Abstract:
A rotary electric machine for a vehicle includes a rotor, a stator and a rectifying device for current AC/DC conversion. The machine operates as a motor and a generator. The machine comprises a multi-phase windings, switching elements forming a rectifying device, and a controller for controlling a current path of the multi-phase windings by switching the switching elements on and off to perform two modes of operation. The switching elements are switched such that one end of each windings is connected to either a high electrical potential end or a low electrical potential end of the rectifying device and the other ends of the windings connected together to be the same electrical potential are connected to either the high electrical potential end or the low electrical potential end in the rectifying device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to Japanese Patent Application NO. 2007-225748 filed on Aug. 31, 2007, the contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a rotary electric machine mounted on a vehicle, and in particular, to the rotary electric machine having a rotor and a stator equipped with multi-phase windings for making the machine function as a motor and a generator. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, some vehicles have a function for stopping the idle rotation (i.e., idling) of the engine for saving consumption of fuel. In such vehicles, the engine is frequently turned off every time and started up every time the vehicle stops. Because the stop and start-up of the engine is repeated, it is desired that a generator mounted on the vehicle be motor-driven and serves as a starter which has a problem regarding the life of brushes incorporated in the starter. In these vehicles, important parameters necessary when quickly starting the engine are a start-up torque having no rotation and a predetermined torque at which the rotation increases to a value equivalent to the idle rotation. 
         [0006]    It is desired that fluctuations in the engine-rotation can be stabilized by supplying torque from the generator to the engine. Thus, the generator is required to be motor-driven while the engine rotation can become unstable due to unexpected disturbance of torque of the engine. In these vehicles, motor torque is also required to be generated at least at the level of idle rotation. 
         [0007]    In general, the vehicle generator is designed to supply required power at an idle rotation of about 1500 rpm. When the vehicle generator is designed in this way, the revolution speed at which extraction of a generated power current becomes possible is about 1000 rpm. 
         [0008]    When the vehicle generator is motor-driven, a voltage suitable for charging the battery is generated at a revolution speed of 1000 rpm. Therefore, electric current cannot be sent from the battery during motor operation. Hence, a sufficient torque cannot be generated at the revolution speed. 
         [0009]    As shown in  FIG. 1 , the torque decreases linearly from a non-rotation start-up torque to a power generation starting revolution speed. Although some torque can be extracted through weakening current-flowing in the field winding of the generator, the torque is not sufficient for the purpose described above. 
         [0010]    Characteristics of a synchronous rotary machine such as that above are determined by an inductance of a stator, specifically, the number of windings in a stator winding. As shown in  FIG. 2 , in power generation characteristics, the minimum revolution speed required for initiating the power generation changes depending on the amount of the inductance (the number of windings), and torque and revolution characteristics during motor-driving also change in accompaniment. 
         [0011]    In a vehicle rotary machine having both power generation and engine driving functions, it is difficult to actualize the characteristics required during power generation and the characteristics required for torque of the engine with the same inductance. A conflicting request is made in that, when the power generation characteristics are given priority, motor characteristics become a state in which the drive torque is insufficient. When the motor characteristics are given priority, the power generation output during idle rotation becomes insufficient. 
         [0012]    As a conventional technology responding to such requests, a series-parallel conversion rotary electric machine in Japanese Patent Laid-open Publication No. Heisei 4-88900 is known. The series-parallel conversion rotary electric machine provides two sets of stator windings and changes impedance by switching the stator windings between serial and parallel. In another conventional technology, a rotary electric machine is known in which switching elements are disposed at a neutral point and between a high potential and a low potential of a Y-connected three-phase winding in the rotary electric machine. When an abnormality, such as disconnection, occurs in the three-phase winding, the rotary electric machine uses the neutral point in place of the winding of the phase at which the abnormality has occurred. 
         [0013]    In the series-parallel conversion rotary electrical machine disclosed in Japanese Patent Laid-open Publication No. Heisei 4-88900, a plurality of sets of multi-phase windings are required to be mounted in the stator. Problems occur in that a configuration of the stator becomes complicated and cost rises. A large number of switching elements for switching the winding between serial and parallel is additionally required. For example, compared to six rectifying elements ordinarily required, nine switching elements are additionally required, thereby also contributing to the increase in cost. 
