Patent Description:
Typically, an electric motor is used to spin a main turbine shaft of an engine (e.g., an aircraft engine) until there is enough air airflow through the compressor and combustion chamber to light the engine and spin the engine up to its operating speed. Starting an engine via an electric motor is typically governed by a master solenoid, which supplies electrical power through an inverter which is comprised of a plurality of switches. When the motor commanded to turn off, e.g., by closing one or more of the plurality of switches, the motor will continue to rotate because due inertia where the motor will act as a generator and thus pump back electrical energy to a DC bus which can increase voltage to on the bus to dangerously high values. To prevent this, a brake resistor circuit works by monitoring the DC bus voltage and activating the brake resistor circuit if it senses the DC link voltage above a set voltage, to absorb the excess voltage until the DC bus voltage drops below a safe voltage limit. Starter circuits are disclosed in <CIT>, <CIT> and <CIT>.

Solenoid - driven electromechanical switches with self - testing functionality are disclosed in <CIT> and in <CIT>.

Typically, the solenoid and braking circuits each have two high side and two low switches connecting the solenoid coil and brake resistor respectively. In this set up, the solenoid and braking circuits will become functional when both switches are in the on state and current flows through an inductor coil of the solenoid or the brake resistors. But this also leads to an unnecessary duplication of common circuits which increases the number of circuit components as well as area occupied by the circuits on a circuit board. Therefore, there remains a need in the art for improvements to engine starter circuits in the aerospace industry. This disclosure provides a solution for this need.

In accordance with the invention, a system is provided as defined by claim <NUM>.

In embodiments, the solenoid circuit further can include an inductor coil configured to provide current to the electric machine, a freewheeling diode configured to provide a path for decay of current through the inductor coil, and a solenoid switch driven by a respective switch drive, configured to control electrical communication from the inductor coil to the electric machine. In embodiments, the braking circuit can include a brake resistor configured to provide a resistance to current generated by the electric machine flowing towards the electrical bus, a freewheeling diode configured to provide a path for decay of current through the brake resistor; and a brake switch driven by a respective switch drive, configured to control electrical communication from the electric machine to ground through the brake resistor and to prevent electrical communication from the electric machine to the electrical bus.

In embodiments, the common switch, the solenoid switch, and the brake switch each can include an insulated-gate bipolar transistor.

The system includes an inverter, configured to invert a direct current supplied by the electrical bus into an alternating three phase current to be used by the electric machine. In embodiments, a power of breaking can be disposed between the inverter and the electric machine, configured to hold the electric machine <NUM> in a stand still mode when no power is applied to the electric machine.

A starter built-in-test (BIT) circuit is included in the system. The starter BIT circuit can include a current sense resistor disposed between the common switch and each of the solenoid circuit and the braking circuit configured to sense a current flowing through the starter circuit to determine a state of the common switch and output a signal indicative of the state of the common switch to a controller.

The solenoid BIT circuit can include a current sense resistor disposed between the inductor coil and the solenoid switch configured to sense a current flowing through the solenoid circuit to determine a state of the solenoid switch and output a signal indicative of the state of the solenoid switch to a controller. In embodiments, the braking BIT circuit can include a current sense resistor disposed between the brake resistor and the braking switch configured to sense a current flowing through the braking circuit to determine a state of the brake switch and output a signal indicative of the state of the brake switch to a controller.

In embodiments, the system includes the controller and the controller can be configured to compare each of the signal indicative of the state of the common switch, the signal indicative of the state of the solenoid switch, and the signal indicative of the state of the brake switch to a respective reference state for the common switch, the solenoid switch, and the brake switch to determine if a fault has occurred in any of the starter circuit, the solenoid circuit, and/or the brake circuit.

In embodiments, the load can include an engine, and the system can further include the engine. The electric machine can be mechanically coupled to a turbine shaft of the engine to drive the engine (e.g., to start the engine). In certain embodiments, the engine can include an aircraft engine.

In accordance with the invention, a method is provided as defined by claim <NUM>.

The method can include, in a starter mode, maintaining the common switch in an on state, energizing an inductor coil, and placing a solenoid switch in an on state to connect an inverter to the electric machine to power the electric machine.

