Abstract:
A switch-mode power supply that includes a transformer coupled to an alternating current (AC) power source and a direct current (DC) power source, wherein the AC power source is electrically isolated from the DC power source. The switch-mode power supply further includes a first controller configured to regulate a first voltage output from the AC power source, and a second controller configured to regulate a second voltage output from the DC power source when the transformer is not receiving power from the AC output.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter described herein relates generally to electric generators, and more specifically, to methods, systems, and apparatus that enable a switch-mode power supply to have a dual primary transformer that derives a low voltage power supply from two different power sources of disparate voltage ratings. 
         [0002]    A switched-mode power supply (SMPS) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load while converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from an input voltage. 
         [0003]    Electronic voltage regulators are used to regulate the output voltage of a brushless synchronous generator by controlling the level of current in an exciter field of the generator. The power source for the excitation is most often derived from a relatively small permanent magnet generator (PMG) that is part of a larger, main generator. However, because a rotor of the PMG is mounted to the same shaft as a rotor of the main generator, it is required that a prime mover of the main generator be rotating in order for the electronic voltage regulator to receive input power. As such, if the prime mover of the main generator is not rotating, the electronic voltage regulator module is unable to perform system monitoring (e.g., temperature monitoring) or perform communication with other system elements because power is not being supplied to the electronic voltage regulator. Thus, the electronic voltage regulator module cannot perform system monitoring nor communication functions until the prime mover begins rotating and power is once again provided to the electronic voltage regulator. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one aspect, a switch-mode power supply is provided. The switch-mode power supply includes a transformer coupled to an alternating current (AC) power source and a direct current (DC) power source, wherein the AC power source is electrically isolated from the DC power source. The switch-mode power supply further includes a first controller configured to regulate a first voltage output from the AC power source, and a second controller configured to regulate a second voltage output from the DC power source when the transformer is not receiving power from the AC output. 
         [0005]    In another aspect, a system that includes an alternating current (AC) power source, a direct current (DC) power source, and a transformer is provided. The transformer is coupled to the AC power source and the DC power source, wherein the AC power source is electrically isolated from the DC power source. The transformer includes a first controller configured to regulate a first voltage output from the AC power source, and a second controller configured to regulate a second voltage output from the DC power source when the transformer is not receiving power from the AC output. 
         [0006]    In yet another aspect, a transformer is provided. The transformer is coupled to an alternating current (AC) power source and a direct current (DC) power source, wherein the AC power source being electrically isolated from the DC power source. The transformer includes a first controller configured to regulate a first voltage output from the AC power source, and a second controller configured to regulate a second voltage output from the DC power source when the transformer is not receiving power from the AC output. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic diagram of a system that includes a switch-mode power supply coupled to an alternating current power source and a direct current power source. 
           [0008]      FIG. 2  a schematic diagram of a synchronous brushless generator with a shunt-connected voltage regulator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    The methods, systems, and apparatus described herein facilitate providing a switch-mode power supply with a dual primary transformer such that power can be supplied to an electronic voltage regulator even if power is not being received from an alternating current (AC) power source. Electronics power supply cost is reduced by requiring only one transformer to perform the necessary electrical isolation and voltage transformation from either the AC power source or the DC power source. 
         [0010]    Embodiments of the present disclosure enable an electronic voltage regulator to perform temperature monitoring (or other system variable monitoring) and to communicate this monitoring data over a communication network, even when an AC power source, such as a generator, is not rotating. As such, the present disclosure enables a switch-mode power supply to power electronics from either a relatively high voltage of a permanent magnet generator (PMG) if the PMG is rotating, or from a DC power source, such as a 12 volt or 24 volt battery, if the PMG is at rest. Further, the present disclosure achieves this with only one transformer. This idea can be extended to other applications other than voltage regulators where transformation and isolation from multiple power sources of disparate voltage ratings are used. 
         [0011]    Further, when the additional cost or physical size impact of a PMG is undesirable in an excitation system of a particular AC power source, such as a brushless synchronous generators, a “shunt powered” voltage regulator is often used. With such a voltage regulator, the source of excitation power used to drive current into an exciter field is derived directly from the output voltage of the generator itself. The power input to the regulator is connected in parallel or in “shunt” with the main output of the generator. During the start-up process of such an excitation system, the regulator may be required to drive a current into the exciter even when a very low voltage has developed across the output of the main generator. Such a requirement can be viewed as a “bootstrapping” operation, whereby the regulator uses a small amount of residual voltage available at the generator output and converts it to a DC excitation current of sufficient amplitude to build up the generator voltage. Such a process is regenerative and usually works except in cases where the residual voltage is simply too low. In such cases, the exciter field can be “flashed” by temporarily connecting a 12 volt or 24 volt battery across it. Such a flashing action will induce enough residual magnetism in an exciter field magnetic core to successfully bootstrap the voltage when using a shunt-connected regulator. Prior art circuitry used for exciter field flashing is typically complex and bulky (usually made up of manual switches and electromechanical relays). Embodiments of the present disclosure automatically generate a source of stored energy that is derived from a battery, but is also electrically isolated from the battery. This stored energy is used to flash the exciter circuit, and once generator voltage build-up is initiated, the electronic voltage regulator is enabled to seamlessly assume control of the voltage regulator process, without the need of electromechanical relays or switches. 
