Abstract:
A method for controlling a turbine engine generator set is disclosed. The method comprises: sensing an operating parameter indicative of a load increase on the turbine engine generator set; operating the turbine engine generator set in a first mode when the sensed operating parameter is within a predetermined range; and operating the turbine engine generator set in a second mode when the sensed operating parameter is outside the predetermined range. The second mode provides a rate of adjustment of operation of the turbine engine generator set that is greater than a rate of adjustment during the first mode.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a system and method for controlling a gas turbine engine generator set. 
       BACKGROUND 
       [0002]    Gas turbine engine generator sets are often used in industrial systems, such as heating, cooling, food processing, etc., and provide electrical power for consumption by electrical equipment, such as electric motors or lighting systems. Depending on the operation of driven equipment, the electrical power drawn from a generator set often varies, thereby changing the electrical load of the generator set. 
         [0003]    U.S. Pat. No. 4,380,894 discloses a fuel supply control system for a turbine engine. The system determines a fuel flow demand based a speed of a compressor shaft and an engine load. When the load applied to the engine is increased, the system increases the fuel flow demand to increase torque applied to the turbine output shaft and thereby maintains a speed of the output shaft within a given range. 
       SUMMARY 
       [0004]    In some embodiments, a method for controlling a turbine engine generator set is disclosed. The method comprises: sensing an operating parameter indicative of a load increase on the turbine engine generator set; operating the turbine engine generator set in a first mode when the sensed operating parameter is within a predetermined range; and operating the turbine engine generator set in a second mode when the sensed operating parameter is outside the predetermined range. The second mode provides a rate of adjustment of operation of the turbine engine generator set that is greater than a rate of adjustment during the first mode. 
         [0005]    In some alternative embodiments, a system for controlling a turbine engine generator set is disclosed. The system comprises one or more sensors configured to sense an operating parameter indicative of a load increase on the turbine engine generator set. The system further comprises a controller configured to operate the turbine engine generator set in a first mode when the sensed operating parameter is within a predetermined range and to operate the turbine engine generator set in a second mode when the sensed operating parameter is outside the predetermined range. The second mode provides a rate of adjustment of operation of the turbine engine generator set that is greater than a rate of adjustment during the first mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an illustration of an exemplary disclosed control system for controlling a gas turbine engine generator set; and 
           [0007]      FIG. 2  illustrates an exemplary process for controlling a gas turbine engine generator set. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIG. 1  illustrates an exemplary disclosed control system  100  for controlling a gas turbine engine generator set  110 , in accordance with one embodiment. 
         [0009]    In particular, gas turbine engine generator set  110  includes a compressor  112 , a combustor  114 , a turbine  116 , and an electrical generator  118 . Compressor  112  receives an incoming gas flow  111 , compresses the gas to increase the pressure and temperature thereof, and provides the compressed gas to the combustor  114 . Combustor  114 , also known as combustion chamber or burner, receives the compressed gas flow  113  from compressor  112 , and also receives fuel  109  through a fuel supply valve  108 . Combustor  114  mixes the fuel and the compressed gas and heats the compressed gas by burning the fuel therein. The burning of the fuel adds energy to the compressed gas and increases the temperature of the gas flow. Combustor  114  then provides the higher temperature gas flow  115  to turbine  116 . Higher temperature gas flow  115  drives turbine  116  and exits turbine system  110  as a lower-temperature, lower-pressure gas flow  117 . Turbine  116  is coupled with compressor  112  through a compressor shaft  130 . When driven by gas flow  115 , turbine  116  rotates and drives compressor  112  through shaft  130 . Turbine  116  is further coupled to generator  118  and drives generator  118  through an output shaft  132 . 
         [0010]    Compressor  112  may be an axial compressor including a plurality of stages. Each stage includes rotational blades or airfoils  136  driven by shaft  130 , and stationary vanes  134  mounted on a compressor casing. The stationary vanes  134  guide the incoming gas flow onto the blades  136 , while shaft  130  drives the rotational blades to move the gas in an axial direction to a next stage where the gas is further compressed. Compressor  112  may include a set of inlet guide vanes  134  mounted on the compressor casing in front of the first stage of compressor  112 . Inlet guide vanes  134  direct incoming gas flow  111  onto a set of first-stage blades  136 . First-stage blades  136  are driven by shaft  130  and move incoming gas flow  111  to the subsequent stages. 
