Abstract:
Embodiments of the invention provide methods of controlling a motor, such as a servo motor. One method can include monitoring a current temperature of the motor and a power stage of the motor substantially continuously and substantially in real-time. This method can include determining optimum settings for a first time interval to remove power and the second time interval to provide power in order to deliver maximum output while remaining below the maximum rated temperature of the motor. One method can include pulsing power to the motor for a second time interval after a first time interval has elapsed and tailoring pulse shapes of the power provided to the motor for the second time interval. One method can include calculating a maximum phase current based on the rotor shaft torque for each real-time speed of the motor that correlates to the maximum allowable current draw from the power supply.

Description:
BACKGROUND 
       [0001]    Electric motors driving a load typically draw a current in relation to the load. The electric motors must be rated for the highest expected peak current. Thus, the maximum peak current dictates the dimensioning of the cables and wires. Additional electronic equipment of the electric motors must also be rated for the maximum peak current. 
         [0002]    Electric motors generate heat which can be correlated to current draw. Typically, electric motors include heat sinks in order to help prevent overheating. When electric motors stalls due to an unexpected high load, a detrimental peak current may be drawn which can damage electronic equipment and/or the electric motor itself. 
       SUMMARY 
       [0003]    Some embodiments of the invention provide a method of controlling a motor. The method can include monitoring a current temperature of the motor and a power stage of the motor substantially continuously and substantially in real-time. The method can include determining whether the current temperature of the motor approaches a maximum rated temperature of the motor and removing power from the motor for a first time interval. The method can include supplying power to the motor for a second time interval after the first time interval has elapsed. The method can include determining that the current temperature of the motor is decreasing and decreasing the first time interval and/or increasing the second time interval until the current temperature starts increasing. The method can also include determining that the current temperature of the motor is increasing and increasing the first time interval and/or decreasing the second time interval until the current temperature starts decreasing. In addition, the method can include determining optimum settings for the first time interval and the second time interval in order to deliver maximum output while remaining below the maximum rated temperature of the motor. 
         [0004]    Embodiments of the invention provide a method including monitoring a current temperature of the motor and a power stage of the motor substantially continuously and substantially in real-time. The method can include determining whether the current temperature approaches a maximum rated temperature of the motor and removing power from the motor for a first time interval. The method can include pulsing power to the motor for a second time interval after the first time interval has elapsed and tailoring pulse shapes of the power provided to the motor for the second time interval. 
         [0005]    Some embodiments of the invention, provide a method including determining a maximum allowable current draw allowed from the power supply. The method can include monitoring a real-time speed of the motor substantially continuously and monitoring a rotor shaft torque of the motor substantially continuously. The method can include calculating a maximum phase current based on the rotor shaft torque for each real-time speed of the motor that correlates to the maximum allowable current draw from the power supply. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1A  is a perspective view of a servo motor according to one embodiment of the invention. 
           [0007]      FIG. 1B  is a cross-sectional view of the servo motor of  FIG. 1A . 
           [0008]      FIG. 2  is a schematic diagram of a controller for use with the servo motor according to one embodiment of the invention. 
           [0009]      FIG. 3  is a schematic block diagram illustrating connections between the servo motor, additional electrical components, and electronic equipment according to some embodiments of the invention. 
           [0010]      FIG. 4  is a schematic block diagram of a load dump protection system according to one embodiment of the invention. 
           [0011]      FIG. 5  is flowchart of a load dump protection method according to one embodiment of the invention. 
           [0012]      FIG. 6  is a flowchart of a power management control of the servo motor according to one embodiment of the invention. 
           [0013]      FIGS. 7A through 7D  are schematic graphs of various pulse shapes according to some embodiments of the invention. 
           [0014]      FIG. 8  is a flowchart of a current fold back protection method according to one embodiment of the invention. 
           [0015]      FIG. 9  is a schematic block diagram of a rectification bridge according to one embodiment of the invention. 
           [0016]      FIG. 10  is a flow chart of an operation of the rectification bridge of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0018]    The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
         [0019]      FIG. 1A  illustrates a perspective view of a servo motor  10  according to one embodiment of the invention. The servo motor  10  can include a housing  12 , a heat sink  14 , a stand  16 , and connectors  18 . The heat sink  14  can include ribs  20 , which can be positioned around a perimeter of the housing  12 . The stand  16  can be used to securely mount the servo motor  10  in a suitable location. The connectors  18  can be used to supply power to the servo motor  10 . In some embodiments, a controller  22  can be housed within the servo motor  10 . In other embodiments, the controller  22  can be coupled to the housing  12  of the servo motor  10 . The controller  22  can include a connector  24 , which can enable the controller  22  to connect to additional electronic equipment. In some embodiments, the connector  24  can be used to supply power to the controller  22 . 
