Filter for suppressing circulating current in rotating electric machine

Abstract

A three-phase alternating current (AC) synchronous motor includes a stator having a 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 included with the stator wherein a filter winding from the common mode filter is circumferentially wound on a magnetic core of the common mode filter and connected in series to the stator winding.

Description

Technical Field

[0001] The present application relates to rotating electrical machines, and more particularly to three-phase AC synchronous machines, including wound rotor synchronous machines and permanent magnet synchronous machines. Background Art

[0002] A rotating electrical machine, sometimes referred to as an electric motor, typically includes a stator having a plurality of electrical windings and a rotor that can be angularly displaced relative to the stator in response to current flowing through the windings. A rotating electrical machine can exist in any of a variety of different implementations. For example, a rotating electrical machine can be implemented as a three-phase permanent magnet synchronous motor. A rotating electrical machine of such an implementation can be electrically coupled to a power source in a variety of different ways. That is, the windings of the rotating electrical machine can be coupled to a power source using a Wye connection (Y-type connection) or a Delta connection (Δ-type connection). Depending on the connection, there can be a number of challenges regarding the presence of circulating currents in the windings. Summary of the invention

[0003] In one implementation, a three-phase alternating current (AC) synchronous motor includes a stator having a plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; and a common mode filter included with the stator, wherein a filter winding from the common mode filter is circumferentially wound on a magnetic core of the common mode filter and connected in series to the stator windings.

[0004] In another embodiment, a three-phase AC synchronous motor includes a stator having a plurality of stator slots and a back iron region positioned axially outward from the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; and a common mode filter including a magnetic core positioned adjacent to an outer surface of the stator, wherein a filter winding from the common mode filter is circumferentially wound on the magnetic core and connected in series to the plurality of stator windings.

[0005] In yet another embodiment, a three-phase AC synchronous motor includes a stator having a plurality of stator slots and a back iron region positioned radially outward from the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; and a common mode filter including a magnetic core integrated with the stator, wherein a filter winding from the common mode filter is wound on the stator and connected in series to the plurality of stator windings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a block diagram depicting an implementation of an electrical system including a three-phase AC synchronous motor;

[0007] Figure 2 is a perspective diagram depicting how a common mode filter is implemented;

[0008] Figure 3 is a perspective diagram depicting another implementation of a common mode filter;

[0009] Figure 4 is a perspective diagram depicting another implementation of a common mode filter;

[0010] 5a-5b are graphs depicting current performance of a three-phase AC synchronous motor with and without a common mode filter; and

[0011] 6a-6b are graphs depicting the torque performance of a three-phase AC synchronous motor with and without a common mode filter. DETAILED DESCRIPTION

[0012] A rotating electrical machine or motor may have windings that are electrically coupled to a power source and an inverter via a Delta connection rather than a Wye connection. Using a Delta connection rather than a Wye connection on a rotating electrical machine may involve the presence of circulating currents in the windings because the Delta connection forms a closed loop of harmonic voltages and currents. Although three-phase AC synchronous motor implementations of rotating electrical machines typically use windings with Wye connections, certain three-phase AC synchronous motor implementations may involve specific input voltages or currents, specified winding turns, and / or economic reasons that make Delta connections more desirable. For example, motors with relatively high power ratings and / or receiving specific input voltages / currents may benefit from Delta connections. Delta connections can also help optimize the number of turns of hairpin or S-wound stator windings. However, Delta connections may include circulating currents generated by voltage harmonics, which may result in torque ripples, reduced output torque, and / or reduced efficiency.

[0013] The main harmonic voltages in permanent magnet synchronous motors and wound rotor synchronous motors are the third harmonic and multiples of the third harmonic. The third harmonic voltages from the three-phase stator winding can exist with the same phase and amplitude. When the stator winding is configured as a Wye connection, these harmonic voltages can cancel each other and reach a net zero. However, stator windings configured in a Delta connection can cause the harmonic voltages to superimpose on each other, resulting in undesirable circulating currents within the windings.