         [0012]      FIG. 1  is a schematic diagram of a system  100  that includes a switch-mode power supply  102  coupled to an alternating current (AC) power source  104  and a direct current (DC) power source  106 . Switch mode power supply  100  includes a transformer  108  (e.g., a dual primary flyback transformer). Primary windings  110  and  112  of transformer  108  are each driven in a conventional manner, each with its own switch-mode control circuit,  114  and  116 . A main output  118  of switch-mode power supply  100  is derived from transformer secondary winding  120 . Main output  118  is a primary source of low voltage power (e.g., between 3.3 volts and 15 volts) for utilization by the control electronics of the voltage regulator  202  described below with respect to  FIG. 2 . From main output  118 , several other power supply voltages may be derived by the use of downstream linear or switch-mode voltage converters (not shown). 
         [0013]    Alternating current (AC) power source  104  may be a permanent magnet generator (PMG) or a brushless synchronous generator that provides a voltage, for example, between 100 volts to 300 volts. Direct current (DC) power source  106  may be a DC battery with a voltage of, for example, 8 volts to 32 volts. Embodiments of the present disclosure enable either AC power source  104  or DC power source  106  to drive one of primary windings  110  and  112  of transformer  108 . 
         [0014]    With respect to AC power source  104 , a bridge rectifier  124  converts an alternating current of AC power source  104  to a direct current. Filter capacitor  126  smoothes the voltage ripples of the output of bridge rectifier  124 . Resistor  128  provides switch-mode control circuit  114  with a small amount of bias current which is necessary for switch-mode control circuit  114  to initiate its control function. Switch-mode control circuit  114  accepts a feedback voltage signal  130  from the rectified and filtered output of tertiary winding  122 . The regulating action of switch-mode control circuit  114  drives a gate voltage signal  132  in a pulse-width modulated fashion in such a way as to cause feedback voltage signal  130  to match an internal reference voltage. The topology of primary winding  110  and secondary winding  120  and tertiary winding  122  are that of the flyback converter well-known to those skilled in the art of switch-mode power supply design. When current in primary winding  110  is interrupted by transistor  134 , the magnetic coupling between primary winding  110 , secondary winding  120 , and tertiary winding  122  causes a flyback voltage to appear at secondary windings  120  and tertiary winding  122 , which in turn builds up a charge at capacitors  123  and  125 . Thus, secondary winding  120  develops a DC voltage on capacitor  125  (e.g., 5 volts) and tertiary winding  122  develops a DC voltages on capacitor  123  (e.g., 15 volts). Voltage from capacitor  123  are thereafter sensed by feedback voltage signal  130 , which is fed to switch-mode control circuit  114 . Switch-mode control circuit  114  controls gating of transistor  134  to ensure that a desired voltage is produced at auxiliary output  119 . In addition to providing voltage feedback, signal  130  may be used to provide circuit power to switch-mode control circuit  114 . By virtue of regulating voltage at auxiliary output  119 , the flyback voltage action of secondary winding  120  produces a DC voltage across output capacitor  125 . Transformer  108  turns ratio is so designed that main output  118  produces a proper utilization voltage (e.g., 5 volts) when auxiliary output  119  is regulated to its designed set-point value (e.g., 15 volts). During the active, or ON phase of transistor  134 , a voltage is produced at primary winding  112  due to magnetic coupling of primary windings  110  and  112 . The polarity of the voltage at primary winding  112  during the ON phase of transistor  134  forward biases diode  136  and causes a DC voltage to build up on capacitor  140 . This action will be recognized to those skilled in the art of switch-mode power supply design as that of a forward converter. The DC voltage produced across capacitor  140  is available for utilization in the electronics module if desired. Further, the turns ratios of primary windings  110  and  112  are such that secondary winding  120  and tertiary winding  122  receive the same amount of voltage on flyback voltage conversion from either AC power source  104  or DC power source  106 . 