         [0020]      FIG. 1B  illustrates a cross-sectional view of the servo motor  10  according to one embodiment of the invention. The servo motor  10  can include a rotor shaft  26 , one or more rotors  28 , and a stator  30 . The rotor shaft  26  can be coupled to the housing  12  with one or more bearings  32  enabling the rotor shaft  26  to rotate with respect to the housing  12 . The rotor shaft  26  can include a first end  34  and a second end  36 . The first end  34  can include a coupling  38 , which can enable the servo motor  10  to connect to peripherals, such as, for example, pumps. The second end  36  can extend beyond the housing  12 . In some embodiments, the second end  36  can extend into the controller  22 . The second end  36  can include projections  40 . A sensor  42  can be positioned adjacent to the second end  36 . The sensor  42  can include an encoder and/or a resolver. The sensor  42  can measure a rotor shaft speed and/or a rotor shaft angle, such as disclosed in U.S. Pat. Nos. 6,084,376 and 6,525,502 issued to Piedl et al., the entire contents of which are herein incorporated by reference. 
         [0021]    In some embodiments, the rotor  28  can be a permanent-magnet rotor. The rotor  28  can be positioned inside the stator  30 . The stator  30  can include a stator core  44  and stator windings  46 . In some embodiments, the rotor  28  can rotate to drive the rotor shaft  26 , while the stator core  44  and the stator windings  46  can remain stationary. The connectors  18  can extend into the housing  12  toward the rotor shaft  26 . The connectors  18  can be coupled to the stator  30 . 
         [0022]    In some embodiments, the sensor  42  can be built into the motor housing  12  to accurately indicate the position and/or speed of the rotor shaft  26 . In other embodiments, the sensor  42  can be included in the controller  22 . In some embodiments, the speed of the rotor shaft  26  of the servo motor  10  can be substantially continually monitored via a feedback device, such as an encoder, resolver, hall effect sensors, etc. In other embodiments, the speed of the rotor shaft  26  of the servo motor  10  can be measured without a physical sensor (e.g., by extracting information from a position of the rotor shaft  26 ). 
         [0023]    The term “servo motor” generally refers to a motor having one or more of the following characteristics: a motor capable of operating at a large range of speeds without over-heating, a motor capable of operating at substantially zero speed and retaining enough torque to hold a load in position, and/or a motor capable of operating at very low speeds for long periods of time without over-heating. The term “torque” can be defined as the measured ability of the rotor shaft to overcome turning resistance. Servo motors can also be referred to as permanent-magnet synchronous motors, permanent-field synchronous motors, or brushless electronic commutated motors. 
         [0024]    The servo motor  10  can be capable of precise torque control. The output torque of the servo motor  10  can be highly responsive and substantially independent of a position of the rotor  28  and a speed of the rotor shaft  26  across substantially the entire operating speed range. In some embodiments, a current draw of the servo motor  10  can be sent to the controller  22  and can be used to compute the torque necessary to drive the servo motor  10 . 
         [0025]    A conventional DC electric motor can rely on pulse width modulation (PWM) control for operating a peripheral at low rotations per minute (RPM). Especially when the peripheral includes moving a high load, PWM control of a conventional DC electric motor can compromise accurate speed control in order to prevent a stall condition. The use of the servo motor  10  can simplify the actuation and operation of the peripheral. As a result, the servo motor  10  can enable a smooth operation of the peripheral. In some embodiments, the use of the servo motor  10  can allow a smooth operation of the peripheral even at low RPM, which can result in an optimized speed control. In some embodiments, the servo motor  10  can help decrease mechanical wear of the peripheral. 
         [0026]    The controller  22  can be external to the servo motor  10  or housed inside the servo motor  10 . As shown in  FIG. 2 , the controller  22  can include a digital signal processor (DSP)  48 , and memory  50 . The memory  50  can include random access memory (RAM), read only memory (ROM), and/or electrically erasable programmable read only memory (EEPROM). In some embodiments, the controller  22  can include an analog/digital (A/D) converter and/or a digital/analog (D/A) converter in order to process different input signals and/or to interface with other devices and/or peripherals. In some embodiments, the DSP  48  and/or the memory  50  can be positioned inside or near the servo motor  10  while in other embodiments, the DSP  48  and/or the memory  50  can be housed separately and positioned some distance away from the servo motor  10 . In some embodiments, space restrictions and/or thermal loads generated by the servo motor  10  can dictate a position of the controller  22 . 
         [0027]      FIG. 3  is a schematic block diagram illustrating connections between the servo motor  10 , electrical components, and/or electronic equipment according to one embodiment of the invention. On a line  52 , the controller  22  can receive an external command to operate the servo motor  10 . In some embodiments, the external command can be indicative of a base speed at which the servo motor  10  should be operated. If the servo motor  10  is not running, the external command can be transmitted directly to the servo motor  10  over a line  54 . Once the servo motor  10  is running, the DSP  48  can process one or more of the following signals from the servo motor  10 : the speed of the rotor shaft  26  (line  56 ), the angle of the rotor shaft  26  (line  58 ), the current draw of the servo motor  10  (line  60 ), and a temperature of the servo motor  10  (line  62 ). Any suitable combination of these signals or additional signals can be used by the DSP  48  to modify and/or override the external command to provide closed-loop control. 