[0014] A common mode filter can be used to reduce or eliminate circulating currents in a delta connection, the common mode filter being electrically connected to a stator winding arranged in a delta connection. The common mode filter can be implemented in a variety of different ways, but the stator winding can be electrically connected to a filter winding wound on a magnetic core of the common mode filter, so that the winding is wound on the filter and arranged in series. The common mode filter includes a magnetic core and a filter winding wound on the magnetic core. The number of turns of each winding around the common mode filter can vary depending on the application. The third harmonic circulating current has the same amplitude and phase, and is therefore a common mode current. The fundamental three-phase current exists at different phase angles, so that the sum of these currents is equal to zero. Since the sum of the fundamental waves of the three-phase current is zero, the common mode filter has almost no magnetic induction intensity to the fundamental wave of the three-phase current, but has a very high magnetic induction intensity to the common mode current. The common mode filter does not affect the fundamental three-phase current and will suppress the circulating current. In the following, an implementation of a rotating electrical machine with a common mode filter and delta-connected stator windings will be described with reference to an application in a battery electric vehicle (BEV), however, it should be clear that other implementations are possible.

[0015] come Figure 1 , an implementation of an electrical system 10 is shown, including a power grid 12 and an electric vehicle (EV) 14, which can receive power from the power grid 12 or provide power to the power grid 12. The power grid 12 may include any of a variety of generators and power transmission mechanisms. The generator (not shown) produces alternating current, which can then be transmitted to a place far away from the generator for residential and commercial purposes. The generator can be coupled to the power grid 12, and the power grid transmits the alternating current from the generator to an end user, such as a residence or a business. When the alternating current is provided to the power grid 12, the power can exist at a relatively high voltage, so that it can be transmitted over a relatively long distance. Once the power reaches the location where it is intended to be used, a transformer (not shown) can be used to reduce the voltage level and then ultimately provided to a residence or business. In one implementation, the voltage level of the alternating current used is 360-510 volts effective value (RMS) AC three-phase, 50-60hz. However, this voltage range can be different.

[0016] The EV 14 may include an electric motor 16 that fully or at least partially propels the vehicle. In the described implementation, the electric motor 16 may be a three-phase alternating current (AC) synchronous motor, but other implementations using the controller and functions described herein are possible. The rotor may be a permanent magnet rotor or a wound rotor. In general, the electric motor 16 may have a rated voltage greater than 200V. For example, the electric motor 16 may be a high voltage hairpin (HVH) motor having a rated voltage of 800V and a power of 245-400kW. The electric motor 16 includes a stator and a rotor, the stator having slots for receiving stator windings, and the rotor angularly displaced relative to the stator in response to current flowing through the stator windings. A three-phase power inverter 18 may be electrically coupled to the EV battery 20 and the electric motor 16. The power inverter may receive direct current from the EV battery 20, invert the direct current into three-phase alternating current, and then supply the alternating current to the electric motor 16. The amount of voltage supplied by the EV battery to the electric motor may vary depending on the application. The term "electric vehicle" or "EV" may refer to a vehicle that is fully or partially propelled by an electric motor. EV can refer to electric vehicles, plug-in electric vehicles, hybrid electric vehicles and battery-powered electric vehicles.

[0017] An EV charging station, referred to herein as a DC fast charger 22, can receive AC power from the grid 12, rectify the AC voltage to DC power, and provide the DC power to the EV 14. The DC fast charger 22 can be fixed in geographical location, such as a charging station located in a garage or in a parking lot. The DC fast charger 22 may include an input terminal that receives AC power from the grid 12 and transmits the AC power directly to the EV battery 20, bypassing an onboard vehicle battery charger 24 included on the EV 14. A cable 26 may be removably connected to an electrical outlet on the EV 14 and electrically links the DC fast charger 22 to the EV 14 so that DC power can be transmitted between the DC fast charger 22 and the EV battery 20. One type of DC fast charging may be referred to as Level 3 EV charging, which is considered to be 60-350kW. However, other charging standards and power levels are also possible based on the structure and functionality disclosed herein. The EV battery 20 may supply DC power controlled by power electronics to the electric motor 16 that propels the EV 14. The EV battery 20 or batteries are rechargeable. Examples of batteries include lead-acid batteries, nickel-cadmium (NiCd) batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-polymer batteries. However, battery technology is evolving and other chemistries and / or voltages may be used. Typical vehicle battery voltages may range from 100 to 1000 V DC (VDC).