         [0014]    In addition, the rotary electric device disclosed in Japanese Patent Laid-open Publication No. 2007-99066 is a technology used only during motor-driving and in response to an abnormal situation, and does not meet the above-described requirements. A conventional three-phase winding is driven by only a two-phase winding and three phases are imitated by use of the neutral point. Problems occur such as the rotation not being smooth. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention has been achieved in light of the above-described issues. An object of the present invention is to provide a vehicle rotary electric machine that can enable size reduction, high output, and high efficiency during power generation and high torque during motor-driving at a low cost. 
         [0016]    To solve the above-described issues, the vehicle rotary electric machine includes a rotor, a stator and a rectifying device that converts current between an alternating current and a direct current in the rotary electric machine. This vehicle rotary electric machine operates as a motor and a generator on the vehicle, comprising a multi-phase windings wounded in the stator; a plurality of switching elements electrically connected to the multi-phase windings to form the rectifying device; and a controller for controlling current path of the multi-phase windings by switching the switching elements on and off to perform two modes of rectifying operation, the switching elements are switched such that one end of each windings is connected to either a high electrical potential end or a low electrical potential end of the rectifying device and the other ends of the windings that are connected together at the same electrical potential are connected to either the high electrical potential end or the low electrical potential end in the rectifying device. 
         [0017]    When the multi-phase winding is connected by Y-connection, an electrical current always flows to two phases when ordinary rectification is performed. The inductance becomes a geometric sum. In the present invention, the neutral point rectification mode is provided in which rectification is performed through use of a switch corresponding to the neutral point on an electric potential side differing from the high-side (i.e., higher electrical potential side) and low-side (i.e., lower electrical potential side) winding end switching elements. Therefore, in the neutral point rectification mode, the electrical current enters and exits from the neutral point, and only flows through the winding of one phase. Therefore, the inductance is only that of a winding of a single phase. In other words, a low-inductance winding can be achieved. In the present invention, the control device can arbitrarily switch between two control modes. As a result, the control device can change the inductance using the same three-phase winding. Therefore, only a single set of three-phase windings is required. Size reduction, high output, and high efficiency can be obtained during power generation and high torque can be actualized during motor-driving (motor operation) at a low cost. Because characteristics can be arbitrarily changed by the control mode being switched, optimal power generation characteristics or motor torque characteristics can be achieved at any given time. 
         [0018]    The above-described control device switches between the multi-phase full-wave rectification mode and the neutral point rectification mode depending on a revolution speed of the rotor. As a result of the control mode being switched depending on the revolution speed, a control program can be simplified. In addition, because the power generation characteristics and the motor torque characteristics are dependent on the revolution speed, more favorable characteristics can be achieved. 
         [0019]    The above-described control device switches to the multi-phase full-wave rectification mode when the revolution speed is slower than a predetermined revolution speed and to the neutral point rectification mode when the revolution speed is faster than the predetermined revolution speed. As a result, during power generation, inductance of the stator can be increased to enhance power generating capability when the revolution speed is slower than the predetermined revolution speed. On the other hand, when the revolution speed is faster than the predetermined revolution speed, the inductance can be reduced. Reaction can be reduced and a high output can be achieved. During motor-driving, a high torque can be achieved to reduce the inductance when the revolution speed is faster than the predetermined revolution speed. 
         [0020]    The above-described control device switches between the multi-phase full-wave rectification mode and the neutral point rectification mode depending on whether operation is performed as the motor or as the generator. In a conventional configuration, it is difficult to achieve favorable characteristics during power generation and motor-driving. However, the inductance can be equivalently changed in the present invention. Therefore, favorable characteristics can be achieved both during power generation and during motor-driving. 
         [0021]    The above-described rectification control device switches to the multi-phase full-wave rectification mode when operation is performed as the generator and to the neutral point rectification mode when operation is performed as the motor. As a result, during power generation, a high output can be achieved even at a low-speed revolution. During motor-driving, the inductance can be equivalently reduced. Therefore, simultaneous power generation and motor-driving, which was difficult in a vehicle generator, can be obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the accompanying drawings: 
           [0023]      FIG. 1  is a diagram showing characteristics of a conventional vehicle generator 
           [0024]      FIG. 2  is a diagram showing a relationship between inductance and power generation in the conventional vehicle generator. 
