Electric motor system

Abstract

To achieve a higher rotational speed.SOLUTION: A rotary machine system 100 comprises: a motor 2; an inverter 9 which supplies, to the motor 2, electric power required by the motor 2; and electric power lines 8U, 8V, and 8W which electrically connect the inverter 9 to the motor 2. One end of each of the electric power lines 8U, 8V, and 8W is connected to the motor 2. The other end of each of the electric power line 8U, 8V, and 8W is connected to the inverter 9. The electric power lines 8U, 8V, and 8W each have a bus bar 81 which includes a portion made of a magnetic material.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an electric motor system. [Background technology]

[0002] Patent Documents 1 and 2 disclose technologies related to sensorless drive motors. Both of the technologies disclosed in Patent Documents 1 and 2 address noise that occurs in induced voltages. Patent Document 1 employs a method of incorporating electrical elements such as capacitors and resistors into the circuit as a countermeasure against noise. Patent Document 2 employs a method using signal processing as a countermeasure against noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-126103 A [Patent Document 2] JP 2014-166097 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for electric motors to rotate at even higher speeds. To achieve higher speeds, it is important to take measures against noise, as signals with superimposed noise interfere with the rotation control of the motor. As mentioned above, noise countermeasures include a method of incorporating electric elements into the circuit and a method using signal processing. The method of incorporating electric elements into the circuit converts noise components into electrical loss and releases them as heat. Therefore, the electric elements that convert noise components into electrical loss become very hot. Furthermore, with the method using signal processing, there are cases where the signal processing cannot keep up with the high rotation speed of the motor. Therefore, it has been difficult to increase the rotation speed of electric motors.

[0005] Therefore, the present invention provides an electric motor system capable of high speed rotation. [Means for solving the problem]

[0006] An electric motor system according to one embodiment of the present invention comprises an electric motor, a power conversion device that provides the electric power required by the electric motor to the electric motor, and a power line that electrically connects the power conversion device to the electric motor, one end of the power line being connected to the electric motor and the other end of the power line being connected to the power conversion unit, and the power line having a bus bar including a portion made of a magnetic material.

[0007] This electric motor system has a bus bar that connects the electric motor and the power conversion device. The bus bar functions as a resistance component that has a high resistance value against high-frequency components of a current that contribute to the generation of noise, thereby enabling the electric motor to rotate at high speed.

[0008] In the electric motor system described above, one end of the bus bar is connected to the power conversion device, and the other end of the bus bar is connected to the electric motor. This configuration also makes it possible to reduce high-frequency noise components superimposed on a signal used for controlling the rotation of the electric motor.

[0009] In the electric motor system described above, the bus bar may be made only of a magnetic material. This configuration also makes it possible to reduce high-frequency noise components superimposed on signals used to control the rotation of the electric motor.

[0010] In the above electric motor system, the bus bar may include a first region that is a portion made of a magnetic material and a second region that is a portion made of a material having a different conductivity from the magnetic material, and the first region may form a surface of the bus bar. This configuration also makes it possible to reduce high-frequency noise components superimposed on a signal used to control the rotation of the electric motor. Effect of the Invention

[0011] According to the electric motor system of the present invention, high speed rotation is possible. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an electric motor system according to an embodiment. [Diagram 2] FIG. 2 is a circuit diagram of the inverter shown in FIG. [Diagram 3] FIG. 3 is a table for explaining the operation of the inverter and the motor shown in FIG. [Figure 4] Figure 4(a) is a graph showing the rotor phase, Figure 4(b) is a graph showing the U-phase voltage, Figure 4(c) is a graph showing the V-phase voltage, and Figure 4(d) is a graph showing the W-phase voltage. [Diagram 5] FIG. 5 is a circuit diagram showing a first operation of the inverter and the motor shown in FIG. [Figure 6] FIG. 6 is a circuit diagram showing a second operation of the inverter and the motor shown in FIG. [Figure 7] FIG. 7 is an equivalent circuit diagram for explaining the operation of the inverter and the motor shown in FIG. [Figure 8] FIG. 8 is a graph for explaining electrical problems in the inverter and the motor. [Figure 9] FIG. 9 is a configuration diagram of an electric motor system including a motor and an inverter connected by a bus bar. [Figure 10] Fig. 10(a) is a cross-sectional view of a bus bar that electrically connects an inverter and a motor to each other, Fig. 10(b) is a cross-sectional view of a bus bar of Modification 1, and Fig. 10(c) is a cross-sectional view of a bus bar of Modification 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals and duplicated descriptions will be omitted.