[0018] come Figure 2, the figure shows an overall schematic diagram of a common mode filter 30, which has a magnetic core 30a and three filter windings 30b, which are connected in series with the three-phase stator windings (U, V, W) included with the motor 16. The common mode filter includes a magnetic core 30a and a filter winding 30b wound on the magnetic core 30a. The filter winding 30b may include three separate windings, which are wound in the same direction as the stator windings (U, V, W), and each of the three filter windings 30b can be individually connected to one phase of the winding. The magnetic core 30a can be an iron ring, and the filter winding 30b is wound on the iron ring. However, the magnetic core 30a can be formed by any of a variety of different materials, such as powder cores, ferrites, iron laminations or other types of soft magnetic materials. The three-phase stator winding is electrically arranged in the stator of the motor 16 with a Delta connection instead of a Wye connection. The Delta connection involves three separate stator windings (U, V, W) that are electrically connected together in a loop and, unlike the Wye connection, do not have a neutral line. The Delta arrangement can produce circulating currents that include third harmonic currents in each of the stator windings (U, V, W). In contrast, in the Wye arrangement, the vectors of the third harmonic voltages in each phase of the stator windings are the same and cancel each other out, so that there is no circulating current due to the third harmonic. However, in the Delta connection, the vectors of the third harmonic voltages are superimposed in the Delta loop formed, so that there is a circulating current. The number of windings and the specifications of the windings may vary depending on the implementation.

[0019] Figure 3A partial view of another implementation of a common mode filter 31 is depicted, which is coupled to a stator 32a of an electric motor 16. It is a pole segment of a multi-pole motor. The common mode filter 31 includes a magnetic core 31a and a filter winding 31b wound on the magnetic core 31a. The stator 32a includes a stator slot 36 that receives three stator windings (U, V, W). The magnetic core 31a is shown as a single integral structure having a length of three filter windings 31b, which extend away from a radially extending surface 34 of the stator 32a and are wound around the periphery of the common mode filter magnetic core 31a. The filter windings 31b can each be connected in series with one of the stator windings (U, V, W). A section of filter winding 31b electrically connected to the U stator winding can be wound around the core 31a for a circumferential length (L), a section of filter winding 31b electrically connected to the V stator winding can be wound around the core 31a for an adjacent circumferential length of the common mode filter 31, and a section of filter winding 31b electrically connected to the W stator winding can be wound around the core 31a for a circumferential length of the common mode filter 31 adjacent to the V winding section. As long as the filter windings for each phase have an equal number of turns, the filter winding arrangement is flexible. In this implementation, the common mode filter 31 can be attached to the radially extending surface 34 of the stator 32a as a single integral element having a relatively circular cross-sectional shape. However, it should be clear that other implementations are also possible in which different cross-sectional shapes are selected, or multiple common mode filters can be attached to the stator.

[0020] Figure 4 A partial view of an implementation of a common mode filter 33 integrated with a back iron section 38 of a stator 32b is depicted. It is a pole segment of a multi-pole motor. The stator 32b includes a plurality of stator slots 36, a back iron region 38, and a plurality of holes 39 located at the junction of the stator teeth and the stator back iron for receiving filter wires. The common mode filter 33 uses the back iron region 38 as a magnetic core and includes filter wires 33b. A plurality of grooves 40 may be formed on the back iron region 38 and extend axially in a direction substantially parallel to the slots 36. Three filter windings 33b may be wound on the back iron region 38 of the stator 32b, passing through the holes 39 and fitting in the grooves 40. A section of filter winding 31b is wound around the back iron area 38 and connected to the U stator winding for a circumferential length (L), a section of filter winding 33b is wound around the back iron area 38 and connected to the V stator winding for a circumferential length (L), and a section of filter winding 33b is wound around the back iron area 38 and connected to the W stator winding for a circumferential length (L).

