Abstract:
Properly managing surges of regenerative power is needed in systems where power is generated and distributed to mechanical and electrical loads to protect them from overvoltage. A controller provides protection against excess regenerative power when these systems operate at a wide range of speeds. Controller functions and control methods for overvoltage protection may include an added control loop for detecting an overvoltage condition, calculating a power factor and generating a gating signal to transition the controller into a motoring mode that converts the excess regenerative power into mechanical power.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to apparatus, methods and system configuration for protecting power generation, distribution and management systems against overvoltage in a broad range of machine conditions. More specifically, the present invention relates to apparatus, methods and system configuration for protecting a More Electric Aircraft against transient overvoltage when the system is utilized at less than 100% rated speed. 
         [0002]    Power systems such as a More Electric Aircraft and electric vehicles can be susceptible to excessive power regeneration during braking of the motors or actuators that can cause overvoltage. Resistors are often used in these systems to convert excess electrical energy which is dissipated in the form of heat. However, these resistors are heavy and bulky and add to the weight of the system. 
         [0003]    In an effort to address the above potential problem of overvoltage, an experimental system in which power is generated and distributed to mechanical and electrical loads, such as in an aircraft, was set up to simulate control configurations capable of managing an overvoltage event in such a manner as to dissipate the excess power in the form of mechanical energy. A controller configuration initially tested in an effort to manage transient overvoltage events appeared to work well at near 100% of machine rated speed, but failed to control overvoltage at 70% of the machine rated speed. 
         [0004]    As can be seen, there is a need for a better system to deal with the power regeneration surges originating, for example, from peak use of motors and actuators. 
       SUMMARY OF THE INVENTION 
       [0005]    In one aspect of the present invention, a controller comprises a first regulator programmed to compute a power factor from a dc bus voltage signal fed to the first regulator; and a second regulator programmed to compute an ac current magnitude from the power factor and from a dc load current signal fed into the second regulator. 
         [0006]    In another aspect of the present invention, a method for regulating a power generation, distribution and management system comprises feeding a dc bus voltage signal to the controller; feeding a dc load current signal; computing a power factor from the dc bus voltage input signal; computing an ac current magnitude from the power factor and the dc load current signal; computing ac current command values in a synchronous frame from the power factor and from the ac current magnitude; computing differences between the ac current command values and measured ac current values in the synchronous frame; computing output voltage command values from the computed differences; and producing gating signals from the output voltage command values. 
         [0007]    In yet another aspect of the present invention, a power generation, distribution and management system comprises at least a mechanical power generator; at least one motor; at least one mechanical load; a plurality of electrical loads containing a plurality of bus capacitors; and a controller in direct communication with the motor, the electrical loads and the bus capacitors. 
         [0008]    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 
         [0009]      FIG. 1  is a schematic diagram of a power generation, distribution and management system having a controller according to an embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic diagram of the controller of  FIG. 1  for a power generation, distribution and management system according to an embodiment of the present invention; 
           [0011]      FIG. 3  is a schematic diagram of a modified controller of  FIG. 1  according to an embodiment of the present invention; 
           [0012]      FIG. 4  is a schematic diagram of a modified current magnitude regulator of the controller of  FIG. 3  according to an embodiment of the present invention; 
           [0013]      FIG. 5  is a schematic diagram of a modified power factor control regulator of the controller of  FIG. 3  according to an embodiment of the present invention; 
           [0014]      FIG. 6  is a block schematic of a Power and Thermal Management System used in the Examples to simulate the control system of the present invention; 
           [0015]      FIG. 7  is a flow chart showing a method according to the present invention; 
           [0016]      FIG. 8  is a response chart to the simulation of a control method for a system operating at 100% of the rated speed; 
           [0017]      FIG. 9  is a response chart to the simulation of a control method for a system operating at 70% of the rated speed; 
           [0018]      FIG. 10  is a response chart to the simulation of a control method according to an embodiment of the present invention for a system operating at 100% of the rated speed; and 
           [0019]      FIG. 11  is a response chart to the simulation of a control method according to an embodiment of the present invention for a system operating at 70% of the rated speed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The following detailed description is of the best currently contemplated modes of carrying out 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. 
         [0021]    Various inventive features are described below that can be each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems above may not be fully addressed by any of the features described below. 
