Patent Description:
<CIT> discloses a four quadrant motor control for a windshield wiper system of an aircraft. The system applies electromagnetic brake for forward and reverse braking.

<CIT> discloses a motor brake control system comprising a brake power switch and a resistor connected between the positive direct current bus and the negative direct current bus. The brake unit starts to work when a brake signal is received. <CIT> discloses a four quadrant motor control system with an emergency brake unit comprising a power transistor and a resistor. The brake unit is switched on upon reaching the maximum DC bus voltage. <CIT> discloses another motor control for a windshield wiper system, comprising a brake unit and implementing a regenerative braking.

<CIT> and <CIT> disclose various velocity profiles for motor control systems.

A windshield wiper system is provided as defined by claim <NUM>.

As disclosed herein a windshield wiper system (WWS) includes a four-quadrant motor control system that directly drives a windshield wiper of an aircraft. Using the four-quadrant motor control system, controlling the speed and position of the windshield wiper is possible in forward motoring, forward braking, reverse motoring, and reverse braking operating regimes. Inboard-to-outboard, and outboard-to-inboard, motions of the windshield wiper are governed by discrete speed profiles tailored to the curvature of the aircraft windshield, expected aerodynamic loads, and mechanical loads. A braking circuit connected between positive and negative direct current buses dissipates back emf produced during forward braking and reverse braking of the motor to protect the aircraft voltage bus. Additionally, controlling the speed and position of the wiper during braking operations reduces peak voltage experienced by the windshield wiper system during the forward-to-reverse or reverse-to-forward wiper transition so that the power is not fed back to the aircraft network and avoids noise injection.

<FIG> is a schematic of windshield wiper system (WWS) <NUM> that includes wiper <NUM>, motor <NUM>, motor drive <NUM>, and controller <NUM>. When driven by motor drive <NUM> and controller <NUM>, wiper <NUM> traverses windshield <NUM> from inboard position <NUM> to outboard position <NUM>, or vice versa, to define wiper sweep S. As shown in <FIG>, windshield <NUM> has a curved profile to accommodate an aerodynamic shape of an aircraft. Motor <NUM> is a three-phase, brushless, direct current (BLDC) motor or a three-phase, permanent magnet, synchronous motor (PMSM). Motor drive <NUM> includes electrical circuitry used to convert a supplied direct current voltage and communication signals received from controller <NUM> into rotation of motor <NUM>.

Controller <NUM> includes one or more processors <NUM> and system memory <NUM> that stores one or more controller routines, subroutines, algorithms, and or speed profile tables for implementing a four-quadrant control scheme of motor <NUM> in cooperation with motor drive <NUM>. Using a four-quadrant control architecture, motor drive <NUM> and controller <NUM> regulate rotational speed and three-phase current delivery to motor <NUM> during forward motoring operation (quadrant <NUM>), forward braking operation (quadrant <NUM>), reverse motoring operation (quadrant <NUM>), and reverse braking operation (quadrant <NUM>).

During forward motoring and reverse motoring operations, the direction of motor rotation coincides with a direction of applied torque. Contrastingly, the direction of motor rotation opposes a direction of applied torque during forward braking and reverse braking. As used herein, the "forward" and "reverse" directions of motor <NUM> correspond inboard-to-outboard sweep of wiper and outboard-to-inboard sweep of the wiper, respectively. However, the "forward" and "reverse" designations of motor <NUM> are arbitrary, the techniques disclosed below being equally applicable to opposite designations.

Processor <NUM> executes the motor control algorithm described in further detail below. Examples of processor <NUM> can include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry.

System memory <NUM> can be configured to store information within controller <NUM> during operation as well as speed profile data and any associated calibration data necessary for proper function of windshield wiper system <NUM>. System memory <NUM>, in some examples, is described as computer-readable storage media. In some examples, a computer-readable storage medium can include a non-transitory medium. The term "non-transitory" can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). System memory <NUM> can include volatile and non-volatile computer-readable memories. Examples of volatile memories can include random access memories (RAM), dynamic random-access memories (DRAM), static random-access memories (SRAM), and other forms of volatile memories. Examples of non-volatile memories can include, e.g., magnetic hard discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

In some examples, processor <NUM> and system memory <NUM> are collocated in a control unit, which itself can be collocated with other components of the windshield system <NUM>. In other examples, any one or more components and/or described functionality of controller <NUM> can be distributed among multiple hardware units. For instance, in some examples, controller <NUM> can be incorporated into an aircraft control module designed to perform functions other than those required by the windshield wiper system <NUM>. In other examples, controller <NUM> can be a module discrete from other aircraft control modules, which may be collocated with or remote from these other aircraft control modules and/or other components of the windshield wiper system <NUM>. In general, though illustrated and described below as an integrated hardware unit, it should be understood that controller <NUM> can include any combination of devices and components that are electrically, communicatively, or otherwise operatively connected to perform functionality attributed herein to controller <NUM>.