         [0015]    It is not desirable for switch-mode control circuits  114  and  116  to be active at the same time. Rather, only control circuit  116  is active when DC power source  106  is connected. This permits an electronic module (not shown) supplied by main output  118  to be active even when AC power source  104  is not active, for example, when AC power source  104  is a PMG at a standstill. The presence of DC power source  106  produces a logic-level signal  142  across voltage clamping diode  144 . Signal  142  feeds the input of interlock signal isolator  146 . Interlock signal isolator  146  provides electrical isolation between signal  148  and signal  150  while passing the interlock logic information to switch-mode control circuit  114 . Signal  150  is fed into the SHUTDOWN input of switch-mode control circuit  114 , deactivating switch-mode control circuit  114  when DC power source  106  is present. When DC power source  106  is not present, a zero voltage level is present at signal  142 . Signal  142  is fed to inverting buffer  152  and its output signal  154  is fed into the SHUTDOWN input of switch-mode control circuit  116 , deactivating switch-mode control circuit  116 . In one embodiment, a selection of a power source is automatic based on the presence or absence of a rotation from a main generator associated with the PMG. 
         [0016]    With respect to DC power source  106 , filter capacitor  140  acts as a bypass energy source to DC power source  106 . Resistor  156  provides switch-mode control circuit  116  with a small amount of bias current which is necessary for switch-mode control circuit  116  to initiate its control function. Switch-mode control circuit  116  accepts a feedback signal  158  from the rectified and filtered output of secondary winding  120 . The regulating action of switch-mode control circuit  116  drives the gate voltage signal  160  in a pulse-width modulated fashion in such a way as to cause feedback signal  158  of main output  118  to match an internal reference voltage of control circuit  116  (e.g., 5 volts). The topology of primary winding  112  and secondary windings  120  and tertiary winding  122  are that of the flyback converter well-known to those skilled in the art of switch-mode power supply design. When current in primary winding  112  is interrupted by power transistor  162 , the magnetic coupling between primary windings  112  and secondary winding  120  and tertiary winding  122  causes a flyback voltage to appear at secondary winding  120  and tertiary winding  122 . The regulating action of switch-mode control circuit  116  ensures that the desired voltage is produced at main output  118 . By virtue of regulating voltage at main output  118 , the flyback voltage action of tertiary winding  122  produces a DC voltage across output capacitor  123 . Transformer  108  turns ratio is so designed that auxiliary output  119  produces a proper utilization voltage (e.g., 15 volts) when main output  118  is regulated to its designed set-point value (e.g., 5 volts). During the active, or ON phase of transistor  162 , a voltage is produced at primary winding  110  due to magnetic coupling of primary windings  110  and  112 . The polarity of the voltage at primary winding  110  during the ON phase of transistor  162  forward biases diode  138  and causes a voltage to build up on capacitor  126 . This action will be recognized to those skilled in the art of switch-mode power supply design as that of a forward converter. The DC voltage produced across capacitor  126  is available for utilization in the electronics module if desired. The forward converter action and turns ratio of transformer windings  110  and  112  are such that a DC voltage of several multiples of that of DC power source  106  may be developed across capacitor  126 . In particular, the energy stored across capacitor  126  can be used as a source of flashing current to magnetize the exciter stator core in a brushless synchronous generator to assist in the voltage build-up process of a shunt-fed voltage regulator as described below with reference to  FIG. 2 . 
         [0017]    With reference now to  FIG. 2 , a schematic diagram of a synchronous brushless generator (e.g., AC power source  104  as shown in  FIG. 1 ) with a shunt-connected voltage regulator  202 . Exciter field winding  204  is magnetically coupled by exciter magnetic core  206  to exciter rotor winding  208 . Exciter rotor winding  208 , exciter rotating rectifier  210 , and generator main field winding  212  are mounted on a rotating shaft (not shown) of AC power source  104 . The magnetic field produced by current in main field winding  212  is coupled to a main armature  213  of AC power source  104  by magnetic core  214 . Mechanical rotation of a current-carrying main field winding  212  produces a rotating magnetic flux wave in magnetic core  214 . Rotating flux wave magnetic core  214  induces alternating current voltage sources  216 ,  218 , and  220  in armature  213  of AC power source  104 . As can be deduced by the above explanation, current in exciter field winding  204  is a prerequisite to induce voltage at generator terminals  222 ,  224 ,  226 . 