The method can include, in a braking mode, placing the solenoid switch in an off state to denergize the inductor coil, placing a freewheeling diode in an on state to provide a path for decay of current through a inductor coil. In the braking mode, the method can also include monitoring a voltage of the electrical bus, placing a brake switch in an on state when the voltage of the electrical bus exceeds a predetermined voltage threshold to connect a brake resistor of the braking circuit to ground, continuing monitoring the voltage of the electrical bus, and placing the brake switch in an off state when the voltage of the electrical bus is below the predetermined voltage threshold. In embodiments, the method can include, in an idle mode, placing the common switch, the solenoid switch, and the braking switch in an off state to prevent any current from being supplied from the electrical bus to the electric machine.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, an illustrative view of an embodiment of a system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments and/or aspects of this disclosure are shown in <FIG>.

In accordance with at least one aspect of this disclosure, an engine <NUM> (e.g., an aircraft turbine engine) can include a turbine <NUM> mounted to a turbine shaft <NUM> to rotate the turbine <NUM>. A starter system <NUM> can include a starter circuit <NUM>, for example for powering the starter system <NUM> to start the engine <NUM>. More specifically, the starter circuit <NUM> is configured to provide power to an electric machine <NUM> (e.g., an electric motor capable of also acting as a generator) coupled to the turbine shaft <NUM> to drive the engine <NUM>.

Referring now to <FIG>, the starter circuit <NUM> includes a voltage input <NUM> provided to the starter circuit via an electrical bus <NUM>, a solenoid circuit <NUM> configured to provide power to the electric machine <NUM>, and a braking circuit <NUM> configured to prevent power generated by the electric machine <NUM> from reaching the electrical bus <NUM>. As shown, the solenoid circuit <NUM> and the braking circuit <NUM> are electrically connected the voltage input <NUM> via a common switch <NUM> configured to control electrical communication from the electrical bus <NUM> to the solenoid circuit <NUM> and the braking circuit <NUM>.

The solenoid circuit <NUM> can include an inductor coil <NUM> configured to provide current to the electric machine <NUM>, a freewheeling diode <NUM> configured to provide a path for decay of current through the inductor coil <NUM>, and a solenoid switch <NUM> configured to control electrical communication from the inductor coil <NUM> to the electric machine <NUM>. The braking circuit <NUM> can include a brake resistor <NUM> configured to provide a resistance to current generated by the electric machine <NUM> flowing towards the electrical bus <NUM>, a freewheeling diode <NUM> configured to provide a path for decay of current through the brake resistor <NUM>, and a brake switch <NUM> configured to control electrical communication from the electric machine <NUM> to ground through the brake resistor <NUM> and to prevent electrical communication from the electric machine <NUM> to the electrical bus <NUM>. The common switch <NUM>, the solenoid switch <NUM>, and the brake switch <NUM> can each include a respective insulated-gate bipolar transistor (IGBT) (e.g., as shown), driven by a respective gate drive <NUM>, <NUM>, <NUM> controlled by a controller <NUM>.

An inverter <NUM> is disposed electrically between the starter circuit <NUM> and the electric machine <NUM> to invert a direct current supplied by the electrical bus <NUM> into an alternating three phase current to be used by the electric machine <NUM>. A power of breaking <NUM> can be disposed between the inverter <NUM> and the electric machine <NUM>, configured to hold the electric machine <NUM> in a "stand still" mode when no power is applied to the electric machine <NUM>. The power of breaking <NUM> is operative when the electric machine <NUM> is not moving and receives its power from inverter <NUM>. Said differently, the power of breaking <NUM> can be complementary to the solenoid drive operation.

Each of the starter circuit <NUM>, the solenoid circuit <NUM>, and the braking circuit <NUM> includes respective built-in-test (BIT) circuits. The starter BIT circuit can include a current sense resistor <NUM> disposed between the common switch <NUM> and each of the solenoid circuit <NUM> and the braking circuit <NUM> configured to sense a current flowing through the starter circuit <NUM> to determine a state of the common switch <NUM> and output a signal indicative of the state of the common switch <NUM> to the controller <NUM>.

