Current detection device

[00002] This invention relates to a device for detecting the currents of a plurality of rotating electric machines.

[00003] When supplying current to the stator of a rotating electric machine through a supply line from an inverter, the current flowing in the supply line is detected by providing a current sensor in the supply line.

[00004] U.S. Pat. No. 6,049,152 issued to Masaki Nakano on 11 Apr. 2000 discloses a composite motor provided with a plurality of rotating electric machines controlled by a single inverter. The single inverter supplies the composite motor with a composite current containing a plurality of current components having their respective frequencies. The respective frequency of the current component is determined in response to the rotational frequency of each rotating electric machine.

[00005] It is an object of this invention to perform separate detection of the current components with their respective frequencies constituting a composite current when a plurality of rotating electric machines are controlled by a single inverter.

[00006] In order to achieve above object, this invention provides a current detection device for use in an electric rotating system, the system having a first rotor, a second rotor, and a single inverter for supplying a composite current which is a combination of a first current component for driving the first rotor and a second current component for driving the second rotor. The first current component has a first frequency and the second current component having a second frequency which is different from the first frequency. The composite current flows in each supply line connected to the inverter. The inverter supplies the composite currents so that the first current components flow with the same phases and the second current components flow with different phases from one another in a plurality, N, of supply lines. Here, the second current components deviate at regular phase intervals of (360/N)°, thus having a phase difference of (360/N)°. The current detection device comprises a current sensor simultaneously detecting the currents in the N supply lines so that the current sensor detects only the first current component having the first frequency. Here, the current sensor does not detect the second current components of the second frequency because the second current components cancel out to zero.

[00007] The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.

[00013] Referring to FIG. 1, an example of a plurality of rotating electric machines using a common stator according to a first embodiment of this invention will be described. This example has two rotating electric machines. The two rotating electric machines use a common stator 2 and constitute an integrated composite motor 1. Rotors 3, 4 are disposed on the inside and outside of the cylindrical stator 2. The outer rotor 3 and the inner rotor 4 are disposed in a coaxial orientation with respect to the stator 2. The stator 2 and the outer rotor 3 make up one rotating electric machine. The inner rotor 4 and the stator 2 make up the other rotating electric machine.

[00014] More precisely, the inner rotor 4 has two pairs of magnetic poles. In the inner rotor 4, the S pole and the N pole are disposed alternately at an interval of 90°. The outer rotor 3 has twice the number of pairs of magnetic poles as the inner rotor 4. In other words, the outer rotor 3 has four N poles and four S poles which are disposed alternately at an interval of 45°.

[00015] The stator 2 has a triplet of coils per each magnetic pole of the inner rotor 4 making a total of 12 (=3×4) coils C1-C12 which are disposed at equal angular intervals on the same circular periphery.

[00016] A three-phase alternating current (Iu, Iv, Iw) generating a rotating magnetic field for rotating the outer rotor 3 flows in the twelve coils C1-C12. The current components of the three-phase alternating current have a phase difference of 120° (=2π/3) therebetween, as shown below.
Iu=Ic₁ cos(2πF₁t+α)  (1a)
 Iv=Ic₁ cos(2πF₁t−2π/3+α)  (1b)
Iw=Ic₁ cos(2πF₁t−4π/3+α)  (1c)

[00020] Where:

• • [00021] Ic₁: amplitude
  • [00022] F₁: frequency
  • [00023] α: initial phase angle

[00024] In the same manner, a six-phase alternating current (Ia, Ib, Ic, Id, Ie, If) generating a rotating magnetic field for rotating the inner rotor 4 flows in the twelve coils C1-C12. The current components of the three-phase alternating current have a phase difference of 60° (=π/3) therebetween, as shown below.
Ia=Ic₂ cos(2πF₂t+β)  (2a)
Ib=Ic₂ cos(2πF₂t−π/3+β)  (2b)
Ic=Ic₂ cos(2πF₂t−2π/3+β)  (2c)
Id=Ic₂ cos(2πF₂t−π+β)  (2d)
Ie=Ic₂ cos(2πF₂t−4π/3+β)  (2e)
If=Ic₂ cos(2πF₂t−5π/3+β)  (2f)

[00031] Where:

• • [00032] Ic₂: amplitude
  • [00033] F₂: frequency
  • [00034] β: initial phase angle

