Electric motor for fuel pump with improved shutdown features

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A prior art electric motor control20is illustrated inFIG. 1. As shown, a pair of redundant stators22and24are provided to drive a shaft26. The stators include three coils associated with three phases of electrical power, and control coils27.

The buck regulator comprises of a power stage32, a controller30and inductor27. The buck inductor27utilizes a control coil of a regulated permanent magnet machine. The buck regulators control the DC bus current to the inverters28. In this prior art system, a signal to shut down one of the faulty electric motors22or24would come from34, 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. 2is a schematic of an improved system39. In system39, a prime mover40such as a gas turbine engine, is driven to rotate and generates power by an electric power generating system42. As known, the power generating system42supplies power over a DC bus43to customer load44. The customer load44may be any number of components on an aircraft. In addition, an accessory bus45supplies power to a motor controller46, which controls a fuel pump48. In this basic architecture, the bus45may 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 switch50supplies a shutdown signal to the motor controller46. When a shutdown signal is received at the motor controller46, a signal52is sent back to the electric power generating system42.

FIG. 3shows the motor controller46. As shown, the fuel pump48is provided with a rotor55. The plurality of stator windings54receive voltage through an inverter56. A DC power source58, which, in a disclosed embodiment, is the accessory bus45, supplies the power through the inverter56to control the current associated with the three phase coils54, to in turn drive the rotor55. A control coil60is also associated with the stator for the electric motor. A coil control switch62, which may be a MOSFET, receives a shutdown signal such as shown at68. A pulse width modulator66receives the shutdown signal from68, and sends a signal through a gate drive64to control the switch62. When the switch62is opened, then power no longer flows to the control coil60, and the motor is no longer driven. In the dual redundant arrangement the control coil60would electromagnetically decouple this motor from the second one sharing the same rotor shaft. The signal at68may 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 theFIG. 3schematic, the switch62, which functions as a shut off switch, is positioned intermediate the inverter56and the control coil60, and upstream of the control coil60, and downstream of the inverter56, relative to power flow.

The motor control utilizes a current-mode bidirectional voltage source inverter56. A position feedback signal70is sent to a speed detector72, a coordinate transformation unit202and a space vector modulator88. The coordinate transformation unit202derives direct (Id_fdbk) and quadrature (Iq-fdbk) components of stator current from current transducers201. A comparator74, which also receives a reference speed signal (spd_ref), produces a speed error signal that is processed by a proportional-integral regulator (PI)76to obtain torque producing reference (Iq_ref). A shutdown signal78is provided on this line, and may be driven to open when the signal is provided at68. At this point, the desired current Iq_ref would become zero at the comparator80. A look-up table84produces a direct current reference (Id-ref) as a function of speed. The motor's d and q current loops are closed using comparators86and80, and PI regulators203and204respectively. The outputs of the current loop PI regulators (Vd_ref and Vq_ref) would then go to a space vector modulator88, which would in turn control the gate drives90to control current in the stator windings54.

In addition, when there is a zero signal such as a shutdown signal from the switch78, a differentiator82supplies a feed forward signal52back to a voltage regulator for the power generating system. This will be explained with regard toFIG. 4.

An electric power generating system42is shown inFIG. 4. The prime mover40, which may be a gas turbine engine, is associated with a generator213. Generator213can be a flux regulated permanent magnet machine with control coil92. Generator213supplies power through a rectifier43, DC filter is comprised of a capacitor206, and to a DC bus43, and the accessory bus45. Power quality/EMI filter212is used to ensure that power quality provided to the customer load meets specification requirements.

The voltage regulation on DC bus43is achieved by controlling current in the control winding92in response to the feedback voltage (Vdc_fdbk) obtained from the voltage transducer207, and includes voltage and current loops. The voltage loop includes a comparator102and a PI regulator211. The comparator102derives a voltage error between reference (Vdc_ref) and a feedback signal (Vdc_fdbk). In addition, the comparator102includes a third input to accommodate a feedforward signal from the motor-pump controller48to maintain power quality on DC bus during large transients associated with the motor-pump, such as fast shutdown. The PI regulator211produces a current reference signal (Icc_ref) in response to the output of comparator102.

The current loop includes an H-bridge94, a current transducer214, a comparator100, a PI regulator209, a PWM modulator210, and a gate drive96A comparator100derives a current error signal between current reference (Icc_ref) and feedback signal (Icc_ref) obtained form the current transducer208. This signal is processed by a PI regulator209to derive a duty cycle for the PWM modulator210that controls the gate drive96. The H-bridge94controls current in the control coil92in 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 bus43. However, by providing the feedforward signal52back upstream, the voltage transients on the DC bus43can 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.