Abstract:
A method of generating and controlling power for an alternating current (AC) motor by means of at least one controlled permanent magnet machine (PMM) with a permanent magnet (PM) rotor and a stator with a magnetic flux diverter circuit for controlling the output of the PMM, comprises the steps of: rotating the PM rotor at a velocity sufficient to develop a high frequency alternating current (HFAC) power output from the stator; transforming the HFAC output to produce a variable low frequency alternating current (AC) motor control output for the motor; sensing desired motor control parameters; generating a control signal responsive to the sensed parameters; and applying the control signal to the magnetic flux diverter circuit to control the motor control output.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to motor drive systems for alternating current (AC) motors, and more particularly to AC motor drive systems employing magnetic flux control. 
       BACKGROUND OF THE INVENTION  
       [0002]    It is of great importance to minimise the size and weight of motor drive systems for mobile applications. Such motor drive systems generally derive electrical power for their operation from a mechanical source that comprises a prime mover, such as an engine. An electrical generator converts mechanical power from the prime mover into electrical power. Most commonly, the motor drive system utilises existing AC power and converts it variable frequency AC to drive a multiphase AC motor. The multiphase AC has a frequency or range of frequencies, such as zero to approximately 400 Hz, which is sufficient to drive the AC motor through a desired range of speeds. 
         [0003]    The electrical generator generally has a multiphase AC output at a relatively low fixed fundamental frequency, generally about 50, 60, or 400 Hz, or a variable frequency that covers the range of approximately 360 to 800 Hz, which requires conversion in the motor drive system from generator multiphase AC output to the range of frequencies sufficient to drive the AC motor at the desired range of speeds. Such a motor drive system requires high power electronics, which add size, weight and cost to the system. It would be desirable to use low power electronics to vary the output of the generator itself to produce the necessary range of frequencies sufficient to drive the AC motor at the desired range of speeds. 
       SUMMARY OF THE INVENTION  
       [0004]    The invention generally comprises a method of generating and controlling power for an alternating current (AC) motor by means of at least one controlled permanent magnet machine (PMM) with a permanent magnet (PM) rotor and a stator with a magnetic flux diverter circuit for controlling the output of the PMM, comprising the steps of: rotating the PM rotor at a velocity sufficient to develop a high frequency alternating current (HFAC) power output from the stator; transforming the HFAC output to produce a variable low frequency alternating current (AC) motor control output for the motor; sensing desired motor control parameters; generating a control signal responsive to the sensed parameters; and applying the control signal to the magnetic flux diverter circuit to control the motor control output. 
     
    
     
       DESCRIPTION OF THE DRAWINGS  
         [0005]      FIG. 1  is a schematic diagram of a motor drive system according to a first possible embodiment of the invention. 
           [0006]      FIG. 2  are schematic diagrams of three possible bi-directional switch arrangements for the motor drive system shown in  FIG. 1 . 
           [0007]      FIG. 3  is a schematic diagram of a motor controller according to a possible embodiment of the invention for the motor drive system shown in  FIG. 1 . 
           [0008]      FIG. 4  is a schematic diagram of a motor drive system according to a second possible embodiment of the invention. 
           [0009]      FIG. 5  is a schematic diagram of a motor controller according to a possible embodiment of the invention for the motor drive system shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]      FIG. 1  is a schematic diagram of a motor drive system  2  according to a first possible embodiment of the invention. The motor drive system  2  comprises a prime mover  4 , such as a gas turbine engine, that couples to at least one high frequency alternating current (HFAC) generator module  6  by means of a prime mover drive shaft  8 . Each HFAC generator module  6  includes a variable low frequency alternating current (AC) motor control output that an AC motor  10  receives by way of a corresponding generator module output line  12 . For this embodiment of the motor drive system  2 , an AC motor  10  with N phases will receive N motor control outputs, each representing a different phase of the AC motor  10 , from N different generator modules  6  by way of corresponding generator module output lines  12 . Typically the AC motor  10  will have three phases, and therefore receive three phases of motor control outputs from three respective generator modules  6  by way of three respective generator module output lines  12 , as shown in  FIG. 1 . Alternatively, the AC motor  10  may have two or more than three phases. 