[00035] Consequently, when the currents which flow in the coils C1-C12 in order to control the outer rotor (hereafter referred to as “outer-rotor currents”) are designated as I₁1-I₁12, these currents are given as shown below using Equation (1).
I₁1=Iu=Ic₁ cos(2πF₁t+α)  (3a)
I₁2=Iv=Ic₁ cos(2πF₁t−2π/3+α)  (3b)
I₁3=Iw=Ic₁ cos(2πF₁t−4π/3+α)  (3c)
I₁4=Iu=Ic₁ cos(2πF₁t+α)  (3d)
I₁5=Iv=Ic₁ cos(2πF₁t−2π/3+α)  (3e)
 I₁6=Iw=Ic₁ cos(2πF₁t−4π/3+α)  (3f)
I₁7=Iu=Ic₁ cos(2πF₁t+α)  (3g)
I₁8=Iv=Ic₁ cos(2πF₁t−2π/3+α)  (3h)
I₁9=Iw=Ic₁ cos(2πF₁t−4π/3+α)  (3i)
I₁10=Iu=Ic₁ cos(2πF₁t+α)  (3j)
I₁11=Iv=Ic₁ cos(2πF₁t−2π/3+α)  (3k)
I₁12=Iw=Ic₁ cos(2πF₁t−4π/3+α)  (3l)

[00048] In the same manner, when the currents which flow in the coils C1-C12 in order to control the inner rotor (hereafter referred to as “inner-rotor currents”) are designated as I₂1-I₂12, these currents are given as shown below using Equation (2).
I₂1=Ia=Ic₂ cos(2πF₂t+β)  (4a)
I₂2=Ib=Ic₂ cos(2πF₂t−π/3+β)  (4b)
I₂3=Ic=Ic₂ cos(2πF₂t−2π/3+β)  (4c)
I₂4=Id=Ic₂ cos(2πF₂t−π+β)  (4d)
I₂5=Ie=Ic₂ cos(2πF₂t−4π/3+β)  (4e)
I₂6=If=Ic₂ cos(2πF₂t−5π/3+β)  (4f)
I₂7=Ia=Ic₂ cos(2πF₂t+β)  (4g)
I₂8=Ib=Ic₂ cos(2πF₂t−π/3+β)  (4h)
I₂9=Ic=Ic₂ cos(2πF₂t−2π/3+β)  (4i)
I₂10=Id=Ic₂ cos(2πF₂t−π+β)  (4j)
I₂11=Ie=Ic₂ cos(2πF₂t−4π/3+β)  (4k)
I₂12=If=Ic₂ cos(2πF₂t−5π/3+β)  (4l)

[00061] Since the outer rotor 3 has four pairs of magnetic poles, the following relationship is established between the rotational angular velocity ω₁ of the outer rotor 3 and the frequency F₁ of the outer-rotor current.
ω₁=2πF₁/4  (5)

[00063] Since the inner rotor 4 has two pairs of magnetic poles, the following relationship is established between the rotational angular velocity ω₂ of the inner rotor 4 and the frequency F₂ of the inner rotor current.
ω₂=2πF₂/2  (6)

[00065] When the composite currents which flow in the coils C1-C12 of the stator 2 are designated as I1-I12, these currents may obviously be expressed as shown below using the current components Iu-Iw from Equation (1) and the current components Ia-If from Equation (2).
I1=Iu+Ia  (7a)
I2=Iv+Ib  (7b)
I3=Iw+Ic  (7c)
I4=Iu+Id  (7d)
I5=Iv+Ie  (7e)
I6=Iw+If  (7f)
I7=Iu+Ia  (7g)
I8=Iv+Ib  (7h)
I9=Iw+Ic  (7i)
I10=Iu+Id  (7j)
I11=Iv+Ie  (7k)
I12=Iw+If  (7l)

[00078] Since composite currents I1-I12 are set in this manner, two magnetic fields comprising the rotating magnetic field for rotating the outer rotor 3 and the rotating magnetic field for rotating the inner rotor 4 are simultaneously generated in a single coils unit C1-C12, that is to say, in a single stator. Consequently, the first rotating electric machine comprising the outer rotor 3 and the stator 2 and the second rotating electric machine comprising the inner rotor 4 and the stator 2 are independently controlled. The rotating magnetic field for rotating the outer rotor 3 does not apply a rotational force to the inner rotor 4 and the rotating magnetic field for rotating the inner rotor 4 does not apply a rotational force to the outer rotor 3. The principle for this is disclosed in U.S. Pat. No. 6,049,152.

[00079] The setting of the current components Iu, Iv, Iw is performed in synchrony with the rotational phase of the outer rotor 3 and the setting of the current components Ia, Ib, Ic, Id, Ie, If is performed in synchrony with the rotational phase of the inner rotor 4. An advance or delay of the current phase is set with respect to the direction of torque. This is the same as the settings performed in a synchronous motor.