         [0028]    In some embodiments, the actual speed of the rotor shaft  26  of the servo motor  10  can be transmitted back to the DSP  48  via the line  54 . In some embodiments, the DSP  48  can use a difference between the base speed and the actual speed of the rotor shaft  26  to modify the operation of the servo motor  10 . In some embodiments, the controller  22  can use one or more of the speed of the rotor shaft  26 , the torque of the rotor shaft  26 , and the position of the rotor shaft  26  to operate the servo motor  10 . 
         [0029]    In some embodiments, the controller  22  can provide drive diagnostics for the servo motor  10 , which can be downloaded for further processing. A technician can use the drive diagnostics to analyze any errors of the servo motor  10  and/or the controller  22 . The drive diagnostics can include error messages specifically for the servo motor  10 . In some embodiments, the servo motor  10  can communicate the following types of errors to the controller  22 : one or more components of the servo motor  10  exceed threshold temperatures, the servo motor  10  requires a higher current for the operation than a threshold current (which can be referred to as “current fold back”), and the servo motor  10  is experiencing a stall condition. If an error is communicated from the servo motor  10  to the DSP  48  via a line  64 , the controller  22  can stop the servo motor  10 . In some embodiments, the controller  22  can be capable of detecting an interrupted connection between electrical components and/or electronic equipment and can generate an error. 
         [0030]    In some embodiments, the rapid compute time of the controller  22  can allow for several evaluations and/or modifications of the external command per rotation of the rotor shaft  26 . This can result in rapid adjustments to varying parameters and/or conditions of the servo motor  10  and/or the peripheral, while helping to provide a substantially uninterrupted and smooth operation of the servo motor  10 . 
         [0031]    As shown in  FIG. 3 , the servo motor  10  can be powered by an external power source  66 . The external command can be sent from the DSP  48  via the line  54  to a power device  68 , which can be connected to the external power source  66 . Depending on the external command received from the DSP  48 , the power device  68  can provide the appropriate power (e.g., the appropriate current draw) to the servo motor  10 . In some embodiments, the power device  68  can supply the servo motor  10 , the controller  22 , and additional electrical components and/or electronic equipment with power. In some embodiments, the power device  68  can be integrated with the controller  22 . 
         [0032]    In some embodiments, a load dump protection circuit  70  can be used to operate the servo motor  10 . In some embodiments, the load dump protection circuit  70  can be part of the power device  68 . The load dump protection circuit  70  can prevent an over-voltage peak from causing damage to the servo motor  10 , the controller  22 , and other electrical components and/or electronic equipment. In some embodiments, the load dump protection circuit  70  can protect at least part of the electrical components and/or electronic equipment from an under-voltage condition and/or a wrong polarity of the external power source  66 . In some embodiments, the load dump protection circuit  70  can disconnect the electrical components and/or electronic equipment, if the voltage of the external power source  66  is negative, below a minimum, or above a specified level. 
         [0033]      FIG. 4  illustrates the load dump protection circuit  70  according to one embodiment of the invention. The load dump protection  70  can include a sensing circuit  72 , a relay contact  74 , a relay coil  76 , a capacitor  78 , a first diode  80 , a second diode  82 , and a current source  84 . The relay coil  76  can be connected to the sensing circuit  72 . The relay coil  76  can energize and de-energize the relay contact  74 . Before the relay contact  74  closes, the current source  84  can charge the capacitor  78  with a limited current to enable a “soft start.” Once the capacitor  78  is charged to the correct level, the current source  84  and the second diode  82  can be bypassed by the relay contact  74  enabling the high currents of normal operation to flow. 
         [0034]    The first diode  80  and the second diode  82  can prevent damage to the sensing circuit  72  and/or other electronic equipment, if the voltage supplied from the external power supply  66  has the wrong polarity. For example, if the external power supply  66  is a battery, which is being disconnected for maintenance and/or repair procedures, the first diode  80  and the second diode  82  can prevent damage to the electronic equipment, if the battery is re-connected incorrectly. 