         [0011]    Each inlet guide vane  134  is mounted on a rotational shaft and may be rotated as desired. By positioning inlet guide vanes  134  at different angles, incoming gas flow  111  may be directed in different directions onto rotational blades  136  of the first stage of compressor  112 , thereby controlling operational characteristics of turbine engine generator set  110 , such as the rotational speed of shaft  130  and the output power of generator  118 . 
         [0012]    Generator  118  may be a DC generator or an AC generator known in the art. The output terminal of generator  118  is coupled to an electrical equipment  122  through output lines  119  so that generator  118  provides electrical power to drive equipment  122  or any other types of devices or systems configured to receive electrical power. Electrical equipment  122  may be a motor, a power mill, a heat pump, an electrical compressor, etc. Electrical equipment  122  draws electrical power from generator  118 , thereby imposing electrical loads thereon. As a result, an electrical current flows in output lines  119  between generator  118  and electrical equipment  122 , corresponding to the electrical loads provided to equipment  122 . In general, the greater the electrical load drawn from generator  118 , the greater the electrical current in output lines  119   
         [0013]    According to a further embodiment, gas turbine engine generator set  110  is an integrated system, which is provided to a customer for producing electrical power. Compressor  112 , combustor  114 , turbine  116 , and generator  118  may be assembled within an integrated package and coupled to electrical equipment  122 . As such, generator set  110  provides a simple and integrated electrical power source, which enhances reliability and reduces maintenance costs. 
         [0014]    Control system  100  includes a controller  106  for monitoring operational states and controlling operation of turbine engine generator set  110 . For example, controller  106  may monitor status parameters, such as the output power of generator set  110 , the rotational speed of shaft  130 , or any other parameters necessary to control the generator set  110 . Based on the status parameters, controller  106  may set control parameters, such as the fuel supply rate, the inlet guide vane angle, or the output voltage level. Alternatively, controller  106  may provide warning or shut down generator set  110  if the operational temperature exceed a threshold temperature value. 
         [0015]    Control system  100  further includes a speed sensor  124  and a power sensor  128  configured to provide input signals to controller  106 . The input signal may reflect the rotational speed of shaft  130  and the electrical load drawn by equipment  122 , respectively. Based on the input signals, controller  106  determines a proper fuel supply rate, an output voltage level, and an inlet guide vane angle, and generates control signals  101 ,  117 , and  126  to set the fuel supply rate, the output voltage level, and the inlet guide vane angle, respectively. In general, when the electrical load increases, controller  106  tends to increases the fuel supply rate and the inlet guide vane angle. 
         [0016]    Sensor  124  is a speed sensor for measuring the rotational speeds of compressor shaft  130 . Alternatively, sensor  124  may be associated with output shaft  132  to measure the rotational speed thereof. Sensor  124  may be a magnetic sensor or a hall effect sensor known in the art. Sensor  124  converts the rotations of shaft  130  into an electronic signal  120  and transmits the signal to controller  106 . Controller  106  may then determine the rotational speed of shaft  130  according to signal  120 . 
         [0017]    Sensor  128  is an electrical power sensor configured to determine the output electrical power provided by generator  118  through the output terminals thereof. Power sensor  128  may be a DC or AC load sensor, which generates a signal  107  reflecting the electrical power provided to electrical equipment  122 . For example, the power sensor  128  may determine the electrical power based on the voltage and current in output lines  119 . 
         [0018]    Controller  106  may include a fuel control module  102 , a voltage control module  103 , and a guide vane control module  104  to provide the control functions described herein. Control modules  102 - 104  may be implemented on one or more circuit modules, such as a programmable logic controller, a programmable gate array, an application specific integrated circuit, etc. Alternatively, control modules  102 - 104  may be implemented as software modules on a general-purpose computer. The computer includes suitable interfaces for receiving input signals from sensors  124  and  128  and transmitting control signals  101 ,  117 , and  126 . The software program associated with control modules  102 - 104  may be stored in a computer-readable medium as program codes. Upon being executed by the computer, control modules  102 - 104  may instruct the computer to control generator set  110  through control signals  101 ,  117 , and  126 . 
         [0019]    According to an alternative embodiment, gas turbine engine generator set  110  may include a two-shaft turbine system. Specifically, turbine  116  may include a first turbine coupled to compressor  112  through compressor shaft  130  and a second turbine coupled to generator  118  through output shaft  132 . The first turbine provides high-temperature gas flow  115  to the second turbine, thereby driving the second turbine to rotate, which then drives generator  118  through output shaft  132 . According to this embodiment, shafts  130  and  132  may rotate at different speeds. Speed sensor  124  may be associated with either shaft  130  or  132  to measure the rotational speed, and controller  106  may perform the control functions described herein based on the rotational speed of either shaft  130  or  132 . 