[00080] The controller 8 shown in FIG. 2 is a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM) and an input/output interface (I/O interface). The controller 8 determines the command values for the d-axis and the q-axis currents for each rotating electric machine and performs a known vector control for each rotating electric machine. On the other hand, the actual values for the d-axis and the q-axis currents are calculated on the basis of the output signal from a rotational angle sensor for the outer rotor and the output signal from a rotational angle sensor for the inner rotor. The controller 8 generates a voltage command value for generating a three-phase current for the first rotating electric machine and a voltage command value for generating a six-phase current for the second rotating electric machine so that the actual d-axis current and the actual q-axis current coincide with the command values. A composite voltage command value is generated by combining the voltage command values for each rotating electric machine. A PWM signal is generated on the basis of the carrier signal and the composite voltage command value. The PWM signal is transmitted to the inverter 7 as shown in FIG. 2 and, FIG. 3.

[00081] Twelve composite currents I1-I12 as shown in Equation (7) flow from the inverter 7 through the supply lines 11-22 with respect to the twelve coils C1-C12 of the stator 2.

[00082] The composite motor 1 may be combined with the engine. This may be briefly described as directly connecting the outer rotor to the engine output shaft and directly connecting the inner rotor 4 to the drive shaft. The first rotating electric machine is mainly operated as a motor and the second rotating electric machine is mainly operated as a generator. In this case, the controller 8 is provided with the function of determining a target torque for the engine in addition to a target torque for the first rotating electric machine as well as a target torque and a target rotation speed for the second rotating electric machine.

[00083] Referring to FIG. 2 and FIG. 3, the position of the nine current sensors (only six are shown in FIG. 2 and FIG. 3) for the twelve supply lines 11-22 will be described. The current sensors are preferably through-type current sensors which detect a current based on the magnetic field generated by the current. The current sensor has a function of detecting the sum of the currents provided to the current sensor and is not limited to the through-type current sensor. A through-type current sensor is generally provided with a magnetic core through which the supply line passes. The magnetic field generated in the magnetic core by the current passing in the supply line is detected by a magnetic sensor such as a Hall sensor.

[00084] Referring to FIG. 2, when detecting the outer-rotor current, the supply lines 11, 14, 17, 20 to the coils 1, 4, 7, 10 are together led through a single current sensor 31. This current sensor 31 detects a current component Iu for the outer-rotor current. The detected value of the current sensor 31 is as shown below. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}31=\mathrm{I1}+\mathrm{I4}+\mathrm{I7}+\mathrm{I10}\\ =\left(I_{1}1+I_{1}4+I_{1}7+I_{1}10\right)+\\ \left(I_{2}1+I_{2}4+I_{2}7+I_{2}10\right)\end{array}& \left(8\right)\end{array}$

[00085] When Equation (3) and Equation (4) are substituted in the above equation, Equation (9) below is derived. Herein the initial phase angles α, β are normally set to zero. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}31=4\times {\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)+\\ \{{\mathrm{Ic}}_2\cos \left(2\pi F_{2}t\right)+\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t-\pi \right)+\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t\right)+\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t-\pi \right)\}\\ =4\times {\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)=4\times \mathrm{Iu}\end{array}& \left(9\right)\end{array}$

[00086] Since the terms Ic₂ cos(2πF₂t) and Ic₂ cos(2πF₂t−π) on the right side of the equation cancel out exactly, the result is obtained that {Ic₂ cos(2πF₂t)+Ic₂ cos(2πF₂t−π)} equals zero. That is to say, when the composite currents I1, I4, I7, I10 are detected together, the inner-rotor currents I₂1, I₂4, I₂7, I₂10 cancel out as a result of the relationship of their respective current phases and do not appear in the detection value of the current sensor 31.

[00087] Consequently the current sensor 31 detects only the current component Iu of the outer-rotor current multiplied by the number of pairs of magnetic poles. In this case, the multiple of pole pairs is four.

[00088] In the same manner, the supply lines 12, 15, 18, 21 to the coils C2, C5, C8, C11 are collected and pass through the same current sensor 32 as shown in FIG. 2. The supply lines 13, 16, 19, 22 to the coils C3, C6, C9, C12 are collected and pass through the same current sensor 33. In this manner, the remaining current components Iv, Iw for the outer-rotor current are detected as shown below as a multiple of four.
The detected value from the sensor 32=Ic₁ cos(2πF₁t−2π/3)=4×Iv  (10)
The detected value from the sensor 33=4×Ic₁ cos(2πF₁t−4π/3)=4×Iw  (11)

[00091] In this manner, all current components Iu, Iv, Iw can be determined by the three current sensors 31, 32, 33. The current sensor simultaneously detects the currents flowing in a set of two supply lines, such as (11,14), (17,20), (12,15), (18,21), (13,16), (19,22). In the set of two supply lines, current components, for example Iu, of the frequency F₁ flow in phase and current components, for example Ia and Id, of the frequency F₂ flow with different phases from one another. The current components of the frequency F₂ deviate at a regular phase interval of 180°. Thus, the second current components flow with opposite phases to one another in the set of two supply lines.

