Abstract:
An assembly for operating a DC synchronous machine according to an exemplary aspect of the present disclosure includes, among other things, a controller that is configured to determine a position of a rotating portion utilizing a carrier signal, adjust current supply to a field winding, and monitor and adjust operation of the DC synchronous machine based on various electrical parameters relating to the carrier signal. A method for operating a DC synchronous machine is also disclosed.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to a synchronous machine, and more specifically to a control system for synchronizing current supply with rotor position. 
         [0002]    Synchronous machines are known. Synchronous machines include a stationary portion and a rotating portion, where the rotating portion and the stationary portion each have at least one winding. 
         [0003]    One application of synchronous machines is a starter/generator arrangement for gas turbine engines. Synchronous starter/generators are configured to function as a motor to first start a gas turbine engine. Once the engine is running, the synchronous starter/generator can be shifted to operate the machine as a generator. 
         [0004]    An example of a synchronous machine includes a direct current (DC) synchronous machine. When operating as a generator, the DC synchronous machine is configured to supply direct current to one or more loads such as avionics equipment or motor driven loads on an aircraft. When operating as a motor, the DC synchronous machine is coupled to a DC power source in order to supply motive power to a device with moving parts, such as the starter function, or a pump or compressor. 
         [0005]    The DC synchronous machine includes an AC field winding on the rotating portion and a DC armature winding on the stationary portion. Current supplied to the AC field winding generates a magnetic field between the rotating portion and the stationary portion, causing direct current to be generated at the DC armature winding. Commutation of the AC field winding in DC synchronous machines typically requires one or more position sensors, such as resolver or Hall Effect devices, in order to synchronize a frequency of current supply with angular rotation of the rotor. There are complexities associated with integrating position sensors into electrical system. 
       SUMMARY 
       [0006]    An assembly for power generation, according to an exemplary aspect of the present disclosure, includes, among other things, a synchronous machine. The synchronous machine includes a stationary portion and a rotating portion. The stationary portion includes a direct current (DC) armature winding, and the rotating portion includes a rotating inverter coupled to an alternating current (AC) field winding. A carrier generator is configured to cause a carrier signal to be injected into a magnetic field between the AC field winding and the DC armature winding. A controller is configured to cause the rotating inverter to communicate alternating current to the AC field winding at a frequency that is based upon the carrier signal and is adjusted to approach synchronization with a position of the rotating portion. A method of operating a DC synchronous machine is also discussed. 
         [0007]    The various features and advantages of disclosed embodiments will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a DC synchronous machine. 
           [0009]      FIG. 2  schematically illustrates a controller for the DC synchronous machine of  FIG. 1 . 
           [0010]      FIG. 3  schematically illustrates a controller for a DC synchronous machine. 
           [0011]      FIG. 4  schematically illustrates a third embodiment of a controller for a DC synchronous machine. 
           [0012]      FIG. 5  shows a method of adjusting current supply based on rotor position. 
           [0013]      FIG. 6  shows a method of estimating rotor position. 
           [0014]      FIG. 7  shows a second method of estimating rotor position. 
           [0015]      FIG. 8  shows a third method of estimating rotor position. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The disclosed embodiments of a DC synchronous machine include a control assembly configured to cause a carrier signal to be injected into a magnetic field in order to adjust current supply based on an estimated rotor position. The DC synchronous machine can be configured to operate as a motor or a generator, and the control assembly can be configured to supply the carrier signal at various locations in the DC synchronous machine as discussed below. Further embodiments of a DC synchronous machine are disclosed in co-pending U.S. patent application Ser. No. 14/683,468 (Client Reference No. PA35776US; Attorney Docket No. 67036-807PUS1), entitled “DC Synchronous Machine” filed on even date herewith. Aspects of this function from the co-pending application are incorporated herein by reference. 
         [0017]      FIG. 1  illustrates a DC synchronous machine  100  that may be configured to supply direct current to one or more loads  102  if operating as a generator. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. 
         [0018]    The DC synchronous machine  100  includes a stationary portion  104 , or stator, arranged about a rotating portion  106 , or rotor, to define an air gap  108 . The rotating portion  106  can be coupled to a prime mover  110  via a shaft  112 . Example prime movers  110  can include gas turbine engines for aircrafts and ground-based systems, and diesel engines. The rotating portion  106  and the stationary portion  104  include wire coils. During operation in a generator mode, a rotating magnetic field is generated by supplying current to the wire coils at the rotating portion  106  while the rotating portion  106  rotates relative to the stationary portion  104 . 