         [0011]    Each generator module  6  comprises a single phase controlled permanent magnet machine (PMM)  14  that serves as a HFAC generator, such as of the type described in co-pending patent application U.S. Ser. No. 12/355,864 to Gieras et al., owned by the assignee of this application and hereby incorporated by reference. Each PMM  14  has a permanent magnet (PM) rotor  16  and a stator  18  with a magnetic flux diverter circuit  20 . The prime mover  4  rotates the PM rotor  16  by way of the prime mover drive shaft  8  at a velocity sufficient to develop a HFAC current in the stator  18 . The stator  18  has a centre-tapped single phase output with the centre tap grounded to provide a balanced single phase HFAC output with respect to ground on stator output lines  22 . A bi-directional switching circuit  24  receives the balanced single phase HFAC output on the stator output lines  22  and transforms it to produce the motor control output of the generator module  6  on its respective generator module output line  12 . A current sensor  26  may monitor the current level of the motor control output on the generator module output line  12  and generate a respective current level output signal on a current sensor output line  28  that is representative of the sensed current level. 
         [0012]    The AC motor  10  has a motor drive shaft  30  that revolves in proportion to the frequency of the variable low frequency motor control outputs that it receives on the generator module output lines  12 . A position sensor  32  may sense the angular position of the motor drive shaft  30  and generate a respective motor position signal on a position sensor output line  34  that is representative of the sensed motor drive shaft position. 
         [0013]    A motor controller  36  receives motor control parameters comprising the current level output signal on each current sensor output line  28  and the motor position signal on the position sensor output line  34 , as well as a speed reference signal on a speed signal line  38  and a direct current reference signal Id_ref on a direct current reference signal line  40 , to generate a control signal for each generator module  6  on a respective control signal line  42  that has a fundamental frequency corresponding to the desired frequency of the variable low frequency AC motor control output on its respective generator module output line  12 . 
         [0014]    An absolute value output circuit  44  within each generator module  6  receives its respective control signal by way of its respective control signal line  42  and converts it to an absolute value signal on an absolute value signal line  46 . A summer  48  receives the absolute value signal on the absolute value signal line  46  and a magnetic flux diverter circuit current signal on a magnetic flux diverter circuit current signal line  50  by way of an inverted input to generate a summer difference signal on a summer difference signal line  52 . A magnetic flux diverter circuit current regulator  54  receives the summer difference signal on the summer difference signal line  52  to generate a magnetic flux diverter circuit current drive signal on a magnetic flux diverter circuit current drive signal line  56 . 
         [0015]    An H-bridge  58  receives the magnetic flux diverter circuit current drive signal on a magnetic flux diverter circuit current drive signal line  56  to produce a magnetic flux diverter circuit current on H-bridge output lines  60 . The magnetic flux diverter circuit  20  receives the magnetic flux diverter circuit current on the H-bridge output lines  60  to control the level of the balanced single phase HFAC output on the stator output lines  22 . A magnetic flux diverter circuit current sensor  62  senses the level of current passing through the H-bridge output lines  60  and generates the a magnetic flux diverter circuit current signal on the magnetic flux diverter circuit current signal line  50  to be representative of the sensed current level. 
         [0016]    A zero crossing detector circuit  64  senses the zero crossings of the control signal on the control signal line  42  and generates a zero crossing output signal on a zero crossing output signal line  66  and an inverted zero crossing output signal on an inverted zero crossing output signal line  68 . A first bi-directional gate drive circuit  70  in the bi-directional switching circuit  24  receives the zero crossing output signal by way of the zero crossing output signal line  66  and generates a respective first gate drive signal to drive a respective first bidirectional switch  72  and control current flow between one of the stator output lines  22  and the generator module output line  12 . A second bi-directional gate drive circuit  74  receives the inverted zero crossing output signal by way of the inverted zero crossing output signal line  68  and generates a respective second gate drive signal to drive a respective second bi-directional switch  76  and control current flow between the other one of the stator output lines  22  and the generator module output line  12 .  FIG. 2  are schematic diagrams of three possible bi-directional switch arrangements for the bi-directional switches  72  and  76  shown in  FIG. 1 . 
         [0017]    Since each control signal is AC, with a fundamental frequency that represents the desired frequency of the variable low frequency AC motor control output of its respective generator module  6  on its respective generator module output line  12 , the action of the generator module  6  is that of an electromechanical amplifier, wherein the control signal on the control signal line  42  may be of low power to control the high motor control output on the generator module output line  12 . Another way of looking at the action is that the relatively low power control signal on the control signal line  42  by means of the magnetic flux diverter circuit  20  modulates the HFAC output on the stator output lines  22  and the bi-directional switching circuit  24  demodulates the HFAC output on the stator output lines  22  to produce the high motor control output on the generator module output line  12  with the same frequency as its respective control signal on the control signal line  42 . 