[00092] Referring to FIG. 3, when the inner-rotor current is detected, the supply lines 11, 17 to the coils C1, C7 are collected with the supply lines 14, 20 to the coils C4, C10 which pass in the opposite direction through the current sensor 34, and applied to a single current sensor 34. If a direction in the supply line from the inverter 7 to the composite motor 1 is taken to be a plus direction, when the supply lines 11, 17 to the coils C1, C7 pass through the current sensor 34 in a plus direction from the inlet of the current sensor 34, the supply lines 14, 20 to the coils C4, C10 pass through the current sensor 34 in a minus direction from the inlet of the current sensor 34. Here the inlet of the current sensor 34 is on the left side of FIG. 3. In this manner, those current detection values generated by the supply lines 14, 20 to the coils C4, C10 have an opposite sign to other current detection values from the current sensor 34. Thus the current sensor 34 detects the 0°-phase current component Ia of the inner-rotor current as shown hereafter. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}34=\mathrm{I1}-\mathrm{I4}+\mathrm{I7}-\mathrm{I10}\\ =\left(I_{1}1-I_{1}4+I_{1}7-I_{1}10\right)+\\ \left(I_{2}1-I_{2}4+I_{2}7-I_{2}10\right)\end{array}& \left(12\right)\end{array}$

[00093] When Equation (3) and Equation (4) are substituted in the above equation, Equation (13) below is derived. Herein the initial phase angles α, β are normally set to zero. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}34=\{{\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)-\\ {\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)+\\ {\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)-\\ {\mathrm{Ic}}_1\cos \left(2\pi F_{1}t\right)\}+\\ \{{\mathrm{Ic}}_2\cos \left(2\pi F_{2}t\right)-\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t-\pi \right)+\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t\right)-\\ {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t-\pi \right)\}\\ =4\times {\mathrm{Ic}}_2\cos \left(2\pi F_{2}t\right)=4\times \mathrm{Ia}\end{array}& \left(13\right)\end{array}$

[00094] Since Ic₂ cos(2πF₂t) and −Ic₂ cos(2πF₂t−π) on the right side of the equation are equal (Ic₂ cos(2πF₂t)=−Ic₂ cos(2πF₂t−π)), the current component Ia of the inner-rotor current is detected as a multiple of four. Thus when the composite currents I1, −I4, I7, −I10 are detected together, the outer-rotor currents I₁1, I₁4, I₁7, I₁10 cancel out due to the relationship of the respective current phases and do not appear in the detected value.

[00095] In the same manner, referring to FIG. 3, the supply lines 12, 15, 18, 21 to the coils C2, C5, C8, C11 pass together through the current sensor 35. However the supply lines 12, 18 to the coils C2, C8 pass in the opposite direction through the current sensor 35 with respect to the supply lines 15, 21 to the coils C5, C11. Furthermore although the supply lines 13, 16, 19, 22 to the coils C3, C6, C9, C12 pass together through the current sensor 36, the supply lines 13, 19 to the coils C3, C9 pass in the opposite direction through the current sensor 35 with respect to the supply lines 16, 22 to the coils C6, C12. Likewise, although the supply lines 14, 17, 20, 21 to the coils C4, C7, C10, C1 pass together through a current sensor (not shown), the supply lines 14, 20 to the coils C4, C10 pass in the opposite direction through the current sensor with respect to the supply lines 17, 11 to the coils C7, C1. Although the supply lines 15, 18, 21, 12 to the coils C5, C8, C11, C2 pass together through a current sensor (not shown), the supply lines 15, 21 to the coils C5, C11 pass in the opposite direction through the current sensor with respect to the supply lines 18, 12 to the coils C8, C2. Although the supply lines 16, 19, 22, 13 to the coils C6, C9, C12, C3 pass together through a current sensor (not shown), the supply lines 6, 22 to the coils C6, C12 pass in the opposite direction through the current sensor to the supply lines 19, 13 to the coils C9, C3. The current components Ib, Ic, Id, Ie, If are detected as a multiple of four as shown below.
Detected value of sensor 35=4×Ic₂ cos(2πF₂t−π/3)=4×Ib  (14)
Detected value of sensor 36=4×Ic₂ cos(2πF₂t−2π/3)=4×Ic  (15)
 Detected value of sensor 37=4×Ic₂ cos(2πF₂t−π)=4×Id  (16)
Detected value of sensor 38=4×Ic₂ cos(2πF₂t−4π/3)=4×Ie  (17)
Detected value of sensor 39=4×Ic₂ cos(2πF₂t−5π/3)=4×If  (18)

[00101] In this manner, all the current components Ia, Ib, Ic, Id, Ie, If of the inner-rotor current are determined by six current sensors.