<FIG> is a schematic of the motor <NUM> and motor drive components <NUM> of windshield wiper system <NUM>. As shown by <FIG>, motor <NUM> includes first phase 32A, second phase 32B, and third phase 32C arranged in a wye configuration. Motor drive <NUM> includes three-phase inverter <NUM> and break circuit <NUM>.

Three-phase inverter <NUM> includes three half bridges 38A, 38B, and 38C connected in parallel between positive direct current bus <NUM> and negative current bus <NUM>. Phases 32A, 32B, and 32C of motor <NUM> are connected to respective half bridges 38A, 38B, and 38C between respective high-side power switches 44A, 44B, and 44C and low-side power switches 46A, 46B, and 46C. High-side power switches 44A, 44B, and 44C connect between positive direct current bus <NUM> and phases 32A, 32B, and 32C while low-side power switches 46A, 46B, and 46C connect between negative direct current bus <NUM> and phases 32A, 32B, and 32C. Each high-side power switch 44A, 44B, and 44C and each low-side power switch 46A, 46B, and 46C are connected in parallel with one of free-wheeling diodes 48A, 48B, and 48C and free-wheeling diodes 50A, 50B, and 50C, each diode 50A-50C arranged to permit current to bypass high-side power switches 44A, 44B, and 44C from one of phases 32A, 32B, and 32C to positive direct current bus <NUM> and each diode 50A-50C arranged to permit current to bypass low-side power switches 46A, 46B, and 46C from negative direct current bus <NUM> to one of phases 32A, 32B, and 32C. Three-phase inverter <NUM> additionally includes capacitor <NUM> connected between positive direct current bus <NUM> and negative direct current bus <NUM>.

Brake circuit <NUM> includes brake power switch <NUM> and resistor <NUM> connected in series between positive direct current bus <NUM> and negative current bus <NUM>. Like high-side and low-side power switches, diode <NUM> is connected in parallel with brake power switch <NUM>, permitting current to flow from negative direct current bus <NUM> to positive direct current bus <NUM> via resistor <NUM>, bypassing brake power switch <NUM>.

High-side power switches 44A-44C, low-side power switches 46A-46C, and brake power switch <NUM> are depicted as MOSFETs in <FIG>. However, one or more of these power switches can be insulated gate bipolar transistors (IGBTs), silicon carbide (SiC) gate drivers, or another suitable power switch.

Positive direct current bus <NUM> and negative direct current bus <NUM> are connected to voltage source <NUM> via pulse width modulation (PWM) generator <NUM>. Voltage source <NUM> is any suitable voltage source provided within an aircraft. High-side power switches 44A, 44B, and 44C, low-side power switches 46A, 46B, and 46C, and brake power switch <NUM> are connected to controller <NUM> to receive gate signals in accordance with the motor control algorithm disclosed herein.

<FIG> is a diagram illustrating speed profile <NUM> for windshield system <NUM> as wiper <NUM> traverses from inboard position <NUM> to outboard position <NUM>. <FIG> is a diagram illustrating speed profile <NUM> for windshield system <NUM> as wiper <NUM> traverse from outboard position <NUM> to inboard position <NUM>. In each case, profiles <NUM> and <NUM> express the desired or target rotational speed (i.e., angular velocity) of motor <NUM> as a function of time (i.e., seconds). Alternatively, speed profiles <NUM> and <NUM> can be expressed as a function of angular position of motor <NUM>. Speed profiles <NUM> and <NUM> are each nonzero angular velocity distributions that start and end at rest (i.e., angular velocity ω=<NUM>). The starting position and ending position coincide with inboard position <NUM> and outboard position <NUM> of wiper <NUM> depending on the direction the wiper travels across the windshield. Furthermore, speed profiles <NUM> and <NUM> are entirely positive angular velocity or entirely negative angular velocity such that the motor and the wiper do not reverse direction between inboard position <NUM> and outboard position <NUM>.