         [0019]    A controller  114  is coupled to the DC synchronous machine  100  to cause various characteristics of the rotating magnetic field to be adjusted, as discussed in detail below. The DC synchronous machine  100  can be coupled to a DC power source  152  in order to generate mechanical output in a motor mode to drive the prime mover  110 . The DC synchronous machine  100  can also be configured to function in a generator mode to supply direct current to one or more loads  102 . As an example, the DC synchronous machine  100  can be a starter/generator which operates to start rotation of a gas turbine engine, and then is driven by the gas turbine engine to generate current. 
         [0020]    Referring to  FIG. 2 , the stationary portion  104  includes a stator armature winding  116 , and the rotating portion  106  includes a three-phase alternating current (AC) field winding  118 . Although a three-phase AC field winding is shown, any number of phases can be utilized with the teachings herein. A rotor energy source  120  is configured to energize the AC field winding  118  in order to induce a magnetic field between the AC field winding  118  and a stator armature winding  116 . In the illustrative embodiment, the rotor energy source  120  is a rechargeable energy source, such as a supercapacitor (shown) or lithium ion battery, located at the rotating portion  106 . The rechargeable rotor energy source  120  is configured to operate in charge and supply modes. During supply mode, power is supplied from the rotor energy source  120  to the AC field winding  118 . During charge mode, power is supplied to the rotor energy source  120  from the AC field winding  118  by injecting high frequency power into the stator armature winding  116 . Further embodiments for the configuration and operation of a rechargeable rotor energy source are disclosed in co-pending U.S. patent application Ser. No. 14/683,468 (Client Reference No. PA35776; Attorney Docket No. 67036-807PUS1). Aspects of this function from the co-pending application are incorporated herein by reference. In alternative embodiments, the rotor energy source  120  is a synchronous exciter, a permanent magnet exciter, or a high frequency transformer, for example. 
         [0021]    A supply of direct current from the rotor energy source  120  is communicated to a rotating inverter  122  configured to convert direct current to alternating current. The rotating inverter  122  can include transistor(s)  124  and diode(s)  126  configured to selectively provide a supply of alternating current to the AC field winding  118 . 
         [0022]    Communication of alternating current from the rotating inverter  122  to the AC field winding causes the rotating magnetic field to be generated between the AC field winding  118  and the stator armature winding  116 . The rotating magnetic field induces a current in the stator armature winding  116  to generate DC output at terminal  103   a,    103   b.    
         [0023]    The rotating portion  106  can include a current regulator  128  configured to selectively adjust a frequency of current communicated from the rotating inverter  122  to the AC field winding  118 . The current regulator  128  can be coupled to one or more current sensors  140  to determine a current output at each phase of the rotating inverter  122 . The current regulator  128  can selectively adjust the current supply from the rotating inverter  122  to the AC field winding  118  based on the current output at each phase of the rotating inverter  122  and rotor position information determined by the controller  114 . The controller  114  is configured to alter current supplied to the rotating inverter  122  such that a frequency of the supply current is synchronized with a position of the rotating portion  106 , shaft  112 , or the rotating magnetic field relative to the stationary portion  104 . 
         [0024]    A feedback arrangement is utilized to determine the position of the rotating portion  106 . A carrier generator  130  is configured to generate a carrier signal at a predetermined frequency. The carrier generator  130  injects the carrier signal at a location of the DC synchronous machine  100 , such as the current regulator  128 , for example. The current regulator  128  is configured to communicate the carrier signal to the rotating inverter  122 , such that the carrier signal is injected into the rotating magnetic field. The DC synchronous machine  100  can include an output filter  150 , such as one or more low-pass filters  151   a,    151   b,  configured to filter the high frequency carrier signals such that the signals do not interrupt the DC load  102 . 
         [0025]    The controller  114  also includes a rotor position/speed estimator  132  configured to determine rotor position. Rotor position/speed estimator  132  is coupled to voltage sensor  131  to obtain a voltage signal at the stator armature winding  116 . The obtained voltage signal contains angular information about the rotating portion  106  at a frequency of the carrier signal. An encoder/decoder  134  communicates the carrier signal to the rotor position/speed estimator  132  via signal line  135 . The rotor position/speed estimator  132  is configured to isolate the measured voltage signal at the carrier frequency to determine the position of the rotating portion  106 . Various techniques for estimating the position of the rotating portion  106  are described below with reference to  FIGS. 6-8 . 