[0014] 1 is a two-stage centrifugal compressor. The rotating machine system 100 includes a rotating machine 1 and an inverter 9 (power conversion device).

[0015] The rotating machine 1 has a motor 2 (electric motor), a cooling jacket 3, a cooling device 4, and a pair of compressors 6. The motor 2 is provided with a rotating shaft 21, and impellers 61 of the compressor 6 are connected to both ends of the rotating shaft 21. The cylindrical rotating shaft 21 is supported by a pair of bearings 7 and rotates about its axis L relative to a motor housing 26. The cooling jacket 3 recovers heat generated by the operation of the motor 2 using a cooling medium supplied from the cooling device 4. The cooling medium is, for example, water.

[0016] The motor 2 has a motor housing 26. The motor housing 26 accommodates the cooling jacket 3 and the like. The cooling device 4 may be disposed outside the motor housing 26 as shown in FIG. 1, or may be accommodated inside the motor housing 26. The motor housing 26 has, for example, a cylindrical shape. The integrated motor 2 and cooling jacket 3 are fixed to the inner circumferential surface of the motor housing 26. The motor housing 26 is made of, for example, ductile cast iron (Ferrum Casting Ductile: FCD). A bearing casing 63 supporting the bearings 7 is provided on the inner circumferential side of the motor housing 26 at both ends in the axial direction D.

[0017] The motor 2 is a so-called brushless DC motor. The motor 2 has a rotor 22 and a stator 23. An alternating current is provided to the stator 23. An interaction between the rotor 22 and the stator 23 generates a torque in the rotor 22. As a result, the rotating shaft 21 fixed to the rotor 22 rotates.

[0018] The rotor 22 is attached to the rotating shaft 21. The position where the rotor 22 is fixed is approximately the center of the rotating shaft 21 in the axial direction D (hereinafter simply referred to as the "axial direction D").

[0019] The stator 23 surrounds the rotor 22 along the circumferential direction of the rotating shaft 21. The stator 23 includes a stator core 231 and a stator coil 232. The cylindrical stator core 231 extending along the axis L is provided so as to surround the rotor 22. The stator coil 232 is formed of a conductor wound around the stator core 231. In the stator coil 232, a portion protruding from the stator core 231 is a so-called coil end 232a. The coil end 232a protrudes in the axial direction D beyond both ends of the stator core 231.

[0020] The cooling jacket 3 is provided around the stator 23. That is, the cooling jacket 3 surrounds the stator 23 in the circumferential direction. The cooling jacket 3 also surrounds a part of the rotating shaft 21 and the rotor 22 that protrudes in the axial direction D beyond the end of the stator 23. The cooling jacket 3 is formed with a cooling flow passage 30 through which a cooling medium flows.

[0021] The cooling flow passage 30 is formed to revolve around the axis L of the rotating shaft 21. The cooling flow passage 30 has a flow passage inlet and a flow passage outlet. The flow passage inlet of the cooling flow passage 30 is connected to a supply pipe 41. The flow passage outlet is connected to a discharge pipe 42.

[0022] The cooling jacket 3 has a cylindrical inner housing 31 surrounding the stator 23, and a cylindrical outer housing 32 that is fitted to the inner housing 31. The inner housing 31 and the outer housing 32 are, for example, cast metal, and examples of materials include aluminum (Al) or cast iron. The cooling jacket 3 made by casting has a cast surface, and therefore has a relatively large surface roughness. When the surface roughness is large, the surface area tends to increase, which is advantageous from the viewpoint of heat transfer. The cooling jacket 3 may be made by three-dimensional molding instead of casting. The outer housing 32 surrounds the inner housing 31. The inner housing 31 is fixed to the outer housing 32 by bolts.

[0023] The inner housing 31 has a spiral flow passage groove 311 provided on the outer circumferential surface of the inner housing 31. In other words, the flow passage grooves 311 are each formed continuously so as to revolve around the axis L of the rotating shaft 21 as the center.

[0024] The opening of the flow passage groove 311 is closed by the inner circumferential surface of the outer housing 32. In other words, the inner circumferential surface of the outer housing 32 is in close contact with the outer circumferential surface of the inner housing 31.

[0025] The inverter 9 supplies so-called three-phase AC power to the motor 2. The inverter 9 is connected to the motor 2 via three power lines 8. The three power lines 8 correspond to the so-called U phase, V phase, and W phase.

[0026] Fig. 2 is a circuit diagram of the inverter 9 shown in Fig. 1. The inverter 9 outputs three-phase AC power by controlling the on / off of multiple switching elements. The inverter 9 has a power supply unit 91, a U-phase leg 92, a V-phase leg 93, and a W-phase leg 94.