           [0025]      FIG. 3  is a connection wiring diagram showing an overall configuration of a vehicle rotary electric machine according to an embodiment of the present invention; 
           [0026]      FIG. 4  is a diagram showing an operating state of each switching element in neutral point control mode; 
           [0027]      FIG. 5  is a diagram showing an operating state of each switching element in multi-phase full-wave rectification control mode; 
           [0028]      FIG. 6  is a diagram showing an operating state of each switching element in neutral point rectifying mode of a variation example corresponding to half-wave rectification; 
           [0029]      FIG. 7  is a diagram showing an operating state of each switching element in neutral point rectifying mode in another variation example corresponding to half-wave rectification; 
           [0030]      FIG. 8  is a diagram showing an overview of multi-phase full-wave rectification mode; and 
           [0031]      FIG. 9  is a diagram showing an overview of neutral point rectification mode. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    A vehicle rotary electric machine according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings  FIGS. 3 to 9 . 
         [0033]      FIG. 3  is a connection wiring diagram showing an overall configuration of a vehicle rotary electric machine according to an embodiment. As shown in  FIG. 3 , the rotary electric machine  100  according to the present embodiment includes a three-phase winding  1 , a field winding  2 , a rectifying device  3 , and a controlling device S. The three-phase winding  1  serves as a multi-phase winding included in a stator. The field winding  2  is included in a rotor. The three-phase winding  1  is wound around a stator core (not shown) at a pitch of 180 electrical degrees equivalent to an amount for a single magnetic pole of the rotor in which the field winding  2  is provided. Each phase winding is connected by a Y-connection. Three output terminals (winding terminals) of each phase of the three-phase winding  1  and a neutral point N are connected to the rectifying device  3 . 
         [0034]    The rectifying device  3  includes eight switching elements including a transistor and a diode connected between a source and a drain of the transistor. Specifically, three high-side (i.e., higher electrical potential side) winding-end switching elements  311  to  313  are disposed between winding ends of each phase of the three-phase winding  1  and a high potential end  30 . Three low-side (i.e., lower electrical potential side) winding-end switching elements  314  to  316  are disposed between the winding ends of each phase and a low potential end  32 . As a result, a three-phase full-wave rectification bridge  31  is configured. At the same time, an output terminal  111  is also drawn from the neutral point N. A high-side neutral point switching element  317  is disposed between the output terminal  111  and the high potential end  30 . A low-side neutral point switching element  318  is disposed between the output terminal  111  and the low potential end  32 . According to the present embodiment, a low-loss metal-oxide semiconductor field-effect transistor (MOSFET) is used in each switching element. In each switching element, the controlling device  5  serving as a rectification controlling section generates a control signal to be inputted into a gate, and conduction control (e.g., intermittent control) is performed. 
         [0035]    The rectifying device  3  is connected to an external battery  20  and an electrical load  91 . When the rotary electric machine  100  performs a power generating operation, a charging current and an operating current are supplied to the battery  20  and the electrical load  91  from the rectifying device  3 . On the other hand, when the rotary electric machine  100  performs a motor operation, a motor-driving current required for the motor operation is supplied to the rectifying device  3  from the battery  20 . 
         [0036]    The controlling device  5  is respectively connected to an external electronic controlling unit (ECU)  6 , a position sensor  52 , and a voltage sensor  53  (in  FIG. 3 , a connection line introducing a terminal voltage from the battery  5  to the controlling device  5  is simply shown as the voltage sensor  53 ). The position sensor  52  detects the rotation position of the rotor. The voltage sensor  53  detects the terminal voltage of the battery  20 . Based on signals inputted from the ECU  6 , the position sensor  52 , and the voltage sensor  53 , the controlling device  5  decides the control mode, inputs a control signal into each switching element, and supplies the field winding  2  with a field current. 
         [0037]    According to the present embodiment, the rotary electric machine  100  can be operated in two types of control modes. One is multi-phase full-wave rectification mode in which the rectifying device  3  operates with only the high-side winding-end switching elements  311  to  313  and the low-side winding-end switching elements  314  to  316 . The other is neutral point rectification mode in which the rectifying device  3  operates including the low-side neutral point switching element  318  or the high-side neutral point switching element  317 . Either the high-side winding-end switching elements  311  to  313  or the low-side winding-end switching elements  314  to  316  are selected as a different electrical potential side from the neutral point switching elements  318  or  317 . 
         [0000]    Detailed operations in each control mode will be described hereafter. 