         [0035]    In some embodiments, the sensing circuit  72  can withstand an over-voltage peak. The sensing circuit  72  can also rapidly detect the over-voltage peak or an under-voltage condition. The sensing circuit  72  can detect the over-voltage peak or the under-voltage condition substantially independent of a power status of the servo motor  10  and/or the controller  22 . In some embodiments, the sensing circuit  72  can detect the over-voltage peak or the under-voltage condition even if the servo motor  10  and/or the controller  22  are not running. The sensing circuit  72  can de-energize the relay contact  74  through the relay coil  76 . As a result, all of the internal power supplies can be switched off almost immediately. In some embodiments, the current source  84  can charge the capacitor  78  with the limited current before the relay contact  74  is re-energized again. The sensing circuit  72  can re-energize the relay contact  74  and can re-connect all internal power supplies once no over-voltage conditions, such as over-voltage peaks, or under-voltage conditions are being detected. In some embodiments, the relay contact  74  can be re-energized once no over-voltage conditions or under-voltage conditions are being detected and the capacitor  78  is charged to the correct level. Once the relay contact  74  is re-energized, the second diode  82  and the current source  84  can be bypassed by the relay contact  74  to enable the supply of normal operating currents. For example, if welding is being performed in the vicinity of the servo motor  10  for repairs, maintenance, or equipment installation, over-voltage peaks can travel toward the servo motor  10 . The load dump protection circuit  70  can help prevent possible damage to the servo motor  10  and the electronic equipment caused by the over-voltage peaks. 
         [0036]      FIG. 5  is a flow chart describing a load dump protection method  200  according to one embodiment of the invention. In some embodiments, the sensing circuit  72  can sense (at step  202 ) a voltage U supply . If the voltage U supply  is less than a maximum threshold U max  but higher than a minimum threshold U min  (at step  204 ), the sensing circuit  72  can sense (at step  202 ) the voltage U supply  again. If the voltage U supply  is higher than the maximum threshold U max  or below the minimum threshold U min  (at step  204 ), the sensing circuit  72  can disconnect (at step  206 ) the electronic equipment including the servo motor  10 , the controller  22 , and/or other electronics substantially before the over-voltage condition or the under-voltage condition can cause damage to the electronic equipment. In some embodiments, the sensing circuit  72  can disengage the relay  74  to disconnect the electronic equipment. Once disconnected, the sensing circuit  72  can continue to sense (at step  208 ) the voltage U supply  substantially until the voltage U supply  has dropped below the maximum threshold U max  or has risen above the minimum threshold U min  (at step  210 ). The sensing circuit  72  can re-connect (at step  212 ) the electronic equipment, before the load dump protection method  200  is restarted (at step  202 ). In some embodiments, the relay  74  can be re-energized in order to re-connect the electronic equipment. 
         [0037]    The servo motor  10  can generates heat, especially at high RPM. The servo motor  10  can include passive heat controls, such as heat sinks, vent holes, etc. In some embodiments, as shown in  FIG. 6 , the servo motor  10  can use a power management control method  300  to actively prevent over-heating. In some embodiments, the duty cycle of the current supplied to the servo motor  10  can be altered to prevent over-heating. 
         [0038]      FIG. 6  illustrates the power management control method  300  according to one embodiment of the invention. In some embodiments, the DSP  48  can measure (at step  302 ) a temperature (T motor ) of the servo motor  10 . The DSP  48  can measure the temperature of any suitable component of the servo motor  10 . In some embodiments, the DSP  48  can measure the temperature of multiple components. The DSP  48  can determine (at step  304 ), if the temperature T motor  is approaching a maximum temperature T max  (i.e., if the temperature T motor  is within a range ε). The maximum temperature T max  can be stored in the memory  50 , and, if multiple components of the servo motor  10  are monitored by the DSP  48 , the maximum temperature T max  can be component specific. If the maximum temperature T max  does not approach the temperature T motor , the controller  22  can operate (at step  306 ) the servo motor  10  with the external command. The DSP  48  can restart (at step  302 ) the power management control method  300  by measuring the temperature T motor . 
         [0039]    If the temperature T motor  approaches the maximum temperature T max , the DSP  48  can determine (step  308 ) whether the maximum temperature T max  has been exceeded. If the maximum temperature T max  has been exceeded at step  308 , the servo motor  10  can be shut down (at step  310 ) and the DSP  48  can start a timer (at step  312 ). The timer can be set for a time period long enough to allow the servo motor  10  to cool. In some embodiments, the timer can be set for a time period of about one minute. After the timer has been started (at step  312 ), the DSP  48  can continue to monitor (at step  314 ) the temperature T motor  of the servo motor  10 . If the temperature T motor  has dropped below the maximum temperature T max  the DSP  48  can determine whether the timer has expired (at step  316 ). Once the timer has expired (at step  314 ), the DSP  48  can restart (at step  318 ) the servo motor  10  and can measure (at step  302 ) the temperature T motor  again. 