[0027] The power supply unit 91 includes DC power supplies 911 and 912. The DC power supply 911 generates a positive voltage (+Vdc / 2). The DC power supply 912 generates a negative voltage (-Vdc / 2). The negative electrode of the DC power supply 911 is connected to the positive electrode of the DC power supply 912, and the negative electrode of the DC power supply 911 and the positive electrode of the DC power supply 912 are both connected to a reference potential 913.

[0028] U-phase leg 92 has a U-phase upper arm 921 and a U-phase lower arm 922. U-phase upper arm 921 and U-phase lower arm 922 are each formed by a switching element. U-phase upper arm 921 and U-phase lower arm 922 are connected in series. A U-phase output terminal 923 is provided on a line connecting U-phase upper arm 921 to U-phase lower arm 922. U-phase output terminal 923 is connected to U-phase power line 8U.

[0029] The V-phase leg 93 and the W-phase leg 94 have the same configuration as the U-phase leg 92. That is, the V-phase leg 93 has a V-phase upper arm 931 and a V-phase lower arm 932. A V-phase output terminal 933 is provided on the line connecting the V-phase upper arm 931 to the V-phase lower arm 932. The V-phase output terminal 933 is connected to the V-phase power line 8V. The W-phase leg 94 has a W-phase upper arm 941 and a W-phase lower arm 942. A W-phase output terminal 943 is provided on the line connecting the W-phase upper arm 941 to the W-phase lower arm 942. The W-phase output terminal 943 is connected to the W-phase power line 8W.

[0030] 2 also shows an equivalent circuit of the motor 2, which includes the inductor 24 and an induced voltage generating element 25. The induced voltage generating element 25 visualizes the induced voltage generated by the rotation of the rotor 22 for the purpose of explanation.

[0031] The inverter 9 shown in Fig. 2 repeats six operation modes M1 to M6 shown in the table of Fig. 3. Fig. 4(a) shows the phase of the rotor 22 in each of the operation modes M1 to M6. Fig. 4(b), Fig. 4(c), and Fig. 4(d) show the U-phase voltage, V-phase voltage, and W-phase voltage in each of the operation modes M1 to M6.

[0032] When "voltage detection" is written in the table of Fig. 3, the inverter 9 does not operate, but performs an operation of detecting the induced voltage from the motor 2. For example, in the operation mode M1, the U phase is in "voltage detection". Therefore, the pulse-shaped graphs G4b, G4c, and G4d shown in Fig. 4(b), Fig. 4(c), and Fig. 4(d) show the induced voltage of the motor 2.

[0033] The operation modes M1 to M6 are switched in sequence based on the timing when the reference voltage is exceeded. For example, when the phase advances by 30 degrees from the timing when the induced voltage exceeds zero, the operation modes are switched in sequence to the next operation modes M1 to M6. The timing when the induced voltage exceeds zero can be known by judging the so-called zero crossing. The zero crossing can be judged from the induced voltage output by each phase that detects the voltage.

[0034] In the examples shown in Figures 4(b), 4(c), and 4(d), the induced voltage is shown as a pulse-like waveform. Zero-crossings can be determined by either an analog circuit or digital processing. When using an analog circuit, the pulse-like signal indicating the induced voltage is passed through a low-pass filter. When using digital processing, a microcomputer is used to obtain the detected voltage in accordance with the MWM period.

[0035] The reason why the induced voltage is output as a pulse waveform as shown in FIGS. 4(b), 4(c) and 4(d) will be described.

[0036] For example, operation mode M1 will be taken as an example for detailed description. In operation mode M1, the U phase is in a voltage detection operation for detecting an induced voltage, the V phase is in a switching operation for outputting a PWM signal, and the W phase is in a conductive operation in which the W-phase upper arm 941 is always ON. In operation mode M1 in which these operations are performed, the V-phase lower arm 932 repeatedly turns ON or OFF. The V-phase upper arm 931 and the V-phase lower arm 932 operate in a complementary manner. This complementary operation makes it possible to suppress inverter loss during reflux.

[0037] First, when the switching element constituting V-phase lower arm 932 is ON, switching element 931S constituting V-phase upper arm 931 is OFF. Fig. 5 shows a first state in which V-phase lower arm 932 is ON and V-phase upper arm 931 is OFF in operation mode M1. In the first state shown in Fig. 5, the average value of the output voltage of inverter 9 is the reference potential (GND). Furthermore, in the first state, the intermediate potential of motor 2 is also the reference potential (GND). In the first state, the voltage detected in U-phase is only the induced voltage.