         [0022]    The present invention generally provides a system configuration, a controller and controller functions, and a method for regulating the power regeneration in a power generation, distribution and management system such as a More Electric Aircraft (MEA) or an electric vehicle. A power generation, distribution and management system may include a prime power source, a machine containing a motor, a controller, mechanical loads and electrical loads. The prime power source moves the motor which produces a three phase alternate current system output. The controller rectifies and regulates the electrical output, typically to a 270 direct current Volts, which provides power to the electrical loads. During normal operations, the prime power source drives the machine motor and the mechanical loads and provides power to the electrical loads. Thus: 
         [0000]      Prime Power source=Motor power+Mechanical loads+Electrical loads. 
         [0000]    In an aircraft, for example, a turbo generator moves the aircraft engine which produces an alternate current (ac current) through the controller. 
         [0023]    In a power generating operation, the controller converts the alternate current into a regulated direct current output by adjusting the power factor and the alternate current magnitude. The direct current (dc current) output supplies the electromechanical loads whose components include valves, compressors and the cooling system, and the electrical load components including for example the lights, the main engine starter, the radar, the actuators and the avionics. 
         [0024]    The system of the present invention may be configured to convert electrical energy into mechanical energy for use by the mechanical loads. This is unlike the prior art of using resistors to convert excess electrical energy into heat. The controller configuration of the present invention may provide control loops to calculate a power factor from which a gating signal is generated in a feed forward path. If regenerative energy is returned to the controller from the loads and charges the direct current bus capacitor and the bus capacitance voltage exceeds the threshold, the controller will transition into motoring mode by adjusting its power factor. As such, the energy from the direct current bus will be converted into mechanical power that is directed to drive a mechanical load. Under these conditions, both the motor and prime power source provide mechanical power to the loads as follows: 
         [0000]      Prime Power source+Motor power=Mechanical loads+Electrical loads. 
         [0025]    Referring to  FIG. 1 , there is shown a generalized diagram of a power generation, distribution and management system including a prime power source  73 , a machine containing a motor  76 , a controller  77 , mechanical loads  71 , and electrical loads  79 . The prime power source  73  may move the motor  76  which may produce a three phase alternate current system output  75 . The controller  77  may rectify and regulate the electrical output typically to 270 direct current Volts which may provide power to the electrical loads  79  and may charge bus capacitors contained within the electrical loads. During normal operations, the prime power source may drive the machine motor and the mechanical loads and provide power to the mechanical loads and to the electrical loads. 
         [0026]    Referring to  FIG. 2 , there is shown a block diagram of a controller  10 , which may regulate the dc bus voltage (Vdc) by adjusting the power factor and the command ac current magnitude. The dc bus voltage may be compared with a voltage set point and processed by regulator PI_Reg_ 1   51  which is a proportional integral loop programmed to calculate a power factor (pf). Controller  10  is one embodiment of controller  77  of  FIG. 1 . The ac current magnitude (Imag) may be processed by the ac current magnitude regulator Fn_ 1   55 , which is a pre-defined function that computes the ac current magnitude (Imag) from the dc bus or load current (Idc). The resulting ac current magnitude (Imag) and power factor (pf) may be used in computing the command ac currents by the current command regulator  56  in a synchronous frame (Id* and Iq*). The difference between the current commands (Id* and Iq*) and measured currents (Id and Iq) may be processed with voltage control regulators PI_Reg_ 2   52  and PI_Reg_ 3   54  to produce output voltage commands (Vd and Vq). Id and Iq are measured at a point between the motor and the controller in the system. The difference between the current commands (Id* and Iq*) and measured currents (Id and Iq) may be calculated by an ac current subtraction function  57 . The gating signal generator  53  may produce the gating signal to the controller in accordance with control commands (Vd and Vq). During the regenerative operation, the load can retrofit power to the dc bus and charge the bus capacitor. If the regenerative power is in excess the power required to charge the bus capacitors, the controller may change the power factor such that the controller switches to operating in a motoring mode which converts the regenerative electrical power into mechanical power by the mechanical loads. 