Speed profile <NUM> includes acceleration phase 62A, constant speed phase 62B, and a deceleration phase 62C. During acceleration phase 62A, angular velocity ω increases continuously from an initial position (i.e., ω<NUM>=<NUM>) to a maximum angular velocity ωmax,<NUM> in an inboard-to-outboard direction of the wiper and motor. Constant speed phase 62B maintains maximum angular velocity ωmax,<NUM> until deceleration phase 62C, at which time angular velocity ω decreases continuously from maximum angular velocity ωmax,<NUM> to an outboard, resting position (i.e., ω<NUM>=<NUM>).

Similarly, speed profile <NUM> includes acceleration phase 64A, constant speed phase 64B, and deceleration phase 64B arranged in sequential order with respect to time. During acceleration phase 64A, angular velocity ω increases continuously from an initial, outboard position (i.e., ω<NUM>=<NUM>) to a maximum angular velocity ωmax,<NUM> in an outboard-to-inboard direction of the wiper and motor. Constant speed phase 64B maintains maximum angular velocity ωmax,<NUM> until deceleration phase 64C, at which time angular velocity ω decreases continuously from maximum angular velocity ωmax,<NUM> to an inboard position (i.e., ω<NUM>=<NUM>).

In some embodiments, one or more of acceleration phase 62A, deceleration phase 62C, acceleration phase 64A, and deceleration phase 64C can be characterized by constant angular acceleration rates as indicated by dashed lines <NUM>, <NUM>, <NUM>, and <NUM>, respectively. In other embodiments, speed profile <NUM>, speed profile <NUM>, or both can be nonlinear within one or more of acceleration phase 62A, deceleration phase 62C, acceleration phase 64A, and deceleration phase 64C.

For instance, acceleration phase 62A includes three subphases 74A, 74B, and 74C arranged in sequential order with respect to time. Increasing acceleration characterize subphases 74A and 74C, which coincide with the beginning and end of acceleration phase 62A. Subphase 74B is intermediate of subphases 74A and 74C, characterized by constant angular acceleration. In other embodiments, acceleration phase 62A can be characterized by continuously increases angular acceleration, albeit at different acceleration rates within subphases 74A, 74B, and 74C.

As depicted in <FIG>, deceleration phase 62C includes five subphases 76A, 76B, 76C, 76D, and 76E arranged in sequential order with respect to time. Subphase 76A begins deceleration at an initial rate that decreases as it transitions into subphase 76B. Within subphase 76B, the angular deceleration rate remains constant until deceleration rate decreases further within subphase 76C. During subphase 76D, the deceleration rate again remains constant until subphase 76E at which time the deceleration rate increases until angular velocity ω<NUM>=<NUM>.

Similar profiles are presented in <FIG> for speed profile <NUM>. Acceleration phase 64A includes three subphases 78A, 78B, and 78C, each analogous to subphases 74A, 74B, and 74C of speed profile <NUM>, albeit occurring over a short time duration and hence at different acceleration rates. Additionally, deceleration phase 64C includes five subphases 80A, 80B, 80C, 80D, and 80E analogous to subphases 76A, 76B, 76C, 76D, and 76E of speed profile <NUM>. Again, subphases 80A-80E may occur over a shorter or longer time durations than corresponding subphases 76A-76E of speed profile <NUM>.

The inboard-to-outboard angular velocity distribution provided by speed profile <NUM> can differ from the outboard-to-inboard angular velocity distribution provided by speed profile <NUM> due to the order in which wiper <NUM> traverses the contour of the windshield as well as due to external aerodynamic loads on wiper <NUM>. During forward flight of the aircraft, air flowing over windshield <NUM> tends to apply torque to motor <NUM> via wiper <NUM> in the direction of rotation corresponding to inward-to-outward motion of wiper <NUM>. Accordingly, less torque is required by motor <NUM>. Similarly, air flowing over windshield <NUM> during flight tends to counteract the motor torque applied to wiper <NUM> for outward-to-inward travel. To counteract the influence of aerodynamic load on wiper <NUM>, constant speed phase 62B of speed profile <NUM> may have a shorter duration than constant speed phase 64B of speed profile <NUM>. Additionally, deceleration phase 62C of speed profile <NUM> can extend over a larger duration than acceleration phase 64A of speed profile <NUM>. Additionally, high curvature regions of aircraft windshields tend to be located toward the outboard ends of wiper travel. As such, deceleration phase 62C of inboard-to-outboard profile <NUM> may require additional time duration and/or different deceleration subphases (e.g., subphases 76A-76E) to accommodate the curvature of windshield <NUM>. Contrastingly, higher acceleration rates may be required within acceleration phase 64C of outboard-to-inboard profile <NUM> to overcome to accommodate the curvature of windshield <NUM> in the opposite direction of travel, which results in a shorter time duration relative to deceleration phase 62C.