         [0038]    A signal indicating whether to operate the rotary electric machine  100  as the generator to generate power or as the motor is sent from the ECU  6  to the controlling device  5 . When generating power, the rotary electric machine  100  forms an NS (North and South) pole by sending an electric current to the field winding  2  in the rotor. As a result of rotating the NS pole on an inner circumferential side of the stator, the rotary electric machine  100  generates an alternating current in the three-phase winding  1  by electromagnetic induction. The rotary electric machine  100  converts the alternating current to a direct current using the rectifying device  3  and supplies the output to an external destination. When motor-driving, the rotary electric machine  100  forms an NS pole by sending an electric current to the field winding  2  in the rotor. The rotary electric machine  100  also converts a direct current applied from the battery  20  to an alternating current using the rectifying device  3  and sends the current to the three-phase winding  1 . The rotary electric machine  100  creates a rotating field and rotates the rotor. 
         [0039]    The rotary electric machine  100  according to the present embodiment is configured as described above. Next, operations thereof will be described.  FIG. 4  is a diagram showing an operating state of each switching element in neutral point control mode.  FIG. 5  is a diagram showing an operating state of each switching element in multi-phase full-wave rectification control mode. In the diagrams, G 1  to G 3  indicate control signals inputted into respective gates of the high-side winding-end switching elements  311  to  313 . G 4  to G 6  indicate control signals inputted into respective gates of the low-side winding-end switching elements  314  to  316 . G 7  indicates a control signal inputted into a gate of the high-side neutral point switching element  317 . G 8  indicates a control signal inputted into a gate of the low-side neutral point switching element  318 . When the control signals are at high level (ON), the corresponding switching elements are set to the ON state. When the control signals are set to the low level (OFF), the corresponding switching elements are controlled at an OFF state. In  FIGS. 4 and 5  and  FIGS. 6 and 7  described hereafter, the horizontal axis is a temporal axis. 
         [0040]    As shown in  FIG. 5 , in the multi-phase full-wave rectification mode, conduction of each switching element is controlled in a manner similar to common full-wave rectification. The high-side neutral point element  317  and the low-side neutral point element  318  are normally turned off and are not used. 
         [0041]    At the same time, as shown in  FIG. 4 , in the neutral point control mode, each high-side winding-end switching element  311  to  313  and each low-side winding-end switching element  314  to  316  are controlled to have a phase difference of 120 electrical degrees to each other. A conduction interval is 60 degrees and is set such that other phases do not temporally overlap. 
         [0042]    The high-side neutral point switching element  317  and the low-side neutral point switching element  318  are configured such as to switch between the ON state and the OFF state mutually exclusive of each other at a 60-degree interval. 
         [0043]    The winding end switching elements and the neutral point switching elements are conduction-controlled such that one pair of switching elements with opposite polarity are always simultaneously in the ON state. A current path is formed such that an electrical current is outputted from or inputted into the neutral point N. When any of the high-side winding-end switching elements  311  to  313  is turned ON, the low-side neutral point switching element  318  is turned ON. On the other hand, when any one of the low-side winding-end switching elements  314  to  316  is turned ON, the high-side neutral point switching element  317  is turned on. The switching elements are controlled such that different electric potential end sides are always turned ON. 
         [0044]    In the multi-phase full-wave rectification mode shown in  FIG. 5 , only the winding ends of the three-phase winding  1  are connected to the rectifying device  3  (because both the high-side neutral point switching element  317  and the low-side neutral point switching element  318  are normally in the OFF state). Therefore, as shown in an overview in  FIG. 8 , an electrical current always flows through two phases in the three-phase winding  1  (the current path is indicated by an arrow in  FIG. 8 ). As a result, inductance of the three-phase winding  1  increases evenly. In theory, the increase is by √3-fold (about 1.7 folds) of the inductance of the winding of a single phase. On the other hand, in the neutral point rectification mode shown in  FIG. 4 , the rectifying device  3  is connected to both the winding ends of the three-phase winding  1  and the neutral point N. The electrical current is inputted and outputted through all switching elements. As shown in an overview in  FIG. 9 , control is performed such that the electrical current only flows through one phase in the three-phase winding  1  (the current path is indicated by an arrow in  FIG. 9 ). Therefore, the inductance of the overall three-phase winding  1  becomes small. Excitation can be weakened without field weakening. Therefore, through selective use of the multi-phase full-wave rectification mode and the neutral point control mode, an optimal inductance can be selected in various operating modes, such as power generation and motor-driving, and high speed and low speed rotation. 