Similarly, the solenoid BIT circuit, can include a current sense resistor <NUM> disposed between the inductor coil <NUM> and the solenoid switch <NUM> configured to sense a current flowing through the solenoid circuit <NUM> to determine a state of the solenoid switch <NUM> and output a signal indicative of the state of the solenoid switch <NUM> to the controller <NUM>. Similarly still, the braking BIT circuit, can include a current sense resistor <NUM> disposed between the brake resistor <NUM> and the braking switch <NUM> configured to sense a current flowing through the braking circuit <NUM> to determine a state of the brake switch <NUM> and output a signal indicative of the state of the brake switch <NUM> to the controller <NUM>.

The controller <NUM> can include one or more comparators where, upon receiving each of the aforementioned state signals, one or more of the comparators can be configured to compare each of the signal indicative of the state of the common switch <NUM>, the signal indicative of the state of the solenoid switch <NUM>, and the signal indicative of the state of the brake switch <NUM> to a respective reference state to determine if a fault has occurred in any of the starter circuit <NUM>, the solenoid circuit <NUM>, and/or the brake circuit <NUM>. For example, a BIT circuit state table for all possible states of the switches is shown in table <NUM>.

If the BIT circuit is in any of states <NUM>-<NUM>, any fail in a given condition will output a BIT result of short circuit. IF the BIT circuit is in any of states <NUM> or <NUM>, any fail in a given condition will output a BIT result of open circuit. If the BIT circuit is in any of states <NUM> or <NUM>, any fail in a given condition will output a BIT result of either short circuit or open circuit.

Because the common switch <NUM> controls electrical communication from the bus <NUM> to both the solenoid circuit <NUM> and the braking circuit <NUM>, if the common switch <NUM> is OFF (i.e. <NUM>), then both the solenoid BIT circuit and the braking BIT circuit should see no current flow therethrough, regardless of the state of the solenoid and brake switches <NUM>, <NUM>. Therefore, if a current is sensed in either of the solenoid BIT circuit or the braking BIT circuit across the respective current sense resistor when the common switch <NUM> is in state <NUM>, a short circuit will be indicated by the controller. A similar logic can be applied for the remaining states, when the common switch <NUM> is in ON (i.e. <NUM>).

In accordance with at least one aspect of this disclosure, a method, can include supplying a direct current from an electrical bus (e.g., bust <NUM>) to a solenoid circuit (e.g. circuit <NUM>) and a braking circuit (e.g., circuit <NUM>) through a common switch (e.g., switch <NUM>), inverting the direct current to an alternating current, and driving an electric machine (e.g., electric machine <NUM>) with the alternating current to start an engine (e.g., engine <NUM>).

In a starter mode, i.e. when starting the engine, the method can include, maintaining the common switch in an ON state, energizing an inductor coil (e.g., coil <NUM>), and placing a solenoid switch (e.g., switch <NUM>) in an ON state to connect an inverter (e.g., inverter <NUM>) to the electric machine to power the electric machine.

In a braking mode, i.e. when the engine is running at operational speed and the starter is no longer needed, the method can include placing the solenoid switch in an OFF state to de-energize the inductor coil, placing a freewheeling diode (e.g., diode <NUM>) in an ON state to provide a path for decay of current through a inductor coil and monitoring a voltage of the electrical bus. The method can further include, placing a brake switch (e.g., switch <NUM>) in an ON state when the voltage of the electrical bus exceeds a predetermined voltage threshold to connect a brake resistor (e.g., resistor <NUM>) of the braking circuit to ground and continuing to monitor the voltage of the electrical bus. The method can further include placing the brake switch in an OFF state when the voltage of the electrical bus drops below the predetermined voltage threshold.

In embodiments, an idle mode can include placing all of the common switch, the solenoid switch, and the braking switch in an off state to prevent any current from being supplied from the electrical bus to the electric machine.

Conventionally, the solenoid drive control and braking control of an electric machine (e.g., motor) regeneration energy are provided in two separate circuits, each with respective drives. Embodiments combine these two circuits together to reduce total number of components for the system <NUM>, as well as reduce area used on the circuit board and the cost of the circuit altogether. Embodiments of the described common drive approach can also reduce the firmware implementation burden and combine the high side current sensing.

As shown in <FIG>, the circuit <NUM> includes one less IGBT than a conventional circuit of this kind. Because the high side switches are connected to the same DC line for both circuits (e.g., the brake and circuit), and a gate pulse for both switches is the same for all conditions in which the starter is operational, it is possible to eliminate one of the IGBTs, and share a common IGBT (e.g., common switch <NUM>) for both circuitries. One having ordinary skill in the art would appreciate embodiments of the topology described herein can utilize a working principle similar to conventional topology without compromising the functionality of any block, for example as explained in more detail below.