<FIG> is a schematic of controller <NUM> and the implementation of motor control algorithm <NUM> stored within system memory <NUM>. Motor control algorithm <NUM> includes speed control loop <NUM> and current control loop <NUM> arranged as outer and inner control loops of motor <NUM>, respectively. Additionally, motor control algorithm <NUM> includes brake control loop <NUM> that operates brake circuit <NUM> during forward braking and reverse braking conditions of windshield wiper system <NUM>. Speed profile tables <NUM> store one or more speed profiles for wiper <NUM> and motor <NUM> (e.g., speed profiles <NUM> and <NUM>) that provide a commanded speed to control loops <NUM>, <NUM>, and <NUM> as a function of time or position of motor <NUM>.

Speed control loop <NUM> includes speed controller <NUM> that receives speed command <NUM> from speed profile tables <NUM> and position feedback data <NUM> from one or more hall sensors, or an encoder. Alternatively, position feedback data <NUM> can be produced using sensorless techniques. For instance, the position of motor <NUM> can be deduced by, for example, monitoring back-EMF of each motor phase. Speed command <NUM> represents the commanded speed and rotational direction of motor <NUM> at a given time step or rotational position of motor <NUM>. For instance, counterclockwise rotation of motor <NUM>, as viewed from its output shaft to wiper <NUM>, can be represented as a positive speed value while clockwise rotation of motor <NUM>, can be represented as a negative speed, or vice versa. Position feedback data <NUM> can be any digital or analog signal representative of a rotational position of motor <NUM> as a function of time. Upon receiving position feedback data <NUM>, speed controller <NUM> determines a rotational speed, or angular velocity of motor <NUM> that is associated with a particular time step and/or position of motor <NUM>. Speed controller <NUM> compares the motor speed determined from position feedback data <NUM> with speed command <NUM> and thereby determines speed error <NUM> of motor <NUM>. Subsequently, speed controller <NUM> utilizes speed error <NUM> to generate speed correction <NUM> based on a proportional (P), proportional-integral (PI), or proportion-integral-derivative (PID) control scheme. Speed controller <NUM> outputs speed correction <NUM> to pulse width modulation (PWM) generator <NUM> to vary a target rms voltage (Vt,rms) supplied to motor <NUM> via positive direct current bus <NUM> and negative current bus <NUM>. PWM generator <NUM> varies the target rms voltage by varying the duty cycle of the voltage supplied to positive direct current bus <NUM> and negative direct current bus <NUM>.

Current control loop <NUM> include current controller <NUM> that receives speed correction <NUM> from speed controller <NUM>, position feedback data <NUM>, discussed above, and phase current feedback data <NUM>. Phase feedback data <NUM> can be any analog or digital signal indicative of first phase current ia, second phase current ib, and third phase current ic of first phase 32A, second phase 32B, and third phase 32C, respectively. Initially, current controller <NUM> determines motor position <NUM> (i.e., the position of the rotor relative to the stator field of motor <NUM>) using the position feedback data <NUM>. Additionally, current controller <NUM> transforms phase currents ia, ib, and ic into quadrature currents qa, qb, and qc and direct currents da, db, and dc using a Clark and Park transformation. Subsequently, current controller <NUM> utilizes a proportional (P), proportional-integral (PI), or proportional-integral-derivative (PID) control scheme or schemes to output quadrature currents corrections (i.e., Δqa, Δqb, and Δqc) and direct currents corrections (i.e., Δda, Δdb, and Δdc) based on speed correction <NUM> and motor position <NUM>. Further, current controller <NUM> maximizes net quadrature current qnet equal to the sum of phase quadrature currents qa, qb, and qc and minimizes net direct current dnet equal to the sum of phase direct currents da, db, and dc in order to maximize torque applied to motor <NUM>. Using a reverse Clark and Park transformation, quadrature current corrections (i.e., Δqa, Δqb, and Δqc) and direct current corrections (i.e., Δda, Δdb, and Δdc) are transformed into first, second, and third phase current corrections (i.e., Δia, Δib, and Δic). Based on the first, second, and third phase corrections, current controller <NUM> determines gate signals G1, G2, G3, G4, G5, and G6 and outputs gate signals G1-G6 to respective high-side power switches (i.e., 44A, 44B, and 44C) and low-side power switches (46A, 46B, and 46C) of three-phase inverter <NUM>, effectively altering the timing of gate signals G1-G6 to commutate motor <NUM> according to the desired speed command <NUM> using maximum motor torque. Speed control loop <NUM> and current control loop <NUM> repeat the foregoing process for each subsequent speed command <NUM> at a predetermined calculation rate.