         [0026]    The position information is communicated from the rotor position/speed estimator  132  to an encoder/decoder  134  via signal line  133 . The encoder/decoder  134  translates the information in a format to allow a communication transformer  136  to supply the information across the air gap  108  to an encoder/decoder  138  located at the rotating portion  106 . The encoder/decoder  138  communicates the rotor position information to the current regulator  128 . The current regulator  128  is configured to utilize the rotor position information to selectively adjust a frequency of current communicated from the rotating inverter  122  as previously discussed. The controller  114  is configured to determine a position of the rotating portion  106  without the use of position sensors, thereby reducing system complexity. 
         [0027]    The controller  114  can include a voltage regulator  146  configured to receive signals from current sensor(s)  142  via signal line  141 , and signals from voltage sensor(s)  144  via signal line  143 . The voltage regulator  146  can also be configured to receive signals from the rotor position/speed estimator  132  via signal line  137 . The voltage regulator  146  can be configured to monitor DC power supplied from a DC power source  152  (shown in  FIG. 1 ) to the DC synchronous machine  100 , as well as other operating conditions from a health monitor sequencing module  148 , for example, such as current magnitude. The monitored information can be communicated from the voltage regulator  146  to the encoder/decoder  134  via signal line  149 , transferred from the communication transformer  136  to encoder/decoder  138  and then to the current regulator  128 . The current regulator  128  can utilize this information in order to adjust current supply to achieve desired output voltage generated at the stator armature winding  116 . 
         [0028]    The controller  114  can also include a health monitor sequencing module  148  configured to receive one or more signals from the voltage regulator  146  at signal line  147  to monitor output voltage and power supply, and the encoder/decoder at signal line  145  to monitor field current at the AC field winding  118 , for example. The health monitor sequencing module  148  can be configured to monitor operation and status of the DC synchronous machine  100 , such as operating temperature. The health monitor sequencing module  148  can also be configured to inform other systems of various conditions of the DC synchronous machine  100 , such as fault conditions or low-power conditions and the like. 
         [0029]    In operation, the controller  114  utilizes the carrier signal to determine a position of the rotating portion  106  in order to inform the current regulator  128 . The current regulator  128  selectively controls current supplied from the rotating inverter  122  to the AC field winding  118  such that the frequency of the current is synchronized with the position of the rotating portion  106 . Synchronization refers to adjusting current supplied to each phase of a field winding to cause the wave cycles per second (frequency, Hz) of the current at each phase to be equivalent to the revolutions per second (angular frequency, ω) of a rotor. Current through the AC field winding  118  generates a magnetic field, which induces current in the stator armature winding  116  to generate DC output. The current regulator  128  also selectively controls current supplied from the rotating inverter  122  to the AC field winding  118  based on system conditions, such as a desired or sensed output voltage at the stator armature winding  116 . 
         [0030]      FIG. 3  illustrates a second embodiment of a DC synchronous machine  200  configured to operate in a motor mode to generate mechanical output, such as for providing torque to a pump or compressor. In this embodiment, the DC synchronous machine  200  is configured to obtain power from a DC power source  252  coupled to an H-bridge circuit  254 , for example. The H-bridge circuit  254  can include transistor(s)  256  and diode(s)  258 , for example, and is configured to selectively adjust current supplied from the DC power source  252  to a stator armature winding  216 . A current regulator  260  is configured to control current in the DC winding  216  in response to a current command on line  261  from a torque/speed module  246 . 
         [0031]    A controller  214  can include the torque/speed module  246  configured to receive signals from current sensor(s)  242  via signal line  241  and voltage sensor(s)  244  via signal line  243 . The torque/speed module  246  can be configured to control torque and speed of a shaft  112  (shown in  FIG. 1 ) caused by mechanical output generated by DC synchronous machine  200 , as well as to communicate the current command to the rotating current regulator  228 . The current command can be communicated to a current regulator  260  via signal line  261  in order to achieve field weakening operation above a motor base speed of the DC synchronous machine  200 . 
         [0032]    The controller  214  can also include a health monitor sequencing module  248  configured to receive signals from the torque/speed module  262  from signal line  247 . The health monitor sequencing module  248  can be configured to monitor operation and status of the DC synchronous machine  200 . The health monitor sequencing module  248  can also be configured to inform other systems of system conditions such as fault conditions, provide built-in-test and start/stop commands, for example. 