         [0018]      FIG. 3  is a schematic diagram of the motor controller  36  according to a possible embodiment of the invention for the motor drive system  2  shown in  FIG. 1 . A speed estimator circuit  78  receives the motor position signal on the position sensor output line  34  and generates a respective motor speed signal on a speed estimator output line  80 . A summer  82  receives the speed reference signal on the speed signal line  38  and the motor speed signal on the speed estimator output line  80  by way of an inverted input to generate a respective summer difference signal on a summer output line  84 . A motor speed controller circuit  86  receives the summer difference signal on the summer output line  84  and generates a respective motor quadrature reference current signal Iq_ref on a speed controller circuit output line  88 . 
         [0019]    A Park&#39;s transformation circuit  90  receives the current level output signal from the current sensor  26  for each generator module  6  by way of the current sensor output lines  28  and the motor position signal on the position sensor output line  34  to generate a respective motor quadrature current feedback signal Iq_fdbk on a quadrature current feedback line  92  and a respective motor direct current feedback signal Id_fdbk on a direct current feedback line  94 . A summer  96  receives the motor quadrature reference current signal Iq_ref on the speed controller circuit output line  88  and the motor quadrature current feedback signal Iq_fdbk on the quadrature current feedback line  92  by way of an inverted input to generate a summer difference signal on a summer output line  98 . A proportional plus integral (PI) current regulator  100  receives the summer difference signal on the summer output line  98  to generate a respective quadrature voltage control signal Vq_ref on a PI controller output line  102 . 
         [0020]    A summer  104  receives the direct current reference signal Id_ref on the direct current reference signal line  40  and the motor direct current feedback signal Id_fdbk on the direct current feedback line  94  by way of an inverted input to generate a direct electrical potential difference control signal on a summer output line  106 . A PI current regulator  108  receives the summer difference signal on the summer output line  106  to generate a respective direct voltage control signal Vd_ref on a PI controller output line  110 . An inverse Park&#39;s transformation circuit receives the quadrature voltage control signal Vq_ref on the PI controller output line  102 , the direct voltage control signal Vd_ref on a PI controller output line  110  and the motor position signal on the position sensor output line  34  to generate the control signal for each generator module  6  on the respective control signal lines  42 . 
         [0021]      FIG. 4  is a schematic diagram of the motor drive system  2  according to a second possible embodiment of the invention. Similar to the first embodiment, the motor drive system  2  comprises a prime mover  4 , but it couples to a single generator module  114  by way of the prime mover drive shaft  8 . For this embodiment of the motor drive system  2 , the motor drive system  2  will operate the AC motor  10  with N phases by means of the single generator module  114 . 
         [0022]    The single generator module  114  comprises the PMM  14  as described in connection with the generator module  6 . It has the same PM rotor  16  and the stator  18  with the magnetic flux diverter circuit  20 . Likewise, the prime mover  4  rotates the PM rotor  16  by way of the prime mover drive shaft  8  at a velocity sufficient to develop a HFAC current in the stator  18 . The stator  18  has a centre-tapped single phase output with the centre tap grounded to provide a balanced single phase HFAC output with respect to ground on stator output lines  22 . Unlike the generator module  6 , the generator module  114  has an electrical potential difference sensor to sense the level of electrical potential difference present on the stator output lines  22 , and it generates an electrical potential difference signal representative of the measured level on an electrical potential difference sensor output line  118 . 
         [0023]    Unlike the generator module  6 , the generator module  114  outputs the balanced single phase HFAC output on stator output lines  22  to an N phase cycloconverter  120 . The N phase cycloconverter  120  has N of the bidirectional switching circuits  24  to transform the balanced single phase HFAC output on stator output lines  22  to N variable low frequency AC motor control outputs on N cycloconverter output lines  122 . Typically the motor  10  and the cycloconverter  120  will have three phases, and therefore three respective cycloconverter output lines  122 . Alternatively, the motor  10  and the cycloconverter  120  may have two or more than three phases. Much the same as the first embodiment of the motor drive system  2 , the current sensors  26  sense the level of current that the cycloconverter  120  supplies to each phase of the motor  10  and they generate respective current level output signals on their respective current sensor output lines  28 . 