[00102] According to this embodiment, when the outer-rotor current, which has a frequency of F₁, is detected, the supply lines are collected and passed through the current sensors 31, 32, 33 so that the phases of the current components of the outer-rotor current of a frequency of F₁ are the same and the components of the inner-rotor current of a frequency of F₂ cancel out to a value of zero. When the inner-rotor current, which has a frequency of F₂, is detected, the supply lines are collected and passed through the current sensors 34, 35, 36 so that the phases of the current components of the inner-rotor current of a frequency of F₂ are the same and the components of the outer-rotor current of a frequency of F₁ cancel out to a value of zero.

[00103] In the first embodiment, the following effects are obtained.

[00104] (i) Since current components with respect to one rotating electric machine multiplied by the number of pole pairs is detected rather than a composite current, the SN ratio of the current sensors 31-36 can be improved in this embodiment in comparison to detecting a composite current in which there is a large difference between the average value and the maximum value.

[00105] (ii) It is possible to detect the current with little influence from the deviations in the performance of power devices such as an inverter 7 or deviations in the inductance of the supply lines 11-22 and stator coils C1-C12. As a result, the adverse effect of deviations in the inductance of the supply lines 11-22 and the coils C1-C12 is reduced in comparison to detecting a composite current for each supply line 11-22 and subsequently calculating the current components for a single rotating electric machine from the composite current.

[00106] (iii) The calculation load on the controller 8 is reduced. In this embodiment, since values of the current components Ia, Ib, Ic, Id, Ie, If of the inner-rotor current and for the current components Iu, Iv, Iw of the outer-rotor current which are multiplied by four (multiple of pole pair number) are detected by the current sensors 31-36, the controller 8 is not required to separate the current components from the composite current.

[00107] Referring to FIG. 4 and FIG. 5, a second embodiment will be described. In the second embodiment, the plurality of rotating electric machines are a first rotating electric machine 42 and a second rotating electric machine 43. These two rotating electric machines do not use a common stator. The number of pole pairs in the rotor of the first rotating electric machine 42 and the rotor of the second rotating electric machine 43 are both three. Hereafter the rotor of the first rotating electric machine 42 is termed the “first rotor” and the rotor of the second rotating electric machine 43 is termed the “second rotor”. The stators 44, 45 of each rotating electric machine have three coils per magnetic pole making a total of nine (3×3) coils. The stator 44 of the first rotating electric machine 42 is hereafter termed the “first stator” and the stator 45 of the second rotating electric machine 43 is hereafter termed the “second stator”. The rotating magnetic field with respect to the first rotor is generated by a three-phase current (Ip, Iq, Ir) deviating at a phase of 120° (2π/3) in the three coils as shown below.
Ip=Ic₃ cos(2πF₃t+γ)  (19a)
Iq=Ic₃ cos(2πF₃t−2π/3+γ)  (19b)
Ir=Ic₃ cos(2πF₃t−4π/3+γ)  (19c)
Where:

• • [00112] Ic₃: amplitude
  • [00113] F₃: frequency
  • [00114] γ: initial phase angle

[00115] In the same manner, a three-phase current (Ik, Il, Im) deviating at a phase of 120° (2π/3) is generated in order to produce a rotating magnetic field for rotating the second rotor as shown below.
Ik=Ic₄ cos(2πF₄t+δ)  (20a)
Il=Ic₄ cos(2πF₄t−2π/3+δ)  (20b)
Im=Ic₄ cos(2πF₄t−4π/3+δ)  (20c)
Where:

• • [00120] Ic₄: amplitude
  • [00121] F₄: frequency
  • [00122] δ: initial phase angle

[00123] Thus the currents (hereafter termed “first rotor current”) controlling the first rotor which flow in each of the nine coils D1-D9 of the first stator 44 are designated as I₃1-I₃9, they are given by the following equations.
I₃1=Ic₃ cos(2πF₃t+γ)  (21a)
I₃2=Ic₃ cos(2πF₃t−2π/3+γ)  (21b)
I₃3=Ic₃ cos(2πF₃t−4π/3+γ)  (21c)
I₃4=Ic₃ cos(2πF₃t+γ)  (21d)
I₃5=Ic₃ cos(2πF₃t−2π/3+γ)  (21e)
I₃6=Ic₃ cos(2πF₃t−4π/3+γ)  (21f)
I₃7=Ic₃ cos(2πF₃t+γ)  (21g)
I₃8=Ic₃ cos(2πF₃t−2π/3+γ)  (21h)
I₃9=Ic₃ cos(2πF₃t−4π/3+γ)  (21i)