         [0027]    Referring to  FIG. 3 , there is shown a block diagram of a modified controller  20  according to an embodiment of the present invention. Controller  20  is another embodiment of controller  77  of  FIG. 1 . In this configuration, ac current magnitude regulator Fn_ 1   55  and power factor control regulator PI_Reg_ 1   51  may be modified into regulators Fn_ 1   x    55 A and PI_Reg_ 1   x    51 A respectively. In the modified controller configuration  20 , the modified power factor control regulator PI_Reg_ 1   x    51 A may process the dc bus voltage signal, Vdc, and a voltage error signal, Verr, and may compute a power factor. The voltage error signal, Verr, may be calculated from the difference between the dc bus voltage, Vdc, and a predetermined voltage set-point. The difference calculation may be performed by a dc voltage subtraction function  58 . The modified ac current magnitude regulator Fn_ 1   x    55 A may process the calculated power factor and the dc load current (Idc) and calculate the ac current magnitude (Imag). The remaining functions and regulator blocks for the modified controller configuration  20  may be the same as those of controller configuration  10  of  FIG. 2 . 
         [0028]    Referring to  FIG. 4 , there is shown a configuration of the modified power factor regulator  30 , also represented by PI_Reg_ 1   x    51 A. The control function of control regulator block Fn_ 1   55  may be that of controller configuration  10 , but processed with the additional control path using power factor pf. In accordance with this control path, the dc bus current (Idc) may be processed by an ac current magnitude regulator Fn_ 1   55  to produce the command ac current magnitude (Imag_ 1 ). In addition, the power factor (pf) may be converted to an absolute value by multiplier function  59  and multiplied by constant K 1  at multiplier function  11 . The product of this results may be multiplied by a constant −K at multiplier function  13  and by the dc input load current (Idc) at multiplier function  18  to yield a modified power factor (pfx). The constant (−K) is the inverse in polarity of the load input current Idc. The modified power factor may be processed through an ac current magnitude regulator Fn_ 1   55  to yield command ac current magnitude Imag_ 2 . This path may give a positive value of command ac current magnitude, (Imag_ 2 ), and modulate the command ac current magnitude, Imag, in accordance with the regenerative power. A selector function, HighWin,  12  may select the greater value between command ac current magnitude Imag_ 1  and command ac current magnitude Imag_ 2  and set it as Imag. Therefore, the command ac current magnitude Imag_ 1  may be selected at normal operation, but Imag_ 2  may be used during the regenerative power condition. Accordingly, the ac current magnitude adjustment may operate in a feedforward path. 
         [0029]    Referring to  FIG. 5 , there is shown a modified power factor control regulator diagram  40  i.e., control regulator PI_Reg_ 1   x    51 A. This regulator may be a modified configuration of the power control regulator PI_Reg_ 1   51  used in controller configuration  10 . PI_Reg_ 1   x    51 A comprises of two sections: an operational control section and a regenerative power control section. The operational control section may compute the power factor from the voltage differences (Verr) between the measured dc bus voltage (Vdc) and a voltage set point. The voltage difference (Verr) computation may be performed by regulator function PI_Reg_ 1   51  used in the operational method and produces the power factor Pf_ 1 . The regenerative path includes the dc bus voltage measurement (Vdc), gain function Kg  15 , power factor selector function HighWin  16 , a limiter function  48  and integrator regulator function PI_Reg_ 2   70 . In this path, a threshold voltage value (OV_Threshold) may be subtracted from the measured voltage Vdc using a dc bus voltage subtraction function  17 , and the result may be multiplied by a gain function Kg  15  to yield Pf_ 3 . The subtraction result may be processed by integrator regulator function PI_Reg_ 2   70  along with an initializing value. The integrator regulator function  70  produces power factor Pf_ 4 . Power factor selector function, HighWin  16  may select the greater of power factors Pf_ 3  and Pf_ 4 , and the result may be fed into a limiter function  48  that may limit the output to between 0 and 1. The output value of the limiter may be set as power factor Pf_ 2 , which may be added to power factor Pf_ 1  to yield the power factor for the regulator, pf. Pf_ 2  may be fed back into the integrator regulator function  70  to replace the initializing value. The regenerative path may only be active when the regenerative power is detected and the bus voltage exceeds the threshold (Ov_Threshold). Under these conditions, the regenerative power control section may modify the power factor when the bus voltage (Vdc) exceeds the voltage threshold (e.g., 290 V). Accordingly, the regeneration section may operate in a feedforward path. If the voltage difference Verr is zero or negative, Pf_ 2  may be zero and the power factor pf may be generated by the operational section. 