         [0020]    Controller  106  receives input signals from sensors  124  and  128 , determines the control parameters, and generates control signals  101 ,  117 , and  126  based on control cycles. A control cycle of controller  106  includes a recursive sequence of control steps performed within a time interval according to the control logic. For example, in each control cycle, controller  106  samples the rotational speed and the output power reflected in the input signals, and compares the sample values with those from a preceding cycle. Controller  106  may adjust the fuel supply rate, the output voltage level, or the inlet guide vane angle for the current control cycle in accordance with the comparison results. Controller  106  may perform all or part of the control steps in each control cycle according to the control logic. Each control cycle may last for, for example, about 20 milliseconds. The length of the control cycle may vary depending on the configuration of controller  106 . Further, the preceding control cycle may be immediately prior to the current control cycle or any other earlier control cycles. 
         [0021]    Controller  106  may instruct generator set  110  to operate in a plurality of modes and switch generator set  110  between different modes in accordance with the status parameters reflected in the input signals from sensors  124  and  128 . For example, controller  106  may set generator set  110  in a first mode (or a normal operating model), in which generator set  110  operates in a steady state. In the normal operating mode, controller  106  adjusts the parameters, such as the fuel supply rate, the output voltage level, and the inlet guide vane angle, continuously or in a very small increment in each control cycle. For example, when detecting an increases in the electrical load at the output of generator set  110  in a given control cycle, controller  106  may gradually increase the fuel supply rate by, for example, 1-2% from the preceding cycle. Alternatively, controller  106  may gradually decreases the output voltage level by, for example, 1-2% from the preceding cycle, in response to the increases in output load. Still alternatively, controller  106  may gradually increase the inlet guide vane angle at a rate equal to, for example, 1-2 degrees per second in response to the increases in the electrical load. 
         [0022]    Under certain conditions, controller  106  may switch generator set  110  from the first mode to a second mode (or a transient mode), in which generator set  110  responds to the increases in the electrical load much more rapidly. For example, in a given control cycle, when detecting that there is a abrupt increase in the electrical load at the output of generator set  110  compared with a preceding control cycle, controller  106  may switch generator set  110  to the transient mode. Here, an abrupt increase in the electrical load or an abrupt load increase refers to an increase by 25-50% of the total capacity of the generator set  110  compared with the electrical load in the preceding control cycle. 
         [0023]    In particular, in response to the abrupt load increase, controller  106  may increase the fuel supply rate by, for example, 5-15% from the preceding control cycle. Alternatively, controller  106  may decrease the output voltage level by, for example, 5-15% from the preceding cycle. Still alternatively, in the transient mode, controller  106  may increase the inlet guide vane angle to a fully open position at a rate of, for example, 25° per second. By switching generator set  110  from the normal operating mode to the transient mode, controller  106  allows generator set  110  to respond to the abrupt increase in the electrical load without comprising the performance of the system. 
       INDUSTRIAL APPLICABILITY 
       [0024]    The above-disclosed control system, while being described for use in a gas turbine engine generator set, can be used generally in alternative applications and environments, for example, where an abrupt increase in load is detected on the output of a generator. In general, the control system may respond to the increase in load by switching the generator set from the first mode to the second mode. The generator set operating in the second mode provides a rate of adjustment of the operation greater than a rate of adjustment in the first mode. 
         [0025]    Referring back to  FIG. 1 , the electrical power consumed by electrical equipment  122  may vary, thereby causing the electrical load at the output terminal of generator set  110  to increase or decrease. For example, electrical equipment  122  may be an electrical motor driving a conveyor belt. The electrical load imparted onto generator set  110  may increase or decrease when the weight loaded onto the conveyor belt varies. As another example, electrical equipment  122  may include electrical systems in an industrial site, such as the lighting system, the air conditioning system, the sewage system, etc. As such, the electrical power demanded from generator set  110  may increase or decrease when the usage of the electrical systems varies, such as more light bulbs being turned on or the air condition being turned up. Depending on the changes in the electrical load, control system  100  sets generator set  110  in the normal operating mode or the transient mode and switches generator set  110  between different modes as described herein. 
         [0026]      FIG. 2  depicts an exemplary disclosed process  200  for controlling turbine engine generator set  110  when a load increase is detected. Process  200  may be implemented on control system  100  through controller  106  and modules  102 - 104  included therein. 