[00133] In the same manner, when the currents (hereafter termed “second rotor current”) controlling the second rotor which flow in each of the nine coils E1-E9 of the second stator 45 are designated as I₄1-I₄9, they are given by the following equations.
I₄1=Ic₄ cos(2πF₄t+δ)  (22a)
I₄2=Ic₄ cos(2πF₄t+δ)  (22b)
I₄3=Ic₄ cos(2πF₄t+δ)  (22c)
I₄4=Ic₄ cos(2πF₄t−2π/3+δ)  (22d)
I₄5=Ic₄ cos(2πF₄t−2π/3+δ)  (22e)
I₄6=Ic₄ cos(2πF₄t−2π/3+δ)  (22f)
I₄7=Ic₄ cos(2πF₄t−4π/3+δ)  (22g)
I₄8=Ic₄ cos(2πF₄t−4π/3+δ)  (22h)
I₄9=Ic₄ cos(2πF₄t−4π/3+δ)  (22i)

[00143] In the case, the following relationship exists between the frequency F₃ for the first rotor current and the rotational angular velocity ω₃ of the first rotor.
ω₃=2πF₃/3  (23)

[00145] The following relationship exists between the frequency F4 for the second rotor current and the rotational angular velocity ω₄ of the second rotor.
ω₄=2πF₄/3  (24)

[00147] When the composite currents are taken to be I1-I9, they may obviously be expressed using the current components Ip-Ir in Equation (19) and the current components Ik-Im in Equation (20).
I1=Ip+Ik  (25a)
I2=Iq+Ik  (25b)
I3=Ir+Ik  (25c)
I4=Ip+Il  (25d)
I5=Iq+Il  (25e)
I6=Ir+Il  (25f)
 I7=Ip+Im  (25g)
I8=Iq+Im  (25h)
I9=Ir+Im  (25i)

[00157] The composite currents I1-I9 respectively are provided in the supply lines 111-119. However, the three-phase current (Ip, Iq, Ir) does not flow in the stator 45 of the second rotating electric machine 43 and the three-phase current (Ik, Il, Im) does not flow in the stator 44 of the first rotating electric machine 43 because each set of coils (D1, D2, D3) (D4, D5, D6) (D7, D8, D9) (E1, E4, E7) (E2, E5, E8) (E3, E6, E9) forms a three-phase coils unit in which three coils are connected by a star connection.

[00158] Six current sensors 51-56 are disposed in the following manner with respect to the total of nine supply lines 111-119. With respect to the first-rotor currents, in order to detect the 0°-phase current component Ip in the first-rotor current, the supply lines 111, 114, 117 to the coils D1, D4, D7 of the first stator 44 and the coils E1, E4, E7 of the second stator 45 are collected and pass through the current sensor 51. The detected value of the current sensor 51 is as follows. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}51=\mathrm{I1}+\mathrm{I4}+\mathrm{I7}\\ =\left(I_{3}1+I_{3}4+I_{3}7\right)+\\ \left(I_{4}1+I_{4}4+I_{4}7\right)\end{array}& \left(26\right)\end{array}$

[00159] Thus when Equation (21) and Equation (22) are substituted into this equation, the following equation is derived. Herein the initial phase angle γ and δ are set to a value of zero. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}51=3\times {\mathrm{Ic}}_3\cos \left(2\pi F_{3}t\right)+\\ \{{\mathrm{Ic}}_4\cos \left(2\pi F_{4}t\right)+\\ {\mathrm{Ic}}_4\cos \left(2\pi F_{4}t-2\pi /3\right)+\\ {\mathrm{Ic}}_4\cos \left(2\pi F_{4}t-4\pi /3\right)\}\\ =3\times {\mathrm{Ic}}_3\cos \left(2\pi F_{3}t\right)\\ =3\times \mathrm{Ip}\end{array}& \left(27\right)\end{array}$

[00160] Herein since {Ic₄ cos(2πF₄t)+Ic₄ cos(2πF₄t−2π/3)+Ic₄ cos(2πF₄t−4π/3)}=0, the second-rotor currents I₄I, I₄4, I₄7 do not appear in the detected value of the sensor 51. The detected value of the sensor 51 is the current component Ip of the first-rotor current which is multiplied by the number of pole pairs. In this embodiment, the multiple of pole pairs is three.

[00161] In the same manner, the supply lines 112, 115, 118 to the coils D2, D5, D8 in the first stator 44 and to the coils E2, E5, E8 in the second stator 45 are collected and pass through the same current sensor 52. The supply lines 113, 116, 119 to the coils D3, D6, D9 in the first stator 44 and to the coils E3, E6, E9 of the second stator 45 are collected and pass through the same current sensor 53. In this manner, the 120°- and 240°-phase current components Iq, Ir of the first-rotor current are detected as a multiple of three as shown below.
Detected value of sensor 52=3×Ic₃ cos(2πF₃t−2π/3)=3×Iq  (28)
Detected value of sensor 53=3×Ic₃ cos(2πF₃t−4π/3)=3×Ir  (29)

[00164] Thus all the current components Ip, Iq, Ir of the first-rotor current are determined by three current sensors 51-53.