         [0033]    In operation, the DC power source  252  supplies current to the stator armature winding  216  in order to generate a first magnetic field. The first magnetic field can be controlled by the current regulator  260  based on various system conditions, such as a desired output mechanical energy. The current regulator  260  selectively controls the H-bridge  254  to adjust current supplied from the DC power source  252  to the stator armature winding  216 . Simultaneously, a rotor energy source  220  communicates current to the rotating inverter  222 . The controller  214  utilizes a carrier signal to determine the position of the rotating portion  206  in order to inform the current regulator  228  as described above. The current regulator  228  is configured to selectively control current supplied from the rotating inverter  222  to the AC field winding  218  such that the frequency of current supply is synchronized with a position of the rotating portion  206 . Current supply to the AC field winding  218  generates a second magnetic field. Interactions between the first and second magnetic field cause the rotating portion  206  to rotate and provide mechanical energy to drive a shaft  112  (shown in  FIG. 1 ), for example. 
         [0034]      FIG. 4  illustrates a third embodiment of a DC synchronous machine  300  configured to operate in generator and motor modes. One or more switches  376  selectively couple a load  302  to the DC synchronous machine  300 . One or more switches  376  also selectively couple a DC power source  352  and an auxiliary DC power source  362  to the DC synchronous machine  300 . The position of switches  376  determine whether the DC synchronous machine  300  operates in a generator mode or a motor mode. As shown, the switches  376  are arranged such that the DC synchronous machine  300  operates in a generator mode. The relatively lower power auxiliary DC power source  362  can be configured to supply power to the H-bridge  354  when the DC synchronous machine  300  is operating in a generator mode and does not require the high power capability of DC power source  352 . A health monitor sequencing module  348  is coupled to the switches  378  via signal line  375 , and is configured to selectively actuate the switches  378  such that the DC synchronous machine  300  operates in the desired mode. 
         [0035]    A carrier generator  330  injects a carrier signal into the DC synchronous machine  300  at a current regulator  360 , for example, which communicates the carrier signal through an H-bridge circuit  354  and to a stator armature winding  316 . High frequency current induced in the stator armature winding  316  induces a current through the AC field winding  318  on the rotating portion  306 . Voltage sensors  331   a,    331   b,    331   c  are located at the AC field winding  318  are configured to measure voltage for each of the phases. The three phase voltage signals are communicated to a rotor position/speed estimator  332 . 
         [0036]    In the illustrative embodiment, the rotor position/speed estimator  332  is located at a rotating portion  306 . In alternative embodiments the rotor position/speed estimator  332  can be located on the stationary portion  304  or another location. The rotor position/speed estimator  332  is configured to determine a position of the rotating portion  306  and inform a current regulator  328 . The current regulator  328  is configured to adjust current supplied from a rotating inverter  322  by a rotor energy source  320  based on the estimated position of the rotating portion  306  and a desired current magnitude commanded by a voltage regulator/torque-speed module  347  via encoder/decoder modules  334  and  338 . 
         [0037]    In operation, current through the AC field winding  318  generates a first magnetic field. The controller  314  utilizes a carrier signal injected into the magnetic field to determine the position of the rotating portion  306  in order to inform the current regulator  328 . The current regulator  328  selectively controls current supplied from the rotating inverter  322  to the AC field winding  318  such that the frequency of current supply is synchronized with position of the rotating portion  306 . 
         [0038]    In operation as a generator, the first magnetic field induces a current in the stator armature winding  316  to generate DC output to a load  302 . The current regulator  328  also selectively controls current supplied from the rotating inverter  322  to the AC field winding  318  based on various system conditions, such as desired output voltage. 
         [0039]    In operation as a motor, the DC power source  352  supplies current to a stator armature winding  316  in order to generate a second magnetic field. The second magnetic field can be controlled by the current regulator  360  based on system conditions, such as output mechanical energy measured by the torque applied to a shaft  112  (shown in  FIG. 1 ). Interactions between the first and second magnetic fields cause the rotating portion  306  to rotate and provide mechanical energy to drive the shaft  112  (shown in  FIG. 1 ), for example. 
