However, other charging standards are also possible with the structure and functionality described herein. The EV battery 20 may supply the electric motor 16 that drives the EV 14 with DC electric power controlled by power electronics. The EV battery 20 or batteries are rechargeable. Examples of batteries include lead-acid batteries, nickel-cadmium (NiCd), nickel-metal hydride, lithium-ion, and lithium-polymer batteries. However, battery technology continues to develop and other chemicals and / or voltages may also be used. A typical range of vehicle battery voltages may range from 100 to 1000 V of DC electric power (VDC).Turning to FIG. 2, a general schematic illustration of a common mode filter 30 is shown having a magnetic core 30 aand three filter windings 30 bconnected in series with the three-phase stator windings (U, V, W) included in the electric motor 16. The common mode filter includes the magnetic core 30 aand the filter windings 30 bwinded around the magnetic core 30 a. The filter windings 30 bmay include three separate windings wound in the same direction as the stator windings (U, V, W), and each of the three filter windings 30 bmay be individually connected to a phase of the windings. The magnetic core 30 amay be an iron loop around which the filter windings 30 bare wound. However, the magnetic core 30 amay be formed of any of various materials such as powder core, ferrite, iron lamination, or another soft magnetic material. The three-phase stator windings are arranged in a delta connection and not in a star connection electrically in the stator of the electric motor 16. The delta circuit includes three individual stator windings (U, V, W) electrically connected to each other in a loop, and does not have a neutral conductor unlike the star circuit. The delta arrangement may result in a circulating current that includes third harmonic currents in each of the stator windings (U, V, W). In contrast, in a star configuration, the vectors of the third harmonic voltage are equal in each phase of the stator windings and cancel each other out, so that there is no circulating current due to the presence of the third harmonic. However, in the delta connection, the vectors of the third harmonic voltage may add up in the formed delta loop so that a circulating current exists. The number of windings and the strength of the windings may vary depending on the implementation.FIG. 3 shows a partial view of another implementation of a common mode filter 31 as coupled to a stator 32 aof the electric motor 16. This is a pole section of a multipolar motor. The common mode filter 31 includes a magnetic core 31 aand the filter windings 31 bwinded around the magnetic core 31 a. The stator 32 aincludes stator slots 36 that accommodate three stator windings (U, V, W). The magnetic core 31 ais shown as a single unitary structure having a length of three filter windings 31 bextending from a radially extending surface 34 of the stator 32 aand wound around an outer periphery of the common mode filter core 31 a. The filter windings 31 bmay each be connected in series with one of the stator windings (U, V, W). A length of the filter windings 31 belectrically connected to the U stator winding may wind around the magnetic core 31 aover a circumferential length (L), a length of the filter windings 31 belectrically connected to the V stator winding may wind around the magnetic core 31 aover an adjacent circumferential length of the common mode filter 31, and a length of the filter windings 31 belectrically connected to the W stator winding may wind around the magnetic core 31 aover a circumferential length of the common mode filter 31 besides the length of the V winding. The filter winding arrangement is flexible as long as the filter windings have equal numbers of turns for each phase. In this implementation, the common mode filter 31 may be fixed as a unitary member having a relatively circular cross-sectional shape to a radially extending surface 34 of the stator 32 a. However, it should be noted that other implementations are also possible in which different cross-sectional shapes are chosen, or a plurality of common mode filters may be attached to the stator.FIG. 4 shows a partial view of an implementation of a common mode filter 33 which is integrated in a return section 38 of the stator 32 b. This is a pole section of a multipolar motor. The stator 32b includes a plurality of stator slots 36, a return portion 38 and a plurality of apertures 39 at the junction of stator teeth and stator return for receiving filter wires. The common mode filter 33 uses the back yoke portion 38 as a magnetic core and includes filter wires 33 b. A plurality of grooves 40 may be formed on the back yoke portion 38 and extend axially in a direction substantially parallel to the slots 36. Three filter windings 33 bmay be wound around the return portion 38 of the stator 32 b, extend through the openings 39 and fit into the slots 40. A length of the filter windings 31 bis wound around the return portion 38 and is connected to the U stator winding over a circumferential length (L), a length of the filter windings 33 bis wound around the return portion 38 and is connected to the V stator winding over a circumferential length (L), and a length of the filter windings 33 bis wound around the return portion 38 and is connected to the W stator winding over a circumferential length (L).FIGS. 5-6 show analysis results of motor operation with and without common mode filter 30, FIG. 5a is a plot of the simulated current in the stator windings (U, V, W) of motor 16 without common mode filter 30 over time, while FIG. 5b is a plot of the simulated current in the stator windings (U, V, W) of motor 16 with common mode filter 30 over time. FIG. 6 ais a plot of the simulated torque of the electric motor 16 without the common mode filter 30 over time, while FIG. 6 bis a plot of the simulated torque of the electric motor 16 with the common mode filter 30 over time. Prior to applying the common mode filter 30, the electric motor 16 outputs an average torque of 1084 Nm (337 Nm peak-to-peak ripple) and high third harmonics in the phase current. After applying the common mode filter 30, the electric motor 16 outputs an average torque of 1148 Nm (135 Nm peak-to-peak ripple) and lower harmonics in the phase current. Inclusion of the common mode filter 30 may result in a 20% reduction in copper losses, a 6% increase in torque output, and a more than 60% reduction in peak-to-peak torque ripple.It should be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but is defined solely by the following claims. Moreover, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of the terms used in the claims, unless a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes and modifications are intended to fall within the scope of the appended claims.As used in this specification and the claims, the terms "e.g.," "for example," "for example," "such as," and "like," and the verbs "comprise," "have," "have / include," and their other verb forms, when used in connection with a enumeration of one or more components or other elements, are each intended to be open ended, meaning that the enumeration is not intended to be viewed as excluding other or additional components or elements. Other terms are to be interpreted in their broadest acceptable meaning unless used in a context that requires a different interpretation.Although the present invention has been described above and is defined in the appended claims, it is to be understood that the invention may alternatively be defined according to the following embodiments: 1. a three phase alternating current (AC) synchronous machine comprising:a stator having a plurality of stator slots;a plurality of stator windings arranged in a delta configuration and received within the stator slots; anda common mode filter included in the stator, wherein filter windings of the common mode filter are circumferentially wound around a magnetic core of the common mode filter and connected in series with the stator windings.2. The three-phase AC synchronous machine according to Embodiment 1, further comprising an electric vehicle (EV) operatively coupled to the three-phase AC synchronous machine. 3. the three-phase AC synchronous machine according to Embodiment 1, wherein the magnetic core of the common mode filter is a single unitary structure. 4. the three-phase AC synchronous machine according to Embodiment 1, wherein the magnetic core of the common mode filter has a circular or rectangular cross-sectional shape. 5. a three-phase alternating current (AC) synchronous machine comprising:a stator having a plurality of stator slots and a flux return portion positioned axially outside the plurality of stator slots;a plurality of stator windings arranged in a delta configuration and received within the stator slots; anda common mode filter comprising a magnetic core positioned adjacent an outer surface of the stator, wherein filter windings from the common mode filter are circumferentially wound around the magnetic core and are connected in series with the plurality of stator windings.6. The three-phase AC synchronous machine according to Embodiment 5, further comprising an electric vehicle (EV) operatively coupled to the three-phase alternating current (AC) synchronous machine. 7. the three-phase AC synchronous machine according to Embodiment 5, wherein the magnetic core of the common mode filter is a single unitary structure. 8. the three-phase AC synchronous machine according to Embodiment 5, wherein the magnetic core of the common mode filter is coupled to a radially extending surface of the stator. 9. the three-phase AC synchronous machine according to Embodiment 5, wherein the magnetic core of the common mode filter has a circular or rectangular cross-sectional shape. 10 The three-phase AC synchronous machine according to Embodiment 5, wherein the magnetic core of the common mode filter is ring-shaped. 11.A three-phase alternating current (AC) synchronous machine comprising:a stator having a plurality of stator slots and a flux return portion positioned radially outward of the plurality of stator slots;a plurality of stator windings arranged in a delta configuration and received within the stator slots; anda common mode filter having a magnetic core integrated in the stator, wherein filter windings of the common mode filter are wound around the stator and connected in series with the plurality of stator windings.12. The three-phase AC synchronous machine according to Embodiment 11, further comprising an electric vehicle (EV) operatively coupled to the three-phase alternating current (AC) synchronous machine. 13.The three-phase AC synchronous machine of Embodiment 11, further comprising a plurality of slots and apertures formed in the stator and shaped to receive filter windings wound on the stator. 14. three-phase AC synchronous machine according to Embodiment 11, wherein the filter windings are wound around the back yoke portion of the stator.