         [0045]    For example, it is possible that the controlling device  5  switches between the multi-phase full-wave rectification mode and the neutral point rectification mode depending on a revolution speed of the rotor. As a result of the control mode being switched depending on the revolution speed, a control program can be simplified. Because power generation characteristics and motor torque characteristics are dependent on the revolution speed, more favorable characteristics can be achieved. 
         [0046]    Also, it is possible that the controlling device  5  switches to the multi-phase full-wave rectification mode when the revolution speed is slower than a predetermined revolution speed, and switches to the neutral point rectification mode when the revolution speed is faster than a predetermined revolution speed. As a result, during power generation, inductance of the stator can be increased to enhance power generating capability when the revolution speed is slower than the predetermined revolution speed. On the other hand, when the revolution speed is faster than the predetermined revolution speed, the inductance can be reduced. Reaction can be reduced and high output can be achieved. During motor-driving, a high torque can be achieved by reducing the inductance when the revolution speed is faster than the predetermined revolution speed. 
         [0047]    It is possible that the controlling device  5  switches between the multi-phase full-wave rectification mode and the neutral point rectification mode depending on whether the rotary electric machine  100  operates as the motor or the generator. In a conventional configuration, it is difficult to achieve favorable characteristics during power generation and motor-driving. However, the inductance can be equivalently changed in the present invention. Therefore, favorable characteristics can be achieved both during power generation and during motor-driving. Specifically, switching the controlling device  5  to the multi-phase full-wave rectification mode when the rotary electric machine  100  operates as the generator and switching to the neutral point rectification mode when the rotary electric machine  100  operates as the motor can be considered. As a result, during power generation, a high output can be achieved even at a low-speed revolution. During motor-driving, the inductance can be equivalently reduced. Therefore, simultaneous power generation and motor-driving, which was difficult in a vehicle generator, can be obtained. 
         [0048]    In this way, in the rotary electric machine  100  of the present invention, because the neutral point rectification mode is provided in which rectification is performed using the high-side winding-end switching elements  311  to  313  or the low-side winding-end switching elements  314  to  316  and the neutral point switching element  318  or  317  with the differing electric potential. In this control mode, the electrical current enters and exits from the neutral point and only flows through the winding of one phase. Therefore, the inductance is only that of an amount for a winding of a single phase. In other words, a low-inductance winding can be achieved. In the rotary electric machine  100  of the present invention, the controlling device  5  can arbitrarily switch between two control modes. As a result, the controlling device  5  can change the inductance using the same three-phase winding  1 . Therefore, only a single set of three-phase winding  1  is required. Size reduction, high output, and high efficiency can be actualized during power generation and high torque can be actualized during motor-driving at a low cost. Because characteristics can be arbitrarily changed by the control mode being switched, optimal power generation characteristics or motor torque characteristics can be achieved at any given time. 
         [0049]    In the neutral point rectification mode shown in  FIG. 4 , a full-wave rectification is performed in which the high-side winding-end switching elements  311  to  313  and the low-side winding-end switching elements  314  to  316  are all periodically switched on and off. However, neutral point rectification mode corresponding to a half-wave rectification can also be used. 
         [0050]      FIG. 6  is a diagram of an operating state of each switching element in the neutral point rectification mode of a variation example corresponding to the half-wave rectification. In the neutral point rectification mode shown in  FIG. 6 , the high-side neutral switching element  317  is normally ON and the low-side winding-end switching elements  314  to  316  of a differing electric potential are s conduction-controlled. As a result of the rectifying device  3  performing a half-wave rectification operation in this way, the inductance of the three-phase winding  1  in the neutral point rectification mode can be further reduced. 
         [0051]      FIG. 7  is a diagram of an operating state of each switching element in neutral point rectification mode of another variation example corresponding to the half-wave rectification. In the neutral point rectification mode shown in  FIG. 7 , the low-side neutral point switching element  318  is normally ON and the high-side winding-end switching elements  311  to  313  of a differing electric potential are conduction-controlled. In this instance as well, the inductance of the three-phase winding  1  in the neutral point rectification mode can be further reduced. In the neutral point rectification modes shown in  FIG. 6  and  FIG. 7 , a conduction interval of each winding end switch is 60 degrees. However, the conduction interval can also be 120 degrees. 
         [0052]    The present invention is not limited to the embodiment described above. Various medications can be made within a scope of the summary of the present invention. For example, according to the above-described embodiment, the rotary electric machine  100  including the three-phase winding  1  has been described. However, the present invention can be applied to a rotary electric machine including a multi-phase winding other than the three-phase winding.