         [0040]    If the temperature T motor  is below the maximum temperature T max  but within the range ε, the DSP  48  can shut down (at step  320 ) the servo motor  10  for a first time interval TI 1 . The DSP  48  can turn on (at step  322 ) the servo motor  10  for a second time interval TI 2 . In some embodiments, the first time interval TI 1  and/or the second time interval TI 2  can be a default value and/or a previously stored value in the controller  22 . In some embodiments, the servo motor  10  can run continuously during the second time interval TI 2 , while in other embodiments, the servo motor  10  can be pulsed with a certain frequency F pulse . The temperature T motor  can be compared (at step  324 ) to a previously stored temperature T prev . In some embodiments, the temperature T prev  can be a default value during initialization; (i.e., if no temperature has been previously stored in the memory  50  since the last power-up of the servo motor  10 ). If the temperature T prev  is lower than the temperature T motor , the DSP  48  can increase (at step  326 ) the first time interval TI i , decrease (at step  328 ) the second time interval TI 2 , and/or decrease (at step  330 ) the frequency F pulse . The DSP  48  can store (at step  332 ) the temperature T motor  as the temperature T prev  in the memory  50 . The DSP  48  can operate (at step  334 ) the servo motor  10  with the first time interval TI 1  and the second time interval TI 2  resulting in a pulsing of the servo motor  10 . In some embodiments, the pulse frequency resulting from the first time interval TI 1  and the second time interval TI 2  can be substantially lower than the frequency F pulse , at which the servo motor  10  can be operated during the second time interval TI 2 . In some embodiments, the frequency F pulse  can be less than about 20 kilohertz. 
         [0041]    If the temperature T motor  is not higher than the temperature T prev  (at step  324 ), the DSP  48  can determine (at step  336 ) whether the temperature T prev  is higher than the temperature T motor . If the temperature T prev  is higher than the temperature T motor , the DSP  48  can decrease (at step  338 ) the first time interval TI 1 , increase (at step  340 ) the second time interval TI 2 , and/or increase (at step  342 ) the frequency F pulse . The DSP  48  can store (at step  332 ) the temperature T motor  as the temperature T prev  in the memory  50 . The DSP  48  can pulse (at step  334 ) the servo motor  10  with the first time interval TI 1  and the second time interval TI 2 . If the temperature T prev  is substantially equal to the temperature T motor , the servo motor  10  can be pulsed (at step  334 ) with the first time interval TI 1  and the second time interval TI 2 . After step  334 , the DSP  48  can restart (at step  302 ) the power management control, method  300 . 
         [0042]    In some embodiments, the power management control method  300  can be self-adapting and can learn the optimal values for at least one of the first time interval TI 1 , the second time interval TI 2 , and the frequency F pulse . As a result, the servo motor  10  can operate at high RPM over prolonged periods of time before having to shut down due to an over-temperature condition. In some embodiments, the power management control method  300  can adjust at least one of the first time interval TI 1 , the second time interval TI 2 , and the frequency F pulse  over a short period of time, while maximizing a work output of the servo motor  10  under the given circumstances without exceeding the maximum temperature T max  and/or shutting down. In some embodiments, the period of time in which the power management control method  300  can learn the optimal values for pulsing the servo motor  10  can be within about 10 rotations of the rotor shaft  26 . 
         [0043]    In some embodiments, the operation of the servo motor  10  with the frequency F pulse  can result in power losses in the servo motor  10  itself, the controller  22 , and/or the power device  68 . The power losses can increase the temperature of the respective component and/or equipment. In some embodiments, the frequency F pulse  can be used to determine a physical location of the power losses. In some embodiments, the frequency F pulse  can be increased to reduce the power losses in the servo motor  10  in order to assist the power management control method  300  in preventing the servo motor  10  from overheating. As a result, the increase frequency F pulse  can increase the power losses in the controller  22  and/or the power device  68 . To prevent overheating of the controller  22  and/or the power device  68 , the frequency F pulse  can be decreased in order to limit the power losses. As a result, the decreased frequency F pulse  can be used to increase the power losses in the servo motor  10 . 
         [0044]    In some embodiments, the power management control method  300  can be used to adjust the frequency F pulse  to balance the power losses. In some embodiments, the power management control method  300  can vary the frequency F pulse  in order to prevent overheating of the servo motor  10  and/or any other electronic equipment. In some embodiments, the power management control method  300  can determine a certain frequency F pulse  depending on an operation point and/or condition of the servo motor  10 . In some embodiments, varying the frequency F pulse  can maximize the overall system efficiency for the operation of the servo motor  10 . 
         [0045]      FIGS. 7A through 7D  illustrate various tailored pulse shapes  400  according to some embodiments of the invention. The tailored pulse shapes  400  can include a step pulse shape  402  ( FIG. 7A ), a linear ramp pulse shape  404  ( FIG. 7B ), a polynomial pulse shape  406  ( FIG. 7C ), and a trigonometric pulse shape  408  ( FIG. 7D ). In some embodiments, a beginning and/or an end of a pulse can be tailored in order to derive the tailored pulse shapes  400 . The polynomial pulse shape  406  can be approximated by any suitable higher polynomial and/or rational function. The trigonometric pulse shape  408  can be approximated by any trigonometric function including sine, cosine, tangent, hyperbolic, arc, and other exponential functions including real and/or imaginary arguments. 