[0021] 5-6 depict the results of the analysis of the operation of the motor with and without the common mode filter 30. FIG. 5a is a graph of the simulated current in the stator windings (U, V, W) of the motor 16 without the common mode filter 30 versus time, while FIG. 5b is a graph of the simulated current in the stator windings (U, V, W) of the motor 16 with the common mode filter 30 versus time. FIG. 6a is a graph of the simulated torque output of the motor 16 without the common mode filter 30 versus time, while FIG. 6b is a graph of the simulated torque of the motor 16 with the common mode filter 30 versus time. Before the application of the common mode filter 30, the motor 16 outputs an average torque of 1084 Nm (337 Nm peak-to-peak ripple) and high third harmonics in the phase current. After the application of the common mode filter 30, the motor 16 outputs an average torque of 1148 Nm (135 Nm peak-to-peak ripple) and low harmonics in the phase current. The addition of the common mode filter 30 can produce a 20% reduction in copper losses, a 6% increase in torque output, and a more than 60% reduction in peak-to-peak torque ripple.

[0022] It should be understood that the above is a description of one or more embodiments of the present invention. The present invention is not limited to the specific embodiments disclosed herein, but is limited only by the following claims. In addition, the statements contained in the above description relate to specific embodiments and are not considered to be limitations on the scope of the present invention or the definitions of the terms used in the claims, unless a term or phrase is clearly defined above. Various other embodiments and various changes and modifications to the disclosed embodiments will become clear to those skilled in the art. All of these other embodiments, changes and modifications are within the scope of the appended claims.

[0023] As used in this specification and claims, the terms "example," "for example," "such as," and "like," and the verbs "include," "have," "comprises," and their other verb forms, when used in conjunction with a list of one or more components or other items, are each considered open-ended, meaning that the list is not considered to exclude other additional components or items. Other terms are interpreted using their broadest reasonable meaning unless they are used in a context that requires another interpretation.

Claims

1. A three-phase alternating current (AC) synchronous motor, comprising: a stator having a plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; as well as A common mode filter is included with the stator, wherein a filter winding from the common mode filter is circumferentially wound on a magnetic core of the common mode filter and connected in series to the stator winding. 2 . The three-phase AC synchronous motor of claim 1 , further comprising an electric vehicle (EV) operably coupled to the three-phase AC synchronous motor.

3. The three-phase AC synchronous motor according to claim 1, wherein: The magnetic core of the common mode filter is a single integral structure.

4. The three-phase AC synchronous motor according to claim 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 motor, comprising: a stator having a plurality of stator slots and a back iron region located axially outward from the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; as well as A common mode filter includes a magnetic core positioned adjacent to an outer surface of the stator, wherein a filter winding from the common mode filter is circumferentially wound on the magnetic core and connected in series to the plurality of stator windings. 6 . The three-phase AC synchronous motor of claim 5 , further comprising an electric vehicle (EV) operably coupled to the three-phase alternating current (AC) synchronous motor.

7. The three-phase AC synchronous motor according to claim 5, wherein: The magnetic core of the common mode filter is a single integral structure.

8. The three-phase AC synchronous motor according to claim 5, wherein: A magnetic core of the common mode filter is coupled to a radially extending surface of the stator.

9. The three-phase AC synchronous motor according to claim 5, wherein: The magnetic core of the common mode filter has a circular or rectangular cross-sectional shape.

10. The three-phase AC synchronous motor according to claim 5, wherein: The magnetic core of the common mode filter is ring-shaped.

11. A three-phase alternating current (AC) synchronous motor, comprising: a stator having a plurality of stator slots and a back iron region located radially outward from the plurality of stator slots; a plurality of stator windings arranged in a delta connection and received in the stator slots; as well as A common mode filter includes a magnetic core integrated with the stator, wherein a filter winding from the common mode filter is wound on the stator and connected in series to the plurality of stator windings.

12. The three-phase AC synchronous motor of claim 11, further comprising an electric vehicle (EV) operably coupled to the three-phase alternating current (AC) synchronous motor. 13 . The three-phase AC synchronous motor of claim 11 , further comprising a plurality of slots and holes formed in the stator and shaped to receive a filter winding wound on the stator.

14. The three-phase AC synchronous motor according to claim 11, wherein: The filter winding is wound on a back iron region of the stator.

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