[0038] Next, when the switching element constituting V-phase lower arm 932 is OFF, switching element 931S constituting V-phase upper arm 931 is ON. Fig. 6 shows a second state in which V-phase lower arm 932 is OFF and V-phase upper arm 931 is ON in operation mode M1. In the second state shown in Fig. 6, the average value of the output voltage of inverter 9 is a positive voltage (+Vdc / 2). Furthermore, in the second state, the intermediate potential of motor 2 is also a positive voltage (+Vdc / 2). And, in the second state, the voltage detected in U-phase is a positive voltage (+Vdc / 2).

[0039] Here, if the induced voltage is positive, a positive voltage (+Vdc / 2) is added to the induced voltage, which exceeds the positive voltage (+Vdc / 2) output by DC power supply 911. In this case, a flywheel diode (not shown) provided in U-phase upper arm 921 is energized. As a result, the maximum value of the voltage detected in the U-phase becomes a positive voltage (+Vdc / 2).

[0040] To summarise the first and second states, the ON / OFF switching operation of the V-phase lower arm 932 in the operation mode M1 causes the intermediate potential of the motor 2 to become a pulsed signal which goes back and forth between the reference potential (GND) and a positive voltage (+Vdc / 2). As a result, the voltage detected in the U-phase also becomes a pulsed signal.

[0041] As described above, the operation modes M1 to M6 shown in Fig. 2 are switched sequentially based on the zero-cross timing. Therefore, accurately grasping the zero-cross timing is an important issue in controlling the motor 2 in sensorless operation.

[0042] According to an ideal circuit, the waveform of the induced voltage for obtaining the timing of the zero crossing is as shown in FIG. 4(b), FIG. 4(c), and FIG. 4(d). However, in an actual circuit, so-called parasitic resistance and parasitic capacitance exist. FIG. 7 is a circuit diagram showing an equivalent circuit when the U-phase is the voltage detection phase. As shown in FIG. 7, the equivalent circuit for detecting the induced voltage includes an inductor 24 caused by the winding of the motor 2, a parasitic resistance element 8R caused by the U-phase power line 8U connecting the motor 2 and the inverter 9, and parasitic capacitance elements 931C and 932C caused by the switching elements 931S and 932S.

[0043] These electrical elements form a so-called LCR series circuit. The LCR series circuit has a natural resonant frequency. When the switching frequency of the switching element approaches the resonant frequency of the equivalent circuit, the induced voltage contains noise caused by the resonance.

[0044] The graph in Figure 8 is an example of the measured value of the induced voltage. Graph G8 includes several peaks P8. The multiple peaks P8 are high-frequency noise components caused by resonance. If such noise components are included in the waveform of the induced voltage, it will affect the determination of the zero crossing.

[0045] In other words, if the switching frequency of the inverter 9 is increased in accordance with the increased speed of the motor 2, the frequency approaches the resonant frequency of the circuits included in the inverter 9 and the motor 2, and as a result, noise caused by resonance is superimposed on the induced voltage. When noise is superimposed on the induced voltage, it affects the determination of the zero crossings required for controlling the motor 2. As a result, the motor 2 is prevented from rotating at a higher speed.

[0046] Therefore, the rotating machine system 100 of the embodiment has a configuration for suppressing noise caused by resonance. Specifically, the Q value, which indicates the degree to which the amplitude increases due to resonance, is reduced. Refer again to the equivalent circuit shown in Fig. 7. The Q value of this equivalent circuit is expressed by equation (1). Q = ω × L / R (1) Q: Quality factor. ω: switching frequency. L: Motor 2 inductor. R: Parasitic resistance.

[0047] According to the formula (1), it can be seen that in order to reduce the Q value on the left side, the parasitic resistance R included in the denominator on the right side should be increased. Therefore, the rotating machine system 100 has a configuration for increasing the value of the parasitic resistance element 8R shown in the equivalent circuit of FIG.

[0048] 9 is a diagram showing a schematic diagram of a connection configuration between the motor 2 and the inverter 9. The inverter 9 is connected to the motor 2 via three power lines 8U, 8V, and 8W. These power lines 8U, 8V, and 8W are configured by so-called bus bars 81. The motor 2 has a motor terminal block 27 provided in the motor housing 26. The inverter 9 also has an inverter terminal block 97 provided in the inverter housing 96.

[0049] The bus bar 81 has a motor side connection portion 811 fixed to the motor terminal block 27 and an inverter side connection portion 812 fixed to the inverter terminal block 97. The bus bar 81 is an integral member formed of a conductive magnetic material. In other words, the entire wiring from the inverter terminal block 97 to the motor terminal block 27 is formed by the bus bar 81. In this embodiment, a thin wire thinner than the bus bar 81 or a twisted wire made of twisted thin wires is connected to the motor side of the motor terminal block 27 and the inverter side of the inverter terminal block 97.