         [0046]    In some embodiments, the power management control method  300  can use the tailored pulse shapes  400 . The tailored pulse shapes  400  can be adjusted to minimize the mechanical wear of the servo motor  10 . In some embodiments, the tailored pulse shapes  400  can minimize mechanical stresses being transferred from the servo motor  10  onto the peripheral. The tailored pulse shapes  400  can be adjusted to optimize the amount of work output for the amount of power supplied to the servo motor  10 . In some embodiments, the tailored pulse shapes  400  can be modified to lower a thermal shock of the servo motor  10 . Heat generated by the servo motor  10  at a high RPM can be reduced so that the servo motor  10  can continue to operate at the high RPM over prolonged periods of time without shutting down due to an over-temperature condition and/or changing the first time interval TI 1 , the second time interval TI 2 , and/or the frequency F pulse . 
         [0047]      FIG. 8  is a flow chart describing a current fold back protection method  500  according to some embodiments. The current fold back protection method  500  can prevent damage to the servo motor  10  from drawing a high current that would damage the servo motor  10 . The current fold back protection method  500  can optimize the operation of the servo motor  10 . In some embodiments, the current fold back protection method  500  can maximize the work output of the servo motor  10 . The current fold back protection method  500  can be performed by the controller  22 . In some embodiments, the DSP  48  can perform the current fold back protection method  500 . The controller  22  can sense (at step  502 ) the speed of the rotor shaft  26 . The controller  22  can sense (at step  504 ) the rotor shaft torque and/or an actual phase current I phase  supplied to the servo motor  10 . In some embodiments, the controller  22  can compute the torque of the rotor shaft  26  with the phase current I phase . The controller  22  can compute (at step  506 ) a maximum motor phase current I motor,max , which can be the highest allowable current being supplied without damaging the servo motor  10  and/or the controller  22 . In some embodiments, the maximum motor phase current I motor,max  can vary with the speed of the rotor shaft  26 . In some embodiments, the controller  22  can multiply the speed of the rotor shaft  26 , the torque of rotor shaft  26 , and an efficiency parameter of the servo motor  10  in order to compute the maximum motor phase current I motor,max . 
         [0048]    If the phase current I phase  is less than the maximum motor phase current I motor,max  (at step  508 ), the controller  22  can compute (at step  510 ) a difference Δ between a continuous current limit I cont  and the phase current I phase . The continuous current limit I cont  can be the maximum current at which the servo motor  10  can substantially continuously run without resulting in an over-temperature of the servo motor  10  and/or the controller  22 . In some embodiments, the continuous current limit I cont  can be based on an overall thermal capacity of the servo motor  10 . The continuous current limit I cont  can be stored in the memory  50 . 
         [0049]    If the continuous current limit I cont  is larger than the phase current I phase , the difference Δ is positive and can be used to optimize (at step  512 ) the operation of the servo motor  10 , for example to increase the efficiency of the peripheral. If the difference Δ is negative, the controller  22  can determine (at step  514 ) whether the continuous current limit I cont  can be exceeded. To determine whether the continuous current limit I cont  can be exceeded, the controller  22  can evaluate a history of supplied currents to operate the servo motor  10  and/or the difference Δ. In some embodiments, the history of supplied currents to operate the servo motor  10  can include computing a root mean square (RMS) value of the supplied current and/or squaring the supplied current and multiplying the time. 
         [0050]    If the continuous current limit I cont  can be exceeded, the controller  22  can operate (at step  516 ) the servo motor  10  with the phase current I phase . If the continuous current limit I cont  may not be exceeded, the controller  22  can operate (at step  518 ) the servo motor  10  with the continuous current limit I cont . If the phase current I phase  is larger than the maximum motor phase current I motor,max  (at step  508 ), the servo motor  10  can be operated with the maximum motor phase current I motor,max  (at step  520 ). At step  522 , the controller  22  can store either one of the phase current I phase , the continuous current limit I cont , and the maximum motor phase current I motor,max , which has been supplied to the servo motor  10 , in the memory  50 . The controller  22  can then restart the current fold back protection method  500  by sensing (at step  502 ) the speed of the rotor shaft  26 . 
         [0051]    If the phase current I phase  is limited to the maximum motor phase current I motor,max  or the continuous current limit I cont , the servo motor  10  can be operated with the maximum motor phase current I motor,max  (at step  520 ) or the continuous current limit I cont  (at step  518 ). Operating the servo motor  10  at the maximum motor phase current I motor,max  or the continuous current limit I cont  can prevent damage to the servo motor  10 . Due to the maximum motor phase current I motor,max  and/or the continuous current limit I cont  being lower than the current draw necessary to operate the servo motor  10 , operating the servo motor  10  at the maximum motor phase current I motor,max  or the continuous current limit I cont  can result in a stall of the servo motor  10 . The controller  22  can detect the stall of the servo motor  10 . In one embodiment, the angle of the rotor shaft  26  of the servo motor  10  can be used to identify a stall condition of the servo motor  10 . Other embodiments of the invention can use the speed of the rotor shaft  26  of the servo motor  10  to detect a stall condition of the servo motor  10 . Once a stall condition has been detected, the servo motor  10  can attempt to operate again after a certain time interval. In some embodiments, the time interval can be about one second so that the servo motor  10  can regain operation again substantially immediately after the stall condition has been removed. 