[00165] In order to detect the 0°-phase current component Ik of the second-rotor current, the supply lines 111, 112, 113 to the coils D1, D2, D3, in the first stator 44 and to the coils E1, E2, E3, in the second stator 45 are collected and pass through the same current sensor 54.
Detected value of sensor 54=(I₃1+I₃2+I₃3)+(I₄1+I₄2+I₄3)  (30)

[00167] Thus when Equation (21) and Equation (22) are substituted into this equation, the following equation is derived. Herein the initial phase angle γ and δ are set to a value of zero. $\begin{array}{cc}\begin{array}{c}\mathrm{Detected}\mathrm{value}\mathrm{of}\mathrm{sensor}54=\{{\mathrm{Ic}}_3\cos \left(2\pi F_{3}t\right)+\\ {\mathrm{Ic}}_3\cos \left(2\pi F_{3}t-2\pi /3\right)+\\ {\mathrm{Ic}}_3\cos \left(2\pi F_{3}t-4\pi /3\right)\}+\\ 3\times {\mathrm{Ic}}_4\cos (2\pi F_{4}t)\\ =3\times {\mathrm{Ic}}_4\cos \left(2\pi F_{4}t\right)\\ =3\times \mathrm{Ik}\end{array}& \left(31\right)\end{array}$

[00168] Herein the first term on the right side of Equation (31) {Ic₃ cos(2πF₃t)+Ic₃ cos(2πF₃t−2π/3)+Ic₃ cos(2F₃t−4π/3)}=0. In other words, the first-rotor currents I₃I, I₃4, I₃7 do not appear in the detected value of the sensor 54. This allows the 0°-phase current component Ik of the second-rotor current to be detected.

[00169] In the same manner, the supply lines 114, 115, 116 to the coils D4, D5, D6 in the first stator 44 and to the coils E4, E5, E6 in the second stator 45 are collected and pass through the same current sensor 55. The supply lines 117118, 119 to the coils D7, D8, D9 in the first stator 44 and to the coils E7, E8, E9 of the second stator 45 are collected and pass through the same current sensor 56. In this manner, the 120°- and 240°-phase current components Il, Im of the second-rotor current are detected as a multiple of three.
Detected value of sensor 55=3×Ic₄ cos(2πF₄t−2π/3)=3×Il  (32)
Detected value of sensor 56=3×Ic₄ cos(2πF₄t−4π/3)=3×Im  (33)

[00172] Thus all the current components Ik, Il, Im of the second-rotor current are determined by three current sensors 54-56. The current sensor simultaneously detects the currents flowing in a set of three supply lines, such as (111,112,113), (111,114,117). In the set of three supply lines, current components, for example Ip, of the frequency F₃ flow in phase and current components, Ik, Il, Im, of the frequency F₄ flow with different phases from one another. The three current components of the frequency F₄ deviate at regular phase intervals of 120°. Thus, the current components of the frequency F₄ cancel out to zero in the set of supply lines.

[00173] The operation and effect of the second embodiment are the same as that described referring to the first embodiment.

[00174] When a current sensor which should detect only a current component at one frequency detects the current components at other frequencies, it is determined that the coil where a current component with the other frequency flows has become disconnected. For example, when a current component with a frequency F₄ is intermingled in a sensor which should only detect a current component with a frequency F₃, it is determined that the coil where a current component with a frequency F₄ flows has become disconnected.

[00175] This is described precisely as follows. In order to detect the current component Ip of the first-rotor current, the supply lines 111, 114, 117 to the coils D1, D4, D7 in the first stator 44 and to the coils E1, E4, E7 in the second stator 45 are collected and pass through the same current sensor 51. The fact that a current component with a frequency F₄ is detected by the current sensor 51 indicates that one of the coils E1, E4, E7 of the second stator 45 has become disconnected.

[00176] In this situation, the above equation takes the following form.
Detected value of sensor 51=3×Ic₃ cos(2πF₃t)+ΔI  (34)

• • [00178] Where ΔI is as follows.

[00179] When the coil E1 is disconnected:
ΔI=Ic₄ cos(2πF₄t−2π/3)+Ic₄ cos(2πF₄t−4π/3)  (35a)

[00181] When the coil E4 is disconnected:
ΔI=Ic₄ cos(2πF₄t)+Ic₄ cos(2πF₄t−4π/3)  (35b)

[00183] When the coil E7 is disconnected:
ΔI=Ic₄ cos(2πF₄t)+Ic₄ cos(2πF₄t−2π/3)  (35c)

[00185] ΔI in Equation (34) above is a function of the frequency F4. When the current characteristics after a d-q conversion of the detected value of the current sensor 51 are considered, the actual d-current and the actual q-current take an oscillating waveform when a disconnection in one of the coils E1, E4, E7 in the second stator 45 has occurred. When a disconnection in one of the coils E1, E4, E7 in the second stator 45 has not occurred, the actual d-current and the actual q-current display substantially fixed characteristics. Also, when a disconnection has occurred in any two of the coils E1, E4, E7 in the second stator 45, as described above, the actual d-current and the actual q-current take an oscillating waveform. Thus if an oscillation results in the actual d-current and the actual q-current obtained from the detection value of the current sensor 51, it is determined that a disconnection has occurred in one or two of the coils E1, E4, E7 in the second stator 45.