[0050] For example, as shown in FIG. 10(a), the cross-sectional shape of a busbar 81 is circular. The busbar 81 shown in FIG. 10(a) is formed of a magnetic material having electrical conductivity over the entire cross-section. When a current containing a high-frequency component is passed through such a busbar 81, the high-frequency component is conducted only to a region near the surface of the busbar 81. As a result, the busbar 81 functions as a resistive component having a high resistance value against the high-frequency component of the current that contributes to the generation of noise. This phenomenon is called the "skin effect." The effect of the skin effect can be further enhanced by employing a magnetic material. Furthermore, the effect can also be enhanced by reducing the surface area by forming the cross-section in a circular shape.

[0051] The skin effect of the bus bar 81 converts noise components into heat. As a result, the noise components are reduced. Furthermore, the bus bar 81 is an integrated component extending from the inverter terminal block 97 to the motor terminal block 27. In other words, the bus bar 81 is not surrounded by other components and is placed in an advantageous position for cooling, exposed to the outside air. As a result, heat generated by the bus bar 81 is efficiently dissipated into the air surrounding the bus bar 81. Therefore, there is no need to add components for cooling the bus bar 81. However, this description does not prevent the addition of components for cooling the bus bar 81.

[0052] The rotating machine system 100 includes a motor 2, an inverter 9 that provides the motor 2 with power required by the motor 2, and power lines 8U, 8V, and 8W that electrically connect the inverter 9 to the motor 2. One end of each of the power lines 8U, 8V, and 8W is connected to the motor 2. The other end of each of the power lines 8U, 8V, and 8W is connected to the inverter 9. The power lines 8U, 8V, and 8W have a bus bar 81 that includes a portion made of a magnetic material.

[0053] The rotating machine system 100 has a bus bar 81 that connects the motor 2 and the inverter 9. The bus bar 81 functions as a resistance component that has a high resistance value against high-frequency components of a current that contribute to the generation of noise. Therefore, the motor 2 can be rotated at a high speed.

[0054] The bus bar 81 includes a motor side connection portion 811 connected to the motor 2 and an inverter side connection portion 812 connected to the inverter 9 .

[0055] The bus bar 81 is made entirely of a magnetic material.

[0056] The present disclosure is not limited to the above-described embodiment, and various modifications as described below are possible without departing from the gist of the present disclosure.

[0057] For example, as shown in Fig. 10(b), the cross-sectional shape of busbar 81A may be rectangular. Even with such busbar 81A, noise components can be reduced by the skin effect. Alternatively, the cross-sectional shape is not limited to rectangular, and may be a regular polygon, ellipse, oval, or the like. A busbar having a surface shape that does not include a recess that leads to an increase in surface area may also be used.

[0058] For example, as shown in FIG. 10(c), the busbar 81B may be formed by combining different materials. The busbar 81B includes a first region 821 and a second region 822. The first region 821 is a portion formed of a magnetic material. The second region 822 is a portion formed of a material having a different conductivity from the magnetic material. The first region 821 forms the surface of the busbar 81B. The first region 821 covers the second region 822. That is, the busbar 81B shown in FIG. 10(c) is formed of a magnetic material only near the surface, and not near the center. Even in such a busbar 81B, a skin effect can be obtained by the magnetic material forming the first region 821, so that noise components can be reduced. [Explanation of symbols]

[0059] 1 Rotating Machinery 2. Motor (electric motor) 9. Inverter (power conversion device) 8U,8V,8W power line 81, 81A, 81B Busbar 811 Motor side connection part 812 Inverter side connection part 821 First Area 822 Second Area

Claims

1. An electric motor; a power converter for providing the electric motor with the electric power required by the electric motor; a power line electrically connecting the power conversion device and the electric motor, One end of the power line is connected to the electric motor, The other end of the power line is connected to the power conversion device, An electric motor system, wherein the power line has a bus bar including a portion made of a magnetic material.

2. One end of the bus bar is connected to the power conversion device, The electric motor system according to claim 1 , wherein the other end of the bus bar is connected to the electric motor.

3. The electric motor system according to claim 1 , wherein the bus bar is composed only of the magnetic material.

4. the bus bar includes a first region that is a portion configured from the magnetic material, and a second region that is a portion configured from a material having electrical conductivity different from that of the magnetic material, The electric motor system of claim 1 , wherein the first region forms a surface of the bus bar.

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