Abstract:
A system and method are disclosed for regulating a generator controlled power signal. An exemplary embodiment of the system may include both a digital voltage regulator and an analog voltage regulator and a selector switch configured to switch modulation control between the digital and analog voltage regulators. A watchdog detection circuit may be included for detecting an upsetting event in the digital voltage regulator and may trigger switching of the generator excitation input voltage modulation from the digital voltage regulator to the analog voltage regulator. An exemplary embodiment of the method may include modulating the generator excitation input voltage using the digital voltage regulator, detecting an occurrence of an upsetting event in the digital voltage regulator, disabling the digital voltage regulator, and switching modulation of the generator excitation input voltage to the analog voltage regulator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to generator control systems and more particularly, to aircraft voltage regulators. 
         [0002]    It is known for generator control systems in aircraft to implement software-based digital control mechanisms like RMS voltage control, compensation for PMG voltage in variable frequency systems. 
         [0003]    Referring to  FIG. 1 , a prior art configuration illustrates a typical software-based voltage control using a digital voltage regulation system  110 . As shown in  FIG. 1 , analog control feedback signals  105  are conditioned in a signal conditioning unit  111  and converted to digital in an analog to digital converter  112 . The feedback signals  105  may then be fed to a digital control  115  for compensation control. The control algorithm that may be used varies depending on the application and desired effectiveness of control. Based on the control algorithm, the digital processor  119  commands the digital control  115  to generate a gating signal to a gate driver  135  and a field modulation switch  137  to perform pulse width modulation (PWM) on the generator excitation voltage supply. Therefore the generator field excitation current is adjusted dynamically to minimize the voltage variation at the point of regulation at different operating conditions. 
         [0004]    In some cases software-based control using digital voltage regulation may be susceptible to Single/Multiple Event Upsets (SEU) and indirect effects from lightning. Such effects may cause a microprocessor or digital signal processor  119  to reset or stop functioning. During this time, all devices connected to the power system may temporarily shutdown and require a few seconds to get back into the original operating state. These types of events could incur serious workload issues for the aircraft electrical power systems and potentially have dangerous results for pilots flying the aircraft. 
         [0005]    As can be seen, there is a need for a generator regulator system that can function during temporary interruption of regulation. 
       SUMMARY OF THE INVENTION 
       [0006]    In one aspect of the present invention, a voltage control system, comprises a digital voltage regulator enabled and configured to produce a digital gating signal to modulate a field current; an analog voltage regulator, pre-set disabled and configured to produce an analog gating signal to modulate the field current; and a selector switch coupled between the digital voltage regulator and the analog voltage regulator, wherein the selector switch is configured to cease a transmission of the digital gating signal from the digital voltage regulator upon detection of an upsetting event in the digital voltage regulator and further configured to enable transmission of the analog gating signal from the analog voltage regulator to the field current. 
         [0007]    In another aspect of the present invention, a voltage regulator circuit, a digital voltage regulator enabled and configured to produce a digital gating signal to modulate a field current; an analog voltage regulator, pre-set disabled and configured to produce an analog gating signal to modulate the field current; a selector switch coupled between the digital voltage regulator and the analog voltage regulator, wherein the selector switch is configured to cease a transmission of the digital gating signal from the digital voltage regulator upon detection of an upsetting event in the digital voltage regulator and further configured to enable transmission of the analog gating signal from the analog voltage regulator to the field current; and a watchdog detection circuit coupled to the selector switch and the digital voltage regulator for detecting an upsetting event in the digital voltage regulator, wherein the watchdog detection circuit transmits a command signal to the selector switch to disable transmission of the digital gating signal from the digital voltage regulator and enable transmission of the analog gating signal from the analog voltage regulator. 
         [0008]    In a further aspect, a method of regulating a power signal from a generator, comprises the steps of generating a gating signal using a digital voltage regulator to modulate an excitation input voltage of the generator; detecting an occurrence of an upsetting event in an operation of the digital voltage regulator; disabling the digital voltage regulator; and modulating the excitation input voltage from the generator using an analog voltage regulator. 
         [0009]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic depicting a prior art generator control circuit; 
           [0011]      FIG. 2  is a schematic illustrating a generator control system in accordance with an exemplary embodiment of the present invention; 
           [0012]      FIG. 3  is a graph illustrating an exemplary signal transition from a digital voltage regulator to an analog voltage regulator in accordance with an exemplary embodiment of the present invention; 
           [0013]      FIG. 4  is a graph illustrating an exemplary reset of a signal from an digital voltage regulator in accordance with an exemplary embodiment of the present invention; and 
           [0014]      FIG. 5  is a flowchart depicting an exemplary series of steps in a method in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0016]    Various inventive features are described below that can each be used independently of one another or in combination with other features. 