[00186] In the two embodiments above, in order to detect current components at a first frequency (in the first embodiment, F1 and in the second embodiment F₃), the supply lines are collected and passed through the same current sensor so that the phase of the current components of the first frequency (F₁, F₃) is the same and the current components of the second frequency (in the first embodiment F₂, in the second embodiment F₄) cancel out to a value of zero. Furthermore in order to detect current components at a second frequency (F₂, F₄), the supply lines are collected and passed through the same current sensor so that the phase of the current components of the second frequency (F₂, F₄) is the same and the current components of the first frequency (F₁, F₃) cancel out to a value of zero.

[00187] In the two embodiments above, the number of supply lines has been described taking a maximum number (four lines in the first embodiment and three lines in the second embodiment) as an example. However the invention is not limited in this regard.

[00188] For example, in the first embodiment, only two supply lines may be collected. To described this point in further detail, in order to detect the 0°-phase, current component Iu of the outer-rotor current, the supply lines 11, 14 to the coils C1, C4 or the supply lines 17, 20 to the coils C7, C10 are collected into a single set of two supply lines and pass through the same current sensor 31.

[00189] The detected values of the current sensor 31 at this time are as shown below.
Detected value of sensor 31=I1+I4=(I₁1+I₁4)+(I₂1+I₂4)  (36)
or
=I7+I10=(I₁7+I₁10)+(I₂7+I₂10)  (37)

[00193] Herein the initial phase angles α, β are set to a value of zero. When Equation (3) and Equation (4) are substituted into the above equation, the following equation is derived.
Detected value of sensor 31=2×Ic₁ cos(2πF₁t)+{Ic₂ cos(2πF₂t)+Ic₂ cos(2πF₂t−π)}=2×Ic₁ cos(2πF₁t)=2×Iu  (38)

[00195] Herein the right-side expressions Ic₂ cos(2πF₂t) and Ic₂ cos(2πF₂t−π) exactly cancel out and Ic₂ cos(2πF₂t)+Ic₂ cos(2πF₂t−π)=0. In other words, when detecting the composite current I1 and I4 or I7 and I10 together, the inner-rotor currents I₂1 and I₂4, or I₂7 and I₂10 do not appear in the detected value from the current sensor 31. Thus the detected value from the current sensor 31 coincides with the product of half the number of pole pairs of the current component Iu of the outer-rotor current. Half the number of pole pairs in this instance is two.

[00196] In the same manner, the supply lines 12 and 15 to the coils C2 and C5 or the supply lines, 18 and 21 to the coils C8 and C11 are collected and pass through the same current sensor 32. The supply lines 13 and 16 to the coils C3 and C6 or the supply lines 19 and 22 to the coils C9 and C12 are collected and pass through the same current sensor 33. In this manner, the 120°- and 240°-phase current components Iv, Iw of the outer-rotor current are detected as a multiple of two.

[heading-00197]  Detected value of sensor 32=2×Ic₁ cos(2πF₁t−2π/3)=2×Iv  (39)
Detected value of sensor 33=2×Ic₁ cos(2πF₁t−4π/3)=2×Iw  (40)

[00199] Thus all the current components Iu, Iv, Iw of the outer-rotor current can be determined by three current sensors 31-33. The detection of the inner-rotor current is performed in a like manner.

[00200] The advantages and disadvantages of using two collected supply lines in comparison to the first embodiment where a maximum number of four collected supply lines were used are as follows.

[00201] (i) When two supply lines are collected, the adverse effect of deviations in the inductance of the coils or the wiring increases. In contrast, when a maximum of four supply lines are collected, deviations in the inductance of the coils or wiring have little effect on the detected value of the current sensor 32. This is because, even when the deviation in two supply lines is large, the deviation in the remaining two supply lines can be small.

[00202] (ii) When a maximum of four supply lines are collected, the controller 8 is not required to make the detected value of the sensor 32 a multiple of the number of pole pairs. However when two collected supply lines are used, the controller 8 is required to double the detected value of the current sensor 32.

[00203] Although the embodiments of this invention have been described with respect to providing a current sensor in the supply line, the invention is not limited in this respect and it is possible to provide a sensor in proximity to the neutral point of the coils.

[00204] The entire contents of Japanese Patent Application P2001-207633 (filed Jul. 9, 2001) are incorporated herein by reference.

[00205] Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above.

[00206] Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.