         [0052]    A power stage rating of the servo motor  10  and/or the controller  22  can be determined by a continuous operating current and a peak operating current. The continuous operating current can influence the heat generated by the servo motor  10  and/or the controller  22 . The peak operating current can determine the power rating of the servo motor  10  and/or the controller  22 . In some embodiments, the servo motor  10  can be designed to achieve a specific torque constant. Multiple parameters can influence the torque constant. In some embodiments, the torque constant can depend on the number of windings  46 , the number of poles of the rotors  28 , the pattern of the windings  46 , the thickness of the wire used for the windings  46 , the material of the wire, the material of the stator  30 , and numerous other parameters. In some embodiments, the temperature of the servo motor  10  can influence the torque constant. As a result, the torque constant can vary because the temperature of the servo motor  10  can change significantly over the course of its operation. In some embodiments, the DSP  48  can include a mapping procedure to compensate for the temperature variation and the resulting change in the torque constant. As a result, the torque of the rotor shaft  26  that is necessary to drive the servo motor  10  can be accurately computed over a large range of temperatures. 
         [0053]    The torque constant can be stored in the memory  50 . In some embodiments, the torque constant can be accessed by the DSP  48 . In some embodiments, the DSP  48  can compute the torque of the rotor shaft  26  that is necessary to drive the servo motor  10  based on the torque constant and the current draw of the servo motor  10 . The torque constant can influence the peak operating current. A large torque constant can result in a low power stage rating of the servo motor  10 . The high torque constant can reduce the peak operating current. In some embodiments, the peak operating current can be reduced from about 110 Amperes to about 90 Amperes. The heat generation during peak operation of the servo motor  10  can be reduced by increasing the torque constant. The large torque constant can lengthen a time period during which the servo motor  10  can operate at peak operating current without overheating. 
         [0054]    In some embodiments, the servo motor  10  can be driven with high torque values down to substantially zero RPM. The high torque values can be achieved by an increased back electromotive force (BEMF) constant of the servo motor  10 . In some embodiments, the BEMF constant can be proportional to the torque constant. The increased BEMF constant can reduce the current necessary to drive the servo motor  10 . As a result, the servo motor  10  can achieve a certain torque of the rotor shaft  26  at the reduced current. The increased BEMF constant can reduce power losses in the controller  22  and/or other electronic equipment. In some embodiments, the BEMF constant can be related to the highest expected load the servo motor  10  is designed to be capable of moving. In some embodiments, the BEMF constant can be at least 3.5 Volts root mean square per thousand RPM (VRMS/KPRM). In some embodiments, the ratio of the BEMF constant to a voltage driving the servo motor  10  can be constant. 
         [0055]    A high BEMF constant can reduce the maximum speed of the rotor shaft  26  at which the servo motor  10  can be driven. In some embodiments, the BEMF constant and the maximum speed of the rotor shaft  26  of the servo motor  10  can be directly proportional. For example, if the BEMF constant is doubled, the maximum speed of the rotor shaft  26  of the servo motor  10  can be halved. The BEMF constant can be a compromise between a low speed requirement, a high speed requirement, and a thermal load requirement of the servo motor  10 . In some embodiments, the low speed requirement of the servo motor  10  can dictate a certain BEMF constant, which can result in the servo motor  10  not being able to fulfill the high-speed requirement in order to fulfill a specific point of operation. 
         [0056]    In some embodiments, the servo motor  10  can use a phase angle advancing technique for the supplied power in order to increase the maximum speed of the rotor shaft  26 . A commutation angle can be advanced by supplying a phase current at an angle increment before the rotor  28  passes a BEMF zero crossing firing angle. The phase angle advancing technique can retard the commutation angle by supplying the phase current at the angle increment after the at least one rotor  28  has passed the BEMF zero crossing firing angle. In some embodiments, the phase angle advancing technique can influence the BEMF constant. In some embodiments, advancing the commutation angle can decrease the BEMF constant. The servo motor  10  can be optimized to a certain point of operation. The angle increment of the phase angle advancing technique can be related to the speed of the rotor shaft  26 . In one embodiment, the angle increment can be about +/−45 electrical degrees. 
         [0057]    In some embodiments, the servo motor  10  can be used to drive a pump. Driving the pump without the phase angle advancing technique can result in a flow rate of 4 gallons per minute (GPM) at a pressure of 150 pounds per square inch (PSI). In one embodiment, the phase angle advancing technique can increase the flow rate to about 5 GPM, which can be delivered at the pressure of 150 PSI. 
         [0058]    In some embodiments, the servo motor  10  can be operated with a direct current (DC) power supply (e.g., a battery of a vehicle). In other embodiments, the servo motor  10  can be operated with an alternating current (AC) power supply (e.g., a generator or alternator of a vehicle or a mains power supply in a building). 