         [0027]    According to process  200 , at step  202 , control system  100  senses an operating parameters indicative of a load increase. As discussed above, control system  100  may perform the control functions based on control cycles and sample the input signals, including the rotational speed and the electrical load, in each control cycle. Based on the input signals ( 107 , 120 ), control system  100  adjusts the control parameters, if necessary, in each control cycle. 
         [0028]    Further, at step  202 , control system  100  determines whether a load increase is detected based on the operating parameters collected at each control cycle. According to some embodiments, control system  100  may detect the load increase through signal  107  from load sensor  128 . Load sensor  128  transmits load signal  107  to controller  106 , which reflects the electrical load or power drawn from generator set  110  through output lines  119  in the current control cycle. 
         [0029]    Alternatively or additionally, controller  106  may detect the load increase based on the speed signals from speed sensor  124 . Specifically, controller  106  samples speed signal  120  from sensor  124  in each control cycle and compares the speed signal in the current cycle with a speed signal received in the preceding cycle. 
         [0030]    Controller  106  may also detect the load increase according to a fuel command that controller  106  generates as part of the control scheme in the normal operating mode. Specifically, when a load increase occurs, controller  106 , in the normal operating mode, may attempt to respond to the load increase and thus generate a fuel command to instruct fuel valve  108  to increase the fuel supply rate. Thus, by checking the fuel command, controller  106  may detect whether a load increase has occurred at the output of generator set  110 . 
         [0031]    At step  204 , control system  100  may determine whether the detected load increase is within the predetermined range. For example, controller  106  may compare load signal  107  collected in the current control cycle with load signals received in a preceding cycle. If a difference between the electrical load reflected by load signal  107  and the electrical load in the preceding cycle exceeds a threshold load value, controller  106  determines that an abrupt load increase has been added to the output of generator set  110  or that the load increase exceeds the predetermine range. In other words, controller  106  determines that an increase in electrical load at the output of generator set  110  corresponds to an abrupt load increase if the load increase between the current control cycle and the preceding control cycle exceeds the threshold load value. For example, the threshold load value may be 25-50% of the total capacity of generator set  110 . 
         [0032]    Alternatively or additionally, if the speed in the current cycle is lower than the speed in the proceeding cycle by at least a threshold speed value, controller  106  may determine that an abrupt load increase has occurred at the output of generator set  110  or that the load increase exceeds the predetermined range. According to a further embodiment, the threshold speed value may be set between 0.1% and 0.3% of the rotational speed in the preceding cycle. In other words, controller  106  may determine that an abrupt load increase has occurred if the rotational speed of generator set  110  decreases by a value greater than the threshold speed value. 
         [0033]    Still alternatively or additionally, control system  100  may also check the fuel command to determine if the load increase exceeds the predetermined range. As discussed above, in the normal operating mode, the adjustment of the fuel supply rate by controller  106  is generally continuous or in very small increments. If controller  106  attempts to increase the fuel supply to counter the effects of an abrupt load increase, the fuel command in the current control cycle may include an instruction to increase the fuel supply rate by 1-2% from the previous control cycle. Based on such fuel command from controller  106 , system  100  may determine that an abrupt load increase has occurred at the output of generator set  110  or that the load increase exceeds the predetermined range. 
         [0034]    If control system  100  determines that the load increase sensed at step  202  is within the predetermined range, it may set generator set  110  in the normal operating mode (i.e., the first mode) as discussed above, so that generator set  110  gradually responds to the changes in the electrical load (step  206 ). In the normal operating mode, system  100  may vary the control parameters, such as the fuel supply rate, the output voltage level, and the inlet guide vane angle, in small increments so that generator set  110  gradually adapts to the change in the electrical load. 
         [0035]    If, on the other hand, control system  100  determines that the load increase sensed at step  202  exceeds the predetermined range, it sets generator set  110  in the transient mode, i.e., the second mode (step  208 ). In general, generator set  110  operating in the second mode provides a rate of adjustment of the control parameters greater than the rate of adjustment during the first mode. Specifically, when an abrupt load increase is detected, system  100  may set generator set  110  to the second mode and may determine a step increase for the fuel supply rate. For example, if the electrical load of generator  118  increases by 25-50% of the capacity of generator set  110 , fuel control module  102  may determine that the fuel supply rate must be step increased by 5-15% from the preceding cycle. Alternatively, if the rotational speed of shaft  130  decreases by 0.1-0.3% from the preceding control cycle, fuel control module  102  may also determine that the fuel supply rate must be step increased by 5-15%. Still alternatively, if controller  106  generates a fuel command in the current control cycle to instruct fuel valve  108  to increase the fuel supply rate by 1-2%, fuel control module  102  may then modify the fuel command to include an instruction for an additional 5-15% step increase in the fuel supply rate. 
