Abstract:
An electric motor for a fuel pump is provided with a shutdown switch positioned intermediate an inverter, and its control coil. In this location, the shutdown function can be achieved without heavy components. In another feature, when the fuel pump is shut down, a signal is sent upstream to a voltage regulator associated with a generator, such that the voltage supplied downstream by the generator can be reduced to eliminate any potential voltage spike due to the shutdown of the electric motor. The electric motor with shutdown switch enables low weight fault tolerant flux regulated machines.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to a control for a fuel pump, wherein the fuel pump motor can be stopped quickly with simple controls. 
     Electric motor controls are becoming more and more complex. Typically, three phases of power are supplied to a stator to drive a rotor for the electric motor. In addition, a control coil controls the operation of the motor. An inverter is provided with a gate drive, and controls the flow of the power to coils associated with the three phases. 
     It is known to have a buck regulator upstream of the inverter, and acting to control the voltage supply from a voltage source to the inverter. 
     In many applications, it becomes necessary to stop the flow of fuel under certain emergency conditions. As an example, if the motor experiences high current spikes, voltage spikes, etc., it is desirable to stop the operation of the electric motor immediately. Further, other conditions, such as a fire, fuel leakage, etc., would point to immediately stopping the electric motor. Thus, it is desirable to stop a fuel pump within a matter of milliseconds once a decision is made to stop the fuel pump. 
     Fuel pumps of the above sort become particularly challenging to control when mounted to provide fuel to a gas turbine engine on an aircraft. In such applications, the size and weight of the control become critical. It always desirable to decrease the weight of components associated with aircraft engines. 
     In the prior art, the shut off signal for the electric motor flowed through the buck regulator. Since, the power flow in the prior art is unidirectional, a transient suppressor device on a dc bus would be required to maintain voltage within specification limits during fast shutdown, when the motor operates in the regenerative mode. In addition, the prior art utilizes control winding not only as a protective device in the dual redundancy arrangement, but as a buck regulator inductor. This required that the size and weight of the control be larger than would be desirable. 
     SUMMARY OF THE INVENTION 
     In the disclosed embodiment of this invention, a shut off switch for an electric motor to drive a fuel pump is positioned to open a circuit adjacent to a control coil, and downstream of a motor control inverter. Thus, the control is relatively lightweight. In a separate feature, when it is determined that the drive motor for the fuel pump has been entered a regeneration mode for a fast shutdown, a signal is sent back upstream to a control for an associated generator, to reduce the current supplied by the generator to account for an expected voltage spike now that the fuel pump electric motor has been entered a regeneration mode. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior art motor control. 
         FIG. 2  is a schematic of an overall system incorporating in the present invention. 
         FIG. 3  is a schematic for a fuel pump motor control. 
         FIG. 4  is a more detailed schematic of the  FIG. 3  system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A prior art electric motor control  20  is illustrated in  FIG. 1 . As shown, a pair of redundant stators  22  and  24  are provided to drive a shaft  26 . The stators include three coils associated with three phases of electrical power, and control coils  27 . 
     The buck regulator comprises of a power stage  32 , a controller  30  and inductor  27 . The buck inductor  27  utilizes a control coil of a regulated permanent magnet machine. The buck regulators control the DC bus current to the inverters  28 . In this prior art system, a signal to shut down one of the faulty electric motors  22  or  24  would come from  34 , into the buck regulators. This is undesirable, since the control coil is sized to handle full motor power to achieve full torque control and not just for protection. The electromagnetic decoupling in dual redundant arrangement can be achieved by designing the motor with considerably smaller size control winding. The prior art does not includes a transient suppressor (a power resistor connected via power switch to the DC bus) that would be required during fuel pump fast shutdown to keep DC bus voltage within specification limits, when the motor operates in a regenerative mode. This resulted in undesirably heavy components required by the control for the aircraft fuel pump. 
       FIG. 2  is a schematic of an improved system  39 . In system  39 , a prime mover  40  such as a gas turbine engine, is driven to rotate and generates power by an electric power generating system  42 . As known, the power generating system  42  supplies power over a DC bus  43  to customer load  44 . The customer load  44  may be any number of components on an aircraft. In addition, an accessory bus  45  supplies power to a motor controller  46 , which controls a fuel pump  48 . In this basic architecture, the bus  45  may also supply power to a plurality of accessories which are associated with the gas turbine engine, such as a water pump, a fuel pump, and a lubricant pump. 
     A shutdown switch  50  supplies a shutdown signal to the motor controller  46 . When a shutdown signal is received at the motor controller  46 , a signal  52  is sent back to the electric power generating system  42 . 