         [0040]    In alternative embodiments, the DC synchronous machine is configured to operate in either generator mode or motor mode as shown in  FIG. 4 , but is configured to have a carrier generator  330 ′ inject the carrier signal into the rotating portion  304  similar to  FIGS. 2 and 3 . 
         [0041]      FIG. 5  illustrates a method  441  in a flowchart for adjusting various characteristics of a rotating magnetic field of a DC synchronous machine, such as DC synchronous machines  100 ,  200 , and  300 . At step  464 , a carrier signal is injected into a first location of a DC synchronous machine, such as an AC field winding or a stator armature winding. The carrier signal has a known frequency and can be generated by a carrier generator. At step  466 , current flow through a winding at a first location causes the carrier signal to be injected into a rotating magnetic field, where the magnetic field induces a current in a second winding. 
         [0042]    At step  468 , an electrical parameter at the carrier signal frequency is detected at a second location, such as the second winding. This electrical parameter can be voltage, for example. At step  470 , rotor position is estimated by evaluating the electrical parameter at the predetermined carrier frequency. At step  472 , the rotor position information is communicated to a current regulator. At step  474 , the current regulator selectively adjusts the current supply from a rotating inverter such that a frequency of current supply is synchronized with the rotor position. 
         [0043]      FIGS. 6-8  illustrate various techniques for estimating rotor position at step  470  of  FIG. 5 , utilizing the rotor position estimator  132 ,  232 ,  332 , for example.  FIG. 6  illustrates a method  577  for estimating position of the rotating portion when a carrier signal having a known frequency is injected into a stator armature winding. At step  578 , three-phase voltages Va, Vb, Vc are measured at a main field winding. The three-phase voltages Va, Vb, Vc contain rotor position information at the carrier frequency. At step  580 , the triangular carrier signal is modulated to output a sinusoidal modulating signal. The sinusoidal modulating signal is combined with Va at step  582 , and the combined signal is passed through a low pass filter at step  584  and combined with the sinusoidal modulating signal. This process is repeated for Vb and Vc. The sinusoidal signals at the output of step  584  are then transformed from 3-phase to 2-phase at step  586 . The sine and cosine components of the 2-phase signal are processed by a phase locked loop that include steps  588 ,  590  and  592 . At step  590 , the speed signal is selected using a proportional integral (PI) controller to estimate a speed of the rotating portion. At step  592 , the output from step  590  is integrated to estimate rotor position. 
         [0044]      FIG. 7  illustrates a method  693  of estimating rotor position when a carrier signal having a predetermined frequency is injected into an AC field winding. At step  678 , a voltage signal (Vsense) is obtained at a DC armature winding containing rotor position information at the carrier frequency. At step  680 , the carrier signal is modulated to output sine and cosine modulating signals. At step  682 , these signals are combined with the voltage signal received at step  678 , and then passed through a low pass filter at step  684 . At step  685 , rotor position is determined based on an output of an arctangent function using the signal components, or Fourier coefficients, determined at step  684 . 
         [0045]      FIG. 8  illustrates an alternative method  795  of estimating rotor position when a carrier signal having known frequency is injected into an AC field winding. Steps  778 ,  780 ,  782 ,  784  are the same as the steps in  FIG. 7  to output the same signal components, or Fourier coefficients, at the output of a low pass filter. At step  787 , the components are combined with the modulated carrier signal. At step  789 , the sum of the components at the output of step  787  are used to reconstruct a filtered signal. At step  791 , zero-cross detectors are used to determine the zero-crossing point for both the reconstructed filtered signal and the sinusoidal modulated carrier signal. The zero-crossing point for both the reconstructed filtered signal and the sinusoidal modulated carrier signal are utilized at step  793  to determine the phase difference between both signals using a counter and a latch register. The phase difference between the signals indicates the rotor position. 
         [0046]    The controller arrangements discussed herein achieve synchronization of the rotor position and the frequency of current supplied to a DC synchronous machine, without the need for speed and position sensors. Synchronization occurs using voltage information already used in controlling the DC synchronous machine, such as the sensors used to monitor system conditions for the health monitor sequencing module  148  in  FIG. 2 . This reduces costs and complexity associated with traditional position sensors. While exact synchronization is preferable, this disclosure extends to attempting to approach synchronization in the disclosed manner. 
         [0047]    Although the different examples have a specific component shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. It should also be understood that any particular quantities disclosed in the examples herein are provided for illustrative purposes only. 
         [0048]    Furthermore, the foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.