         [0059]    In some embodiments, the servo motor  10  can be powered with different voltages. The voltages can include one or more of 12 Volts, 24 Volts, 48 Volts, 120 Volts, and 240 Volts. The stator windings  46  can be adapted to a specific voltage. The stator windings  46  can be adapted so that the servo motor  10  can operate with more than one power source (e.g., with a DC power supply or an AC power supply). Other embodiments can include different input power stages that allow the servo motor  10  to selectively operate with different voltages and/or power sources. For example, if the servo motor  10  is used for a sprinkler system in a building, the servo motor  10  can be driven by the 120 Volts AC mains power supply. If mains power is lost, the controller  22  can automatically switch to a 12 Volts DC battery power supply to continue the operation of the sprinkler system. 
         [0060]      FIG. 9  illustrates a rectification bridge  600  according to one embodiment of the invention. The rectification bridge  600  can be used to operate the servo motor  10  with an AC power supply. The rectification bridge  600  can include two or more transistors  602 , an AC bus  604 , and a DC bus  606 . The AC bus  604  can connect to the external power supply  66 . The DC bus  606  can be used to supply power to the servo motor  10 . The transistors  602  can each include an intrinsic diode  608 . In some embodiments, the transistors  602  can include metal oxide semiconductor field effect transistors (MOSFETs). In some embodiments, the transistors  602  can be N-type MOSFETs, while in other embodiments, the two transistors  602  can be P-type MOSFETs. In some embodiments, the transistors  602  can include a first transistor  610 , a second transistor  612 , a third transistor  614 , and a fourth transistor  616  configured in an H-bridge. 
         [0061]    In some embodiments, the controller  22  can sense an incoming current I AC  at a first location  618  on the AC bus  604 . In other embodiments, the controller  10  can sense the incoming current I AC  at a second location  620  along with a third location  622  of the rectification bridge  600 . Sensing the incoming current I AC  of the rectification bridge  600  can result in a much higher level of electrical noise immunity instead of, for example, sensing voltages. If the incoming current I AC  is below a threshold current I limit , the intrinsic diodes  608  can be used to rectify the incoming current I AC . If the incoming current I AC  is above the threshold current I limit , the transistors  602  can be used to rectify the incoming current I AC . To rectify the incoming current I AC , the transistors  602  can be turned on by control signals from the controller  22 . The rectification bridge  600  can provide the correct timing for the switching of the transistors  602 . In some embodiments, the control current can prevent a discharge of the DC bus  606  and/or a shortening of the AC bus  604 . 
         [0062]    In some embodiments, a voltage drop across the transistors  602  can be lower than a voltage drop across the intrinsic diodes  608 . As a result, the switching of the transistors  602  can limit the power losses of the rectification bridge  600 , if the incoming current I AC  exceeds the threshold current I limit . In some embodiments, the threshold current I limit  can be low enough to prevent the rectification bridge  600  from overheating due to the power losses of the intrinsic diodes  608 , but high enough to provide substantial immunity to interference and noise on the AC bus  604 . The rectification bridge  600  can have much lower power losses than a conventional rectification bridge including diodes only. As a result, the use of the rectification bridge  600  can enable a higher efficiency and an operation in higher ambient temperatures. In some embodiments, the rectification bridge  600  can limit the power losses to about 30 Watts at an ambient temperature of about 70° C. (160° F.). In some embodiments, the threshold current I limit  can include hysteresis to increase an immunity to the noise on the AC bus  604 . 
         [0063]      FIG. 10  illustrates a rectification method  700  according to one embodiment of the invention. The incoming current I AC  can be sensed (at step  702 ). If the absolute value of the incoming current I AC  is below the current threshold I limit  (at step  704 ), the intrinsic diodes  608  can rectify the incoming current I AC  and the rectification method  700  can be restarted (at step  702 ) with sensing the incoming current I AC . If the absolute value of the incoming current I AC  is above the current threshold I limit  (at step  704 ), the controller  22  can determine (at step  706 ) whether the incoming current I AC  is negative. If the incoming current I AC  is positive, the controller  22  can supply (at step  708 ) the control current to the transistors  602 . In some embodiments, the controller  22  can use the first transistor  610  and the fourth transistor  616 , which can be positioned diagonally across from one another in the rectification bridge  600 . If the incoming current I AC  is negative, the controller  22  can supply (at step  710 ) the control current to the transistors  602 . In some embodiments, the controller  22  can use the second transistor  612  and the third transistor  614 , which can be positioned diagonally across from one another in the rectification bridge  600 . After step  708  and/or step  710 , the rectification method  700  can be restarted by sensing the incoming current I AC  so that the intrinsic diodes  608  can be substantially immediately used for the rectification, if the incoming current I AC  drops below the current threshold I limit . 
         [0064]    It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. 
         [0065]    Various features and advantages of the invention are set forth in the following claims.