       FIG. 3  shows the motor controller  46 . As shown, the fuel pump  48  is provided with a rotor  55 . The plurality of stator windings  54  receive voltage through an inverter  56 . A DC power source  58 , which, in a disclosed embodiment, is the accessory bus  45 , supplies the power through the inverter  56  to control the current associated with the three phase coils  54 , to in turn drive the rotor  55 . A control coil  60  is also associated with the stator for the electric motor. A coil control switch  62 , which may be a MOSFET, receives a shutdown signal such as shown at  68 . A pulse width modulator  66  receives the shutdown signal from  68 , and sends a signal through a gate drive  64  to control the switch  62 . When the switch  62  is opened, then power no longer flows to the control coil  60 , and the motor is no longer driven. In the dual redundant arrangement the control coil  60  would electromagnetically decouple this motor from the second one sharing the same rotor shaft. The signal at  68  may be a signal of a potential problem, such as an over-current, an over-voltage, or some other type of emergency such as a fire or fuel leak. As is clear from the  FIG. 3  schematic, the switch  62 , which functions as a shut off switch, is positioned intermediate the inverter  56  and the control coil  60 , and upstream of the control coil  60 , and downstream of the inverter  56 , relative to power flow. 
     The motor control utilizes a current-mode bidirectional voltage source inverter  56 . A position feedback signal  70  is sent to a speed detector  72 , a coordinate transformation unit  202  and a space vector modulator  88 . The coordinate transformation unit  202  derives direct (Id_fdbk) and quadrature (Iq-fdbk) components of stator current from current transducers  201 . A comparator  74 , which also receives a reference speed signal (spd_ref), produces a speed error signal that is processed by a proportional-integral regulator (PI)  76  to obtain torque producing reference (Iq_ref). A shutdown signal  78  is provided on this line, and may be driven to open when the signal is provided at  68 . At this point, the desired current Iq_ref would become zero at the comparator  80 . A look-up table  84  produces a direct current reference (Id-ref) as a function of speed. The motor&#39;s d and q current loops are closed using comparators  86  and  80 , and PI regulators  203  and  204  respectively. The outputs of the current loop PI regulators (Vd_ref and Vq_ref) would then go to a space vector modulator  88 , which would in turn control the gate drives  90  to control current in the stator windings  54 . 
     In addition, when there is a zero signal such as a shutdown signal from the switch  78 , a differentiator  82  supplies a feed forward signal  52  back to a voltage regulator for the power generating system. This will be explained with regard to  FIG. 4 . 
     An electric power generating system  42  is shown in  FIG. 4 . The prime mover  40 , which may be a gas turbine engine, is associated with a generator  213 . Generator  213  can be a flux regulated permanent magnet machine with control coil  92 . Generator  213  supplies power through a rectifier  43 , DC filter is comprised of a capacitor  206 , and to a DC bus  43 , and the accessory bus  45 . Power quality/EMI filter  212  is used to ensure that power quality provided to the customer load meets specification requirements. 
     The voltage regulation on DC bus  43  is achieved by controlling current in the control winding  92  in response to the feedback voltage (Vdc_fdbk) obtained from the voltage transducer  207 , and includes voltage and current loops. The voltage loop includes a comparator  102  and a PI regulator  211 . The comparator  102  derives a voltage error between reference (Vdc_ref) and a feedback signal (Vdc_fdbk). In addition, the comparator  102  includes a third input to accommodate a feedforward signal from the motor-pump controller  48  to maintain power quality on DC bus during large transients associated with the motor-pump, such as fast shutdown. The PI regulator  211  produces a current reference signal (Icc_ref) in response to the output of comparator  102 . 
     The current loop includes an H-bridge  94 , a current transducer  214 , a comparator  100 , a PI regulator  209 , a PWM modulator  210 , and a gate drive  96 A comparator  100  derives a current error signal between current reference (Icc_ref) and feedback signal (Icc_ref) obtained form the current transducer  208 . This signal is processed by a PI regulator  209  to derive a duty cycle for the PWM modulator  210  that controls the gate drive  96 . The H-bridge  94  controls current in the control coil  92  in response to the current reference Icc_ref. 
     When the fuel pump electric motor is set into regenerative mode to achieve fast shutdown, there could be a spike of voltage supplied downstream through the bus  43 . However, by providing the feedforward signal  52  back upstream, the voltage transients on the DC bus  43  can be significantly improved. 
     In sum, the present invention provides lower weight system to achieve fast shutdown and a fault redundant architecture of an electric motor for a fuel pump. The invention is particularly well suited for use in controlling a fuel pump for a gas turbine engine in an aircraft application. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.