Claims

A three-phase alternating current (AC) synchronous machine comprising: a stator having a plurality of stator slots; a plurality of stator windings arranged in a delta connection and accommodated within the stator slots; and a common mode filter included in the stator, wherein filter windings of the common mode filter are circumferentially wound around a magnetic core of the common mode filter and are connected in series with the stator windings.The three-phase AC synchronous machine according to claim 1, wherein the magnetic core of the common mode filter is a single unitary structure.The three-phase alternating current synchronous machine according to any one of the preceding claims, wherein the magnetic core of the common mode filter has a circular or rectangular cross-sectional shape.An electric vehicle (EV) comprising the three-phase AC synchronous machine according to any of the preceding claims, wherein the electric vehicle (EV) is operatively coupled to the three-phase AC synchronous machine.A three phase alternating current (AC) synchronous machine comprising: a stator having a plurality of stator slots and a back yoke portion positioned axially outward of the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received within the stator slots; and a common mode filter having a magnetic core positioned adjacent an outer surface of the stator, wherein filter windings from the common mode filter are circumferentially wound around the magnetic core and are connected in series with the plurality of stator windings.The three-phase AC synchronous machine according to claim 5, wherein the magnetic core of the common mode filter is a single unitary structure.The three-phase AC synchronous machine of any of claims 5 or 6, wherein the magnetic core of the common mode filter is coupled to a radially extending surface of the stator.The three-phase AC synchronous machine according to any one of claims 5 to 7, wherein the magnetic core of the common mode filter has a circular or rectangular cross-sectional shape.The three-phase AC synchronous machine according to any one of claims 5 to 8, wherein the magnetic core of the common mode filter is ring-shaped.An electric vehicle (EV) comprising the three-phase AC synchronous machine according to any one of claims 5 to 9, wherein the electric vehicle (EV) is operatively coupled to the three-phase AC synchronous machine.A three phase alternating current (AC) synchronous machine comprising: a stator having a plurality of stator slots and a back yoke portion positioned radially outward of the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received within the stator slots; and a common mode filter having a magnetic core integrated within the stator, wherein filter windings from the common mode filter are wound around the stator and are connected in series with the plurality of stator windings.The three-phase AC synchronous machine of claim 11, further comprising a plurality of slots and apertures formed in the stator and shaped to receive filter windings wound on the stator.The three-phase AC synchronous machine of any of claims 11 or 12, wherein the filter windings are wound around the back yoke portion of the stator.An electric vehicle (EV) comprising the three-phase AC synchronous machine according to any one of claims 11 to 13, wherein the electric vehicle (EV) is operatively coupled to the three-phase AC synchronous machine.

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