         [0017]    Broadly, embodiments of the present invention generally provide a voltage control system for re-directing transmission of a gating signal during digital processor upsets. In general, exemplary embodiments of the voltage control system of the present invention may provide a digitally controlled pulse width modulation of a generator excitation voltage under uninterrupted conditions with an expedient transition to an analog controlled pulse width modulation of the generator excitation voltage should an upsetting event occur. In an exemplary use, embodiments of the voltage control system may be used in aircraft where, during a lightning strike, a digital processor in the digitally controlled portion of the system may be reset or damaged to failure by the effects of the lightning. In one aspect, the voltage control system monitors the digitally controlled portion for an interruption in the operation of the processor, switches regulation from the digitally controlled portion to an analog controlled portion, thus maintaining uninterrupted modulation of the excitation input voltage from the generator control unit. 
         [0018]    Referring now to  FIG. 2 , a voltage control system  200  is depicted showing a proposed exemplary circuit scheme. The voltage control system  200  generally may include a digital voltage regulator  210 , an analog voltage regulator  220 , and a regulator selector  230 . The voltage control system  200  may also include a watchdog detection circuit  250 , a field current modulation switch  237 , a gate driver  235 , a driver module  234  for regulator selector, a time delay circuit  255 , and a hardware protection circuit  260 . Feedback signals  205  may be transmitted from a point of regulation (not shown) into the control system  200 . The feedback signals  205  may include a voltage point of regulation feedback signal  202 , a generator current signal  204 , and a field current signal  206 . The voltage point of regulation feedback signal  202  and the field current signal  206  may each include three lines respectively. 
         [0019]    The digital voltage regulator  210  may include a digital processor  219  that perform digital control  215 , a signal conditioning circuit  211 , an analog to digital converter  212 , a voltage reference module  216 , and a reset switch  214 . The digital processor  219  may produce a watchdog toggle signal  213  that may be monitored by the watchdog detection circuit  250 . 
         [0020]    The analog voltage regulator  220  may include an analog control  225 , peak voltage conditioning circuits  221  a and  221  b, a reference module  227 , and a filter  223 . 
         [0021]    An exemplary circuit employing the above-described elements may be connected as follows. The field current modulation switch  237  may, for example, be a MOSFET connected on a generator field winding  236 . A field free wheeling diode  239  maintains the field excitation current in a generator field winding  236  o be continuous when the field current modulation switch  237  is off. An opposite element of the field current modulation switch  237  provides a modulated field current back to the excitation power supply (not shown). An intermediate element of the field current modulation switch  237  may be connected to a gate driver  235  receiving a gating signal from the digital voltage regulator  210  or the analog voltage regulator  220 . The gate driver  235  may also be connected to a regulator selector  230 . The regulator selector  230  may be a switch-type device opening and closing line contacts between the gate driver  235  and the digital voltage regulator  210  or analog voltage regulator  220 . In this exemplary embodiment, the regulator selector  230  is configured to transmit a digital gating signal from the digital voltage regulator  210  during normal operation. The regulator selector  230  is also configured to transmit an analog gating signal from the analog voltage regulator  220  during interruption of the digital voltage regulator  210 . The watchdog detection circuit  250  may be connected to both the digital voltage regulator  210  and analog voltage regulator  220 . The time delay circuit  255  may be connected to the analog voltage regulator  220  and to the hardware protection circuit  260 , which in turn may be connected to a shutdown mechanism (not shown) capable of powering down the generator (not shown). Additionally, a driver module  234  may be connected between the watchdog detection circuit  250  and the regulator selector switch  230 . The driver module  234  may provide command signals to open and close the regulator selector  230  and so that either the analog voltage regulator  220  or the digital voltage regulator  210  is connected to the gate driver  235  of the field current modulation switch  237  as desired. 
         [0022]    Referring to  FIGS. 2 and 5 , under one exemplary operation, the voltage control system  200  may be configured with the regulator selector  230  creating a closed line contact with the digital voltage regulator  210  so that the digital voltage regulator is enabled for producing digital gating signals to the field current modulation switch  237  (Step  505 ). In step  510 , feedback signals  205  may be received by the signal conditioning circuit  211 . The feedback signals  205  may be conditioned and then may be transmitted to the analog to digital converter  212 . The analog to digital converter  212  may convert the feedback signals  205  to a digital signal for receipt by the digital controller  215 . The digital controller  215  may perform actions under the direction of the digital processor  219 . Actions may include checking the digital signal for signal levels against stored threshold levels in the voltage reference module  216  and transmitting the digital signal to the gate driver  235  through the regulator selector  230 . The gate driver  235  may transmit the digital gating signal to the field current modulation switch  237 . Additionally, the digital processor  219  may produce an oscillating waveform signal, a watchdog toggle signal  213 , which may be monitored and evaluated by the watchdog detection circuit  250 . 
         [0023]    The regulator selector  230  may have an open contact line with the analog voltage regulator  220  when the digital voltage regulator is operational. The analog voltage regulator  220  may be pre-set as disabled or inoperative by setting a setpoint in its voltage reference in the reference module  227  to zero. Therefore, the analog voltage regulator  220  may not produce gating since the feedback signals  205  signal levels may be greater than the setpoint. In some applications, the analog voltage regulator  220  may not be required to operate in current/power limit mode, and thus, in one exemplary embodiment, the generator current feedback signal  204  may not need to be connected to the analog voltage regulator  220 . Thus, an analog voltage regulator with less connections offers a simplified GCU design. 