In embodiments, the common switch <NUM> is always ON, so control of solenoid inductor coil <NUM> energization will be decided by the solenoid switch <NUM>. As the solenoid switch driver <NUM> receives the control signal from the controller <NUM>, the switch driver <NUM> will turn on the solenoid switch <NUM> which will consequently solenoid inductor coil <NUM>. This will aid in establishing the electrical connection between the inverter and the electric machine. Importantly, the solenoid switch <NUM> is turned ON before the inverter <NUM> is turned ON. Thus, when the inverter <NUM> is commanded to turn ON, electrical power can reach the motor without any interruption. Upon receiving the OFF signal from the controller <NUM>, the solenoid switch drive <NUM> will turn the solenoid switch OFF and the solenoid inductor coil <NUM> will de-energize. The freewheeling diode <NUM> will turn ON and provide a path for decay of current through the solenoid coil <NUM>.

When the electric machine <NUM> is then commanded OFF (e.g., when it is no longer needed for starting), the energy generated by rotation of electric machine <NUM> due to inertia will feed back to the source (e.g., the electrical bus <NUM>), making the electric machine <NUM> behave as a generator. This will cause a voltage rise on the bus <NUM>, and, if this voltage is not controlled, the voltage increase could rise to levels causing permanent damage on the IGBTs and other components within the circuit <NUM>.

Because the common switch is always ON, a first of the brake resistor terminals 122a will always be connected to a +Vdc input line. To dissipate excess energy across the electrical bus <NUM> (e.g., a DC link capacitor as shown), the braking switch <NUM> should be pulled to the RTN return path. The turning ON and OFF of the brake switch will be based on a voltage monitoring circuit of the electrical bus <NUM>. As the bus voltage rises to a certain level, e.g., with respect to a given voltage threshold, the brake switch <NUM> will receive a high pulse and will connect a second of the brake resistor terminals 122b to ground, allowing energy to dissipate across the brake resistor <NUM>, instead of the electrical bus <NUM>, to reduce the voltage across the bus <NUM> level to safe limit (e.g., below the threshold). Once the bus voltage reduces to safe limit, the brake switch <NUM> will turn OFF and no current will flow through the braking circuit <NUM>.

The control and driving of the common switch <NUM>, the solenoid switch <NUM> and the brake switch <NUM> can include using pulse width modulation (PWM) output from the controller <NUM> and/or the gate drivers <NUM>, <NUM>, <NUM>. For the solenoid switch <NUM>, as shown in <FIG>, each PWM pattern is calculated by comparing a demand value with a triangular waveform of the appropriate frequency. Here, the common switch <NUM> is always high throughout the operation of the starter <NUM>. Therefore, only one triangular signal used to generate the PWM. Because of this, triangular waveform for the operating frequency will be compared with a reference voltage. The value of the reference voltage will be dependent on solenoid current requirement. As discussed above, the solenoid switch <NUM> will only be ON when both the common switch <NUM> and the solenoid switch <NUM> have high pulse. This can be seen in <FIG>, where Vin is the triangular waveform which will be compared with Vref_1 to generate PWM pulse for turning ON the solenoid switch <NUM>. <FIG> shows the solenoid PWM waveform. Here, Verf_1 amplitude tunes such that the solenoid hold on current will be 1A, where <NUM> frequency of triangular signal. <FIG> shows the solenoid current waveform. As can be seen in <FIG>, it is clear that solenoid coil <NUM> is energizing only when both switch pulse high.

With reference now to the braking circuit, as shown in <FIG>, the assumption is made that a given electrical bus voltage range is 500Vdc to 650Vdc and the brake resistor trigger point is 700Vdc. <FIG> show the brake circuit <NUM> PWM generation, the brake circuit <NUM> PWM waveform, and the brake resistor <NUM> current, respectively. As can be seen in <FIG> and <FIG>, using the assumption, the high electrical bus voltage is scaled down to a measuring voltage range 3V to 5V which will be compared with reference voltage (equivalent to 700Vdc threshold). Once the electrical bus <NUM> voltage crosses the threshold limit, the output of comparator will be high, thus turning on the brake switch <NUM> to allow the brake resistor <NUM> to start dissipating extra energy consumed by electrical bus <NUM>, lowering the bus voltage to a safe value. The period of ON state for the brake switch <NUM> will depend on the time needed to lower the bus voltage below the voltage threshold.