         [0036]    Additionally or alternatively, control system  100  operating in the second mode may determine a step decrease for the output voltage level in response to the detected abrupt load increase. For example, if the electrical load on output lines  119  increases by 25-50% of the capacity of generator set  110 , voltage control module  103  may determine that the output voltage level must be step decreased by 5-15% to counter the abrupt load increase. Alternatively, if the rotational speed of shaft  130  decreases by 0.1-0.3% from the preceding control cycle, voltage control module  103  may also determine that the output voltage level must be step decreased by 5-15%. Still alternatively, if controller  106  generates a fuel command to instruct fuel valve  108  to increases the fuel supply rate by 1-2%, voltage control module  104  may then determine that the output voltage level must be step decreased by 5-15%. 
         [0037]    Still additionally or alternatively, control system  100  may set the generator set  110  to the second mode and determine a step increase for the inlet guide vane angle in response to the detected abrupt load increase. Specifically, when system  100  detects an abrupt load increase as described above, inlet guide vane module  104  may signal to open the inlet guide vane from the current position to the fully open position within one second. According to a further embodiment, inlet guide vane module  104  may determine a rate for the inlet guide vanes equal to, for example, 50% of a full stroke angle per second. For instance, if the full stroke angle of the inlet guide vanes is 50° from fully closed to fully open, the rate set by inlet guide vane module  104  in response to the abrupt load increase is 25° per second. The full stroke angle of the inlet guide vanes may vary, depending on the configuration of generator set  110 . In addition, inlet guide vane module  104  may set the rate for the inlet guide vanes at other values greater or less than 50% of the full stroke angle per second. In general, the greater the rate, the faster the inlet guide vanes reach the fully open position in response to the abrupt load increase. 
         [0038]    Further at step  208 , fuel control module  102  may generate and transmit fuel control signal  101  to fuel valve  108 , including the instruction for step increasing the fuel supply rate. The step increase in fuel supply rate provides generator set  110  with additional energy to satisfy the abrupt load increase and to maintain the rotational speed of generator set  110 . 
         [0039]    Alternatively, voltage control module  103  may generate and transmit voltage control signal  117  to voltage regulator  121 , including the instruction for step decreasing the output voltage level on lines  119 . The decreased output voltage level effectively reduces the electrical load drawn from generator set  110  and maintains the rotational speed of generator set  110 . 
         [0040]    Still alternatively, inlet guide vane module  104  may generate and transmit inlet guide vane signal  126  to inlet guide vanes  134  and to increase the inlet guide vane angle according to the incremental rate or angle value determined at step  210 . The step increase in the inlet guide vane angle increases incoming air flow  111 , which allows generator set  110  to generate extra power output to satisfy the abrupt load increase. In general, inlet guide vane module  104  instructs the inlet guide vanes to reach the fully open position in less than one second in response to the detection of the abrupt load increase. 
         [0041]    According to a further embodiment, system  100  operating in the second mode may selectively perform one or more of the above adjustments in each control cycle. For example, if electrical equipment  122  is voltage sensitive and requires the output voltage remain at a given level during its operation, system  100  may omit the voltage adjustment, so that the output voltage level may be maintained, while adjusting the fuel supply rate and/or the inlet guide vane angle to satisfy the abrupt load increase. 
         [0042]    Still alternatively, the abrupt load increase caused by electrical equipment  122  may be in the form of discontinuous pulses. As a result, increasing the fuel supply rate may deteriorate system stability. Thus, system  100  may omit the fuel adjustment or limit the increase in the fuel supply rate, while adjusting the voltage output level and/or the inlet guide vane angle in response to the abrupt load increase. Other combinations of the adjustments may also be performed by system  100  as recognized by one skilled in the art. 
         [0043]    According to still another embodiment, the inlet guide vane adjustment may be performed in every control cycle when an abrupt load increase is detected, so that the inlet guide vane angle is set to the fully open position whenever there is an abrupt load increase. 
         [0044]    Here, the terms “step increase” and “step decrease” each refer to an instantaneous transition or change. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed systems. Others embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed systems. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.