         [0018]    During the voltage build-up phase of AC power source  104  when a rotation of a shaft (not shown) of AC power source  104  has commenced, there is no current existing in exciter field winding  204 . There exists a relatively small voltage at generator terminals  222 ,  224 , and  226  due to a residual magnetism in exciter core  206  and generator core  214 . Conventionally, voltage regulator  202  is dependent upon residual magnetism of AC power source  104  to produce enough voltage across the output of rectifier  124  to enable voltage regulator control circuit  230  to operate. Output electronic switch  232  is required to be in an ON or CLOSED state to cause current to flow in exciter field winding  204 . If insufficient voltage is available at the output of rectifier  124 , control circuit  230  will fail to turn electronic switch  232  ON and voltage build-up of AC power source  104  will fail to happen. A conventional solution to the low residual voltage build-up problem described above has been addressed by “flashing” or temporarily connecting a battery (e.g., a 12 volt or a 24 volt battery) across exciter field winding  204 . This process in normally a manual one used for relatively small, portable generators of the type used for standby or temporary sources of AC power. More complex switching circuits of varying complexity are sometimes built into the engine-generator sets that automatically detect the need for field flashing and perform an automated, temporary application of battery power to exciter field winding  204 . Such circuits require add-on equipment such as voltage sensing circuitry and electromechanical relays for application and removal of battery power to the exciter field winding. The brief application of current into the exciter field winding  204  usually induces sufficient residual magnetism to allow the shunt-connected voltage regulator  202  to successfully build up generator voltage. 
         [0019]    Embodiments of the present disclosure overcome the failure-to-build voltage problem of shunt-connected voltage regulators through the implementation of a switch-mode power supply  100  shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , rectifier  124  and capacitor  126  are common elements in both the power supply circuit of  FIG. 1  and voltage regulator circuit  202  of  FIG. 2 . For illustrative purposes, a single phase AC power source  104  of  FIG. 1  is replaced by a line-to-line voltage of a three-phase AC generator  104  in  FIG. 2 , while the remaining components of  FIG. 1  remain intact. 
         [0020]    Application of DC power source  106  produces a logic-level main output power supply  118  that is available for utilization by regulator control circuit  230 . Regulator control circuit  230 , having logic-level voltage  118  available, is enabled to monitor the status of AC power source  104  voltage with output of voltage attenuation circuit  234 . Attenuation circuit  234  presents a very high input impedance (greater than one meg-ohm) to provide impedance isolation between AC power source  104  and regulator control circuit  230 . By monitoring the status of a voltage of AC power source  104 , regulator control circuit  230  can determine if AC power source  104  is rotating by monitoring a frequency of its residual voltage. Should regulator control circuit  230  determine that AC power source  104  is rotating, regulator control circuit  230  can begin pulsing an exciter current into exciter field winding  204  to begin the voltage build-up process. Conventionally, there would be an insufficient source of excitation energy if residual voltage of AC power source  104  was too low. However, embodiments of the present disclosure, with DC power source  106  connected, produce a stepped up voltage across capacitor  126 , as a result of winding design of transformer  102  (shown in  FIG. 1 ). The voltage produced across capacitor  126  by the power supply of  FIG. 1  equates to an amount of stored energy that is available for the flashing of exciter field winding  204 . Upon detection of generator rotation as described above, regulator control circuit  230  can apply current from the stored charge on capacitor  126  to exciter field winding  204  by controlling a gate signal  236  to electronic switch  232  through the gate signal opto-isolator  240 . A Hall-effect linear current sensor with input-to-output galvanic isolation  241  or other suitable current sensor with electrical isolation is used to provide an exciter field winding current feedback signal to regulator control circuit  230  to enable control of current in exciter field winding  204 . 
         [0021]    As mentioned above, transformer  108  (shown in  FIG. 1 ) provides an electrical isolation between DC power source  106  (shown in  FIG. 1 ) and a voltage regulator circuit  202 . This is shown by ground circuit reference  168  of the battery circuit and the circuit reference potential  166  derived from AC source  104  of both  FIGS. 1 and 2 . From  FIG. 2 , it is apparent that circuit reference potential  166  is derived from the DC rectified output of the high voltage AC terminal voltage of AC power source  104 . The electrical isolation provided by transformer  102  (shown in  FIG. 1 ), signal isolator  146  (shown in  FIG. 1 ), attenuation circuit with impedance isolation (shown in  FIG. 2 ), gate signal opto-isolator  240  (shown in  FIG. 2 ) and Hall-effect linear current sensor with galvanic isolation  241  (shown in  FIG. 2 ) are critical in conforming to safety codes that require electrical isolation between low voltage control circuits, such as those derived from DC power source  106 , and high voltage power circuits, such as those derived from AC power source  104 . 
         [0022]    The methods, systems, and apparatus are not limited to the specific embodiments described herein, but rather, components of each apparatus, as well as steps of each method, may be utilized independently and separately from other components and steps described herein. Each component, and each method step, can also be used in combination with other components and/or method steps. Furthermore, although described herein with respect to an electric generator, the methods, systems, and apparatus described herein are applicable to all electric machines, including electric motors and electric generators. 
         [0023]    Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
         [0024]    When introducing elements/components/etc. of the systems and apparatus described and/or illustrated herein, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc. 
         [0025]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.