While speed control loop <NUM> and current control loop <NUM> control the speed and commutation of motor <NUM>, brake control loop <NUM> activates brake power switch <NUM> of brake circuit <NUM> during forward braking and reverse braking operation to dissipate back emf produced by motor <NUM> during braking operation. Brake control loop <NUM> includes brake controller <NUM> and pulse width modulation (PWM) generator <NUM> operatively connected to brake circuit <NUM>. Brake controller <NUM> receives speed command <NUM> from speed profile tables <NUM> and direct current (DC) bus voltage Vbus measured between positive direct current bus <NUM> and negative current bus <NUM>. Based on speed command <NUM> and DC bus voltage Vbus, brake controller <NUM> outputs brake signal Sbrake to PWM generator <NUM>, which converts brake signal Sbrake into a pulse width modulated gate signal G7 delivered to brake power switch <NUM>. Upon receiving gate signal G7, brake power switch <NUM> opens or closes in accordance with the duty cycle of gate signal G7. Accordingly, brake circuit <NUM> can be activated in proportion to the magnitude of back emf produced by motor <NUM> in order to maintain DC bus voltage within a target voltage range of a nominal voltage supplied in accordance with speed control loop <NUM>.

In some examples, brake controller <NUM> triggers brake power switch <NUM> when a change in speed command <NUM> indicates a motor speed decrease and the DC bus voltage deviates from the target voltage commanded by speed control loop <NUM> by more than a threshold amount. In this instance, PWM generator <NUM> adjusts the duty cycle of gate signal G7 in proportion to the voltage difference between the target rms voltage (Vt,rms) output by speed controller <NUM> and DC bus voltage (Vbus) received by brake controller <NUM>. Accordingly, back emf produced by motor <NUM> during braking operation is dissipated by resistor <NUM> of brake circuit <NUM> to maintain DC bus voltage Vbus at the target rms voltage Vt,rms commanded by speed controller <NUM>. Additionally, back emf from motor <NUM> does not propagate into voltage source <NUM> of the aircraft and thereby protects other aircraft systems connected to voltage source <NUM>.

Claim 1:
A windshield wiper system comprising:
a three-phase motor (<NUM>);
a three-phase inverter (<NUM>) comprising a positive direct current - DC-bus (<NUM>), a negative direct current bus (<NUM>), a plurality of high-side power switches (44A, 44B, 44C), and a plurality of low-side power switches (46A, 46B, 46C);
a brake circuit (<NUM>) connected in parallel between the positive direct current bus and the negative direct current bus, the brake circuit comprising a brake power switch (<NUM>) and a resistor (<NUM>) connected in series with the brake power switch;
a controller (<NUM>) operably connected to the three-phase motor, the three-phase inverter, and the brake circuit, the controller comprising a processor (<NUM>) and a computer-readable memory (<NUM>) encoded with instructions that, when executed by the processor, cause the controller to:
transmit first commutation signals to the high-side power switches and low-side power switches to thereby drive the motor according to a first speed profile associated with a first rotational direction of the motor;
transmit second commutation signals to the high-side power switches and low-side power switches to thereby drive the motor according to a second speed profile associated with a second rotational direction of the motor opposite the first rotational direction of the motor; and
transmit a first gate signal to the brake power switch to thereby close the brake power switch, wherein the controller is adapted to send the first gate signal when the first speed profile commands a first speed decrease and a DC bus voltage increases above a first DC bus voltage threshold associated with a first constant speed phase or when the second speed profile commands a second speed decrease and the DC bus voltage increases above a second DC bus voltage threshold associated with a second constant speed phase, the DC bus voltage measured between the positive direct current bus and the negative direct current bus of the three-phase inverter.