         [0024]    Under uninterrupted operating conditions, the regulator selector  230  may be at a default position passing the gating signal of the digital voltage regulator  210  to the field current modulation switch  237 . In Step  515 , when the digital processor  219  experiences an upsetting event and stops functioning or is toggled off, the normally oscillating watchdog toggle signal  213  from the processor may become flat. Upsetting events may include for example, single or multiple event upsets, and lighting strike damage/overloads. The flattened watchdog toggle signal  213  may quickly be detected by the watchdog detection circuit  250 . In response, voltage control system  200  may take steps to transition production of the gating signal from the digital voltage regulator  210  to the analog voltage regulator  220 . 
         [0025]    The watchdog detection circuit  250  may produce a watchdog detection (or AVR Enable) discrete signal that can be either high or low depending on the design convenience. In step  535 , upon detection of an upsetting event in the digital voltage regulator  210 , the watchdog detection signal may enable the reference module  227  of the analog voltage regulator  220  to adjust the point of reference from zero to a predetermined voltage enabling operation of the analog voltage regulator  220 . The analog voltage regulator  220  may then start to generate the pulse width modulation gating signal based on the feedback signals  205 . The analog control can be active within  200  micro seconds of enablement of the analog voltage regulator  220 . In Step  520 , the watchdog detection circuit  250  may also send a command to the driver  234  triggering the regulator selector  230  to switch gating feed over to the analog voltage regulator  220  from digital voltage regulator  210 . In Step  535 , the conditioned signals in  221 a and  221 b may be transmitted to the filter  223 . Filtered signals may then be received by the analog control  225  which produces the analog gating signal that is transmitted through the regulator selector  230  into the gate driver  235 . 
         [0026]      FIG. 3  depicts a simulated signal transient  300  of a watchdog detection signal trace  310 , a digital voltage regulator gating signal trace  320 , an analog voltage regulator gating signal trace  330 , and a voltage trace  340  at the point of regulation. (POR) The signal transient  300  shows a point of regulation voltage transient during the transition from digital to analog control. In this simulated performance of the voltage control system  200 , once the watchdog detection signal is high and the digital voltage regulator  210  gating signal stops, the analog voltage regulator  220  gating signal starts modulating in about 2 milli-seconds. The POR voltage signal trace  340  drops from 350V to 305V peak (215 Vrms equivalent), which is well above commonly used voltage transient requirements. 
         [0027]    At the same time when the watchdog detection circuit  250  sends the watchdog detection signal, it may also issue a discrete signal to the reset switch  214  to reset the digital processor  219  (Step  525 ). If there is no other failure in the digital processor  219 , in other words, if the processor resumes producing oscillating signals (Step  540 ), then the digital processor will start the reset process of generating a gating signal. In Step  545 , the analog voltage regulator may be disabled and the regulator selector switch  230  may switch position to enable digital gating signals received from the digital voltage regulator  210 . 
         [0028]    In addition to the actions described above, the analog voltage regulator  220  enabling signal may also be logged by the time delay circuit  255  (Step  530 ). The time delay circuit  255  may have a pre-set time delay that is sufficient to allow the digital processor  219  to be reset in an orderly manner during analog voltage regulation. The duration of the time delay depends on the application and can be as long as several seconds. In Step  555 , if the time limit for the time delay is not reached, the count continues in Step  565  and operation of the analog voltage regulator  220  continues. If the digital processor  219  resets successfully, the watchdog toggle signal  213  will resume normal oscillation. Once the digital processor  219  is functional again, it may start the control computation and generate the pulse width modulation gating signal. When the watchdog detection circuit  250  detects the normal watchdog toggle signal  213 , the watchdog detection circuit  250  will flip which will send a signal turning the regulator selector switch  130  off. In other words, the regulator selector  230  may open the contact line to the analog voltage regulator  220  and close the contact line to the digital voltage regulator  210  to allow digital control of the gating signal to pass to the field current modulation switch  237 . At the same time the watchdog detection circuit  250  may reset the time delay circuit  255  (Step  550 ). 
         [0029]      FIG. 4  depicts a simulated transient during transition of the gating signal from the analog voltage regulator  220  to digital voltage regulator  210 . A simulated signal transient  400  of a watchdog detection signal trace  410 , a digital voltage regulator signal trace  420 , an analog voltage regulator signal trace  430 , and a POR voltage signal trace  440  depicts the watchdog detection signal trace  410  dropping from high to low, signaling a reset of the digital processor  219  and of the digital voltage regulator  210 . The POR voltage trace  440  drops a little more than that of the POR voltage  350  ( FIG. 3 ) in the transition from the digital to analog control because it may take more time for the digital control function to return to normal due to the reset process. However, the voltage is maintained and the transient meets stringent power quality requirements seen in the aerospace industry. 
         [0030]    If the digital processor  219  fails to recover when the end of time delay is reached (Step  555 ), a hardware protection circuit  260  may be activated. In Step  570 , the function of the hardware protection circuit  260  may include executing an orderly shut-down of the generator control unit which may include de-energizing the generator, taking the generator off line by opening the generator line contactor and informing aircraft of the fault. 
         [0031]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.