<FIG> show an example circuit and the representative waveforms for an assumption of a given bus <NUM> having a voltage range of 500V to 800VD, the brake resistor <NUM> trigger point of 700VDC and a solenoid switching frequency of <NUM>.

The BIT scheme can be a combination of high and low logic signals on the switches which will allow identifying faults within the solenoid circuit <NUM>, braking circuit <NUM> and respective monitoring circuits. Effectively, there should not be any current flowing through the sense resistors during states <NUM>,<NUM>,<NUM>, and <NUM>. If there is, then one of the devices may have failed due to short circuit or the load may have failed short to a chassis, for example. Current flow should be seen in state <NUM> where both switches are closed for solenoid and brake resistor. If there is no current flow, then one of the devices may be stuck in open circuit state. Each of the current sense resistors <NUM>, <NUM>, <NUM> will measure each current Itot (total current across the starter circuit resistor <NUM>), Isol (current across the solenoid circuit resistor <NUM>), Ibr (current across the braking circuit resistor <NUM>). The current data is fed to the controller <NUM> to check the health of the circuit as a whole. If any of the conditions outlined above in table <NUM> fail, then there is either open or short circuit in the system <NUM>.

As described, embodiments can eliminate one an IGBT and instead share a common for both the sections on the high side. This reduces part number and overall net cost, and increases real estate on a printed circuit board. In embodiments, the BIT circuit(s) is the interface between controller circuitry and provides functional checks such as drive signal integrity, solenoid coil functionality and accuracy of brake resistance value. Because one less IGBT is used, one less driver is needed, which reduces the overhead on the BIT circuit. Similar advantages can be realized by the processor such as increased speed due to reduced overhead. By eliminating an entire drive circuit, the processor is required to send one less control signal, freeing up an additional I/O port.

Embodiments provide for a reduction in sense resistors for short detection. Because the high side switch is common to both circuits, only one sense resistor is used for detecting short between terminal (solenoid terminal) with itself or with ground. So, control circuit is become as there is only one single resistor. Embodiments having the topology described herein, a considerable amount of space in the PCB is being saved and the net materials cost is also reduced, without sacrificing functionality of the system. This topology could thus provide distinct technical advantages as an alternative over the present topology in engine starter systems.

As will be appreciated by those skilled in the art, aspects of the present disclosure may be embodied as a system or as a method. Accordingly, examples of this disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects, all possibilities of which can be referred to herein as a "circuit," "module," "controller," or "system. " A "circuit," "module," "controller," or "system" can include one or more portions of one or more separate physical hardware and/or software components that can together perform the disclosed function of the "circuit," "module," "controller," or "system", or a "circuit," "module," "controller," or "system" can be a single self-contained unit (e.g., of hardware and/or software). Furthermore, some examples not part of the invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

Claim 1:
A system, comprising:
a starter circuit (<NUM>) configured to provide power to an electric machine (<NUM>) to drive a load, the starter circuit including:
a voltage input (<NUM>) provided to the starter circuit via an electrical bus (<NUM>);
a common switch (<NUM>) electrically connected to the voltage input via the electrical bus;
an inverter (<NUM>) electrically connected between the starter circuit and the electric machine;
a solenoid circuit (<NUM>) electrically connected to the voltage input via the common switch (<NUM>), wherein:
the solenoid circuit (<NUM>) is configured to provide power to the electric machine via operation of a solenoid switch configured to establish an electrical connection between the inverter and the electric machine,
wherein the solenoid circuit comprises a solenoid built-in-test, BIT, circuit, the solenoid BIT circuit configured to determine a state of the solenoid switch; and
a braking circuit (<NUM>) electrically connected to the voltage input via the common switch, wherein:
the braking circuit is configured to prevent power generated by the electric machine from reaching the electrical bus; and the braking circuit comprises a braking built-in-test, BIT, circuit, the braking BIT circuit configured to determine a state of a brake switch within the braking circuit.