         [0030]    Referring to  FIG. 6 , there is shown a diagram of a Power and Thermal Management (PTM) System used in simulation experiments to test the controller according to the present invention. This system, designed to simulate aircraft systems, includes an Environmental Control Sub-system (ECS) including a compressor  81  and a turbo machine  83 , and an Electrical Power System (EPS). Both the ECS and EPS are connected to the same shaft. The EPS includes a Permanent Magnet Machine (PMM)  85  and a controller  87 . The ECS controls the compressor  81  and turbo machine  83  and may provide thermal management for the aircraft loads  89 . The controller may convert the ac input into a regulated 270 Vdc output. The simulations may be carried out under regenerative power conditions, where the peak power is the rated power of the PTM System, and the machine  83  may operate at between about 70% to about 100% of the rated speed. The PMM  85  controller may adjust the power factor and ac current magnitude to operate in a motoring mode. In this mode, energy returned from the load may be converted into mechanical energy and used by the ECS. 
         [0031]    Referring to  FIG. 7 , there is shown a flow chart depicting a method ( 60 ) according to the present invention. Step  62  may include computing a power factor from a direct bus input signal. Step  64  may include computing an ac current magnitude from the power factor and a dc load current input signal. Step  66  may include computing ac current command values in a synchronous frame from the power factor and from the ac current magnitude. Step  67  may include computing differences between the ac current command values and current system values that are measured between the motor and the controller in a synchronous frame. Step  68  may include computing output voltage command values from the differences between the ac current command values and current system values that are measured between the motor and the controller. Step  69  may include producing signals from the output voltage command values. The gating signals may transition the system into a motoring mode from a regenerative mode if excess regeneration power is detected in order to convert the excess regenerative power into mechanical energy. 
       EXAMPLES 
       [0032]    The simulation of the control methods described in this application was conducted using a Power and Thermal Management (PTM) System shown in  FIG. 6 . 
       Example 1 
       [0033]    Referring to  FIG. 8 , a chart of the dc bus voltage (Vdc), % power, and % load dc current plotted vs. time in msec is shown representing a simulation for controller configuration  10  described in  FIG. 2  operating at 100% of the rated speed. The regenerative power is retrofitted back to the dc bus and the energy is converted into mechanical power for the Environmental Control System (ECS). The maximum voltage at the bus is about 325 Vdc when the peak power is returned to the bus. 
       Example 2 
       [0034]    Referring to  FIG. 9 , a chart of the dc bus voltage (Vdc), % power, and % load dc current plotted vs. time in msec is shown representing a simulation for controller configuration  10  described in  FIG. 2  operating at 70% of the rated speed. The back emf of the PMM is reduced at this lower speed. As such, the output power capability of the PMM is also reduced. The regenerative power is retrofitted back to the dc bus at around 5 milliseconds and 10 milliseconds. The peak voltage rose to 350 Vdc at 5.5 milliseconds and 600 Vdc at 115 milliseconds. During the first event, the command ac current magnitude, Imag, was assumed at the maximum magnitude due to the initial start up transient. Therefore, the PMM system was capable of maintaining the peak voltage at 350 Vdc. In the second incident, the current command was reduced and the controller malfunctioned. This controller configuration failed to regulate the output voltage which surged to 600 Vdc. 
       Example 3 
       [0035]    Referring to  FIG. 10 , a chart of the dc bus voltage (Vdc), % power, and % load dc current plotted vs. time in msec is shown representing a simulation for the controller configuration  20  described in  FIG. 3  operating at 100% of the rated speed. When the voltage exceeds 300 Vdc, the angle compensation control loop is activated and converts the electrical power into mechanical power for the ECS. The maximum voltage at the bus is about 310 Vdc, which is about 15 Vdc lower than the voltage generated by controller configuration  10  in Example 1. 
       Example 4 
       [0036]    Referring to  FIG. 11 , a chart of the dc bus voltage (Vdc), % power, and % load dc current plotted vs. time in msec is shown representing a simulation for the controller configuration  20  described in  FIG. 3  operating at 70% of the rated speed. The back emf of the PMM was reduced proportionally and the output power capability of the PMM was reduced accordingly. During the regenerative operation, both angle compensation control loop and current magnitude control loop were activated. When the dc bus voltage exceeded 300 Vdc, the angle compensation modified the power factor of the controller and operated in the motoring mode. Electrical power was converted into mechanical power. Also, the current magnitude mode increased in order to meet the regenerative power transient. The simulation results showed that the transient peak voltage was consistent at about 317 Vdc. This controller configuration appears to provide more stable and consistent performance compared with controller configuration  10  of Example 2. 
         [0037]    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.