         [0024]    A motor controller  124  receives the current level output signals on their respective current sensor output lines  28 , the electrical potential difference signal on the electrical potential difference sensor output line  118  and the motor position signal on the position sensor output line  34 , as well as the speed reference signal on the speed signal line  38 , to generate a generator module control signal on a generator module control signal line  126  and for each bidirectional switching circuit  24  in the cycloconverter  120  a high side gate drive control signal on a respective high side gate drive control line  128  and a low side gate drive control signal on a respective low side gate drive control line  130 . 
         [0025]    The summer  48  in the generator module  114  receives the generator module control signal on the generator module control signal line  126  and subtracts it from the magnetic flux diverter circuit current signal on the magnetic flux diverter circuit current signal line  50  to control the magnetic flux diverter circuit current on the H-bridge output lines  60  to in turn control the level of the balanced single phase HFAC output on the stator output lines  22  much the same as described for the first embodiment of the motor drive system  2 . However, in this case the generator module control signal on the generator module control signal line  126  does not have a variable low frequency AC component. Instead, the cycloconverter  120  generates the necessary variable low frequency AC fundamental of the variable low frequency AC motor control outputs on the cycloconverter output lines  122  in response to the high side gate drive control signals on their respective high side gate drive control lines  128  and the low side gate drive control signals on their respective low side gate drive control lines  130 . 
         [0026]      FIG. 5  is a schematic diagram of the motor controller  124  according to a possible embodiment of the invention for the motor drive system  2  according to the second embodiment shown in  FIG. 4 . The speed estimator circuit  78  in the motor controller  124  receives the motor position signal on the position sensor output line  34  and generates a respective motor speed signal on the speed estimator output line  80 . The summer  82  receives the speed reference signal on the speed signal line  38  and the motor speed signal on the speed estimator output line  80  by way of an inverted input to generate a respective summer difference signal on the summer output line  84 . The motor speed controller circuit  86  receives the summer difference signal on the summer output line  84  and generates a respective motor average reference current signal on the speed controller circuit output line  88 . 
         [0027]    An N phase signal rectifier  132 , shown as a three phase rectifier in  FIG. 4 , receives the current level output signal from the current sensor  26  for each of the cycloconverter output lines  122  and generates a respective motor average current feedback signal on a rectifier output line  134 . The summer  96  receives the motor average reference current signal on the speed controller circuit output line  88  and the motor average current feedback signal on the rectifier output line  134  by way of an inverted input to generate a summer difference signal on the summer output line  98 . The proportional plus integral (PI) current regulator  100  receives the summer difference signal on the summer output line  98  to generate the generator module control signal on the generator module control signal line  126 . 
         [0028]    An N phase sine look-up table circuit  136 , shown as a three phase sine look-up table circuit  136  in  FIG. 5 , receives the motor position signal on the position sensor output line  34  and generates respective sine value signals for each phase of the motor  10  on look-up table output lines  138 . N multipliers  140 , shown as three multipliers  140  in  FIG. 5 , each receive a respective one of the sine value signals on a respective one of the look-up table output lines  138  and the motor average reference current signal on the speed controller circuit output line  88  to generate a respective motor current reference signal for its respective phase of the motor  10  on a respective multiplier output line  142 . 
         [0029]    A hysteresis current controller  144  receives the motor current reference signal for each phase of the motor  10  on the multiplier output lines  142  and the current level output signal from the current sensor  26  for each of the cycloconverter output lines  122  to generate a respective hysteresis control output signal for each phase of the motor  10  on a respective hysteresis controller output line  146 . As shown in  FIG. 4 , the hysteresis controller  144  may comprise a summer  148  coupled to a hysteresis circuit  150  by a summer output line  152  for each phase of the motor  10 . 
         [0030]    A hysteresis circuit  154  receives the electrical potential difference signal on the electrical potential difference sensor output line  118  and generates a respective hysteresis synchronisation signal on a hysteresis circuit output line  156 . A signal steering block  158 , such as described in co-pending patent application U.S. Ser. No. 12/435,534 to Nguyen et al., owned by the assignee and hereby incorporated by reference, receives the respective hysteresis control output signals on the respective hysteresis controller output lines  146  and the hysteresis synchronisation signal on the hysteresis circuit output line  156  to generate the high side gate drive control signals on the high side gate drive control lines  128  and the low side gate drive control signals on the low side gate drive control lines  130 . 
         [0031]    The described embodiments of the invention are only some illustrative implementations of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims.