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To ensure proper operation of the aspirating and dispensing apparatus, the air pump 70 provides a relatively low air flow at the output port 72a of the accumulator To provide such an air flow connecting member 24 vents a portion of the flow from air pump The vent tube 76 may preferably be provided as part of the coil 73 e. The vent 76 establishes an upper pressure limit to which the pump 70 will be exposed even in the case of complete occlusion of the sample probe.
The accumulator 72 may also be implemented using other techniques well known to those of ordinary skill in the art. The accumulator output port 72a is coupled through a bleed valve 14 to a common port 80a of pump valve 80 corresponding to pump valve The pump valve 80 also includes a normally open port 80b to the sample probe and a normally closed port 80c to a vent 80d.
The pump valve 80 is controlled by a controller The port 80b of pump valve 80 is coupled to a first port 82a of a three port connecting member A second port 82b of the three port connecting member 82 is coupled to a diluter The diluter 84 may be provided for example as a syringe pump in which the movement of a piston 86 in a first direction forces fluid from a housing 88 while movement of the piston 86 in a second opposite direction pulls fluid into the housing 88 through port 82b.
A shaft 90 couples the piston 86 to a linear stepper motor In response to signals received from controller 94, the stepper rotor 92 drives the piston 86 in first and second opposite directions within the housing In a preferred embodiment, the controller 94 is provided as a microprocessor based controller. A third port 82c of the three port connecting member 82 is connected to a tube 96 having an inner diameter which fits the port 82c sealing the connection.
A pressure transducer 98 has a first port 98a coupled to a second end of the tube 96 and a second port 98b coupled to a first end of a typically resilient tube A second end of the tube is coupled to a first port of a sample probe Thus the connecting element 82 and tubes 96, and pressure transducer 98 provide a fluid path between the sample probe and the pump valve 80 and diluter The pressure transducer 98 is here provided as a flow through pressure transducer of the type manufactured by the Micro Switch Division of Honeywell Corporation and identified as a 26PC Series pressure transducer and more particularly as part number 26PC BFG 6G.
Other flow through pressure transducers having suitable fluid and electrical characteristics may also be used. To facilitate connecting of the transducer ports 98a, 98b to the respective ones of the tubes 96, with substantially different diameters, each of the ports 98a, 98b has coupled thereto a mating tube The mating tubes are provided from a relatively flexible material having a relatively high elasticity characteristic and a non-stretched diameter selected to accept the outside diameter of the tubes 96, with a slight interference fit.
The sample probe includes a probe body having a channel between a first fluid port a to which the system tubing is coupled and having a second fluid port b to which a sample probe tip is coupled. In this particular embodiment, the sample probe tip is provided as a disposable sample probe tip which is removably coupled to the sample probe body It should be appreciated, however, that in some applications it may be desirable to provide the sample probe tip as a non-disposable plastic tip which is permanently secured to the sample probe body The tube which couples the transducer 98 to the sample probe is here provided having a length typically of about nine and one-half inches.
It is desirable to minimize the distance between the sample probe and the pressure transducer In some applications, it may be desirable or even necessary to place the pressure transducer 98 closer than nine and one-half inches from the sample probe and as close as possible to the sample probe In applications in which it is desirable to maximize sensitivity of the apparatus 66 to small changes in pressure, for example, it would be desirable to directly mate the transducer 98 to the sample probe In practical applications, however, it is often not possible due the size of circuit components and available packaging space to achieve this goal.
Thus, as trade-off, the pressure transducer 98 should be coupled to the sample probe via a tube which minimizes the length of the fluid path between the transducer 98 and the sample probe For this purpose the pressure transducer 98 may be disposed on a printed circuit board PCB coupled to the sample probe or as mentioned above, if space permits the pressure transducer may be directly disposed on the sample probe In this particular embodiment the flow through pressure transducer 98 has a pair of electrical terminals 98c, 98d one of which corresponds to a positive output terminal and one of which corresponds to a negative output terminal of the transducer The transducer 98 provides a differential output voltage on the output terminals 98c, 98d representative of the pressure difference between the pressure in the sample probe tip and an ambient atmospheric pressure.
The transducer 98 is electrically coupled through lines to a detector circuit at a pair of input terminals a, b. The detector circuit receives input signals from the pressure transducer and provides at its output terminals output signals to controller 94 and to the air pump In operation, prior to aspirating a sample fluid from a tube 27 or cuvette 32, the vent port 80c of pump valve 80 is initially closed and the common and sample probe ports 80a, 80b are initially open.
Also, the vent port of the bleed valve 78 is closed and the piston 86 is positioned so that no fluid is inside the housing The air pump 70 is then turned on, forcing air through a fluid path which leads to the sample probe tip a. Thus air is forced out of the sample probe tip at a predetermined rate which creates a predetermined pressure measured by Pressure Transducer The sample probe is moved toward a region in which fluid is expected to be contacted such as in the tube When the sample probe tip a initially contacts fluid, the tip a is occluded by the fluid.
This results in the fluid conduit coupled between air pump 70 and the sample probe , including fluid lines 96, , being pressurized. The pressure transducer 98 senses the increased pressure level and provides a transducer signal to the detector circuit The detector circuit then provides a control signal to the controller 94 which stops the sample probe from being lowered further or beyond a preset point into the fluid sample.
The controller 94 provides control signals to open the vent port of the bleed valve 78 to thus de-pressurize the fluid path between the air pump 70 and sample probe including the fluid path in which the pressure transducer 98 is disposed.
After the fluid lines have been de-pressurized, the controller 94 closes the vent port of the bleed valve De-pressurizing the fluid path between the diluter 84 and the connecting member 82 prior to moving the piston 86 improves the ability of the system to accurately determine the aspirate and dispense fluid volumes.
If the fluid path between diluter 84 and connecting member 82 were pressurized when the piston 86 began to move the diluter 84 would initially be forced to overcome the pressure built up in the fluid path. Thus, rather than aspirating fluid in response to movement of piston 86, pressure in the fluid path between the diluter 84 and sample probe would be equalized with the pressure in the diluter, otherwise it is relatively difficult to precisely determine the amount of fluid which was drawn in by the diluter However, by opening and then closing the bleed valve 78 the pressure in the fluid line is set to atmospheric pressure.
Thus, fluid can be immediately drawn into the sample probe tip in response to operation of the diluter The apparatus also detects leaks in the fluid paths. To detect leaks, the sample probe tip a is completely occluded and the tubing is pressurized by turning on the pump The probe tip a is occluded and the pump 70 is left on. The pressure in the fluid path between sample probe and connecting member 82 is thus allowed to rise to a predetermined limit established during a calibration routine.
If no leaks exist, then the pressure will rise to substantially the same calibration level each time the sample probe is occluded. If a leak exists, however, the pressure will not rise to substantially the same level each time. For each system a calibration routine will be performed whereby the tip is occluded and the pressure to which fluid in the fluid paths rise is determined.
The tip a may be occluded, for example, by placing a calibration tip onto the sample probe body Such a calibration tip would be provided having an opening in one end thereof to be attached to the sample probe port b and no opening in the second end thereof.
The system controller 94 would then perform a sample probe calibration routine to establish a threshold pressure and voltage. The transducer detects pressure changes which result in the fluid path due to the occurrence of particular events. For example, the transducer senses pressure changes which result from a number of events including, but not limited to some or all of the following: a fluid leaks in a fluid path; b contact between a sample probe tip and a surface of a fluid; c aspiration of air through a sample probe; d obstruction of a sample probe tip; and e attachment and detachment of a sample tip to a sample probe.
In response to each of these events, the flow through pressure transducer provides a corresponding differential voltage signal to an amplifier circuit at input terminals a, b. The amplifier circuit receives the differential signal fed thereto from the pressure transducer and provides an amplified single ended output signal at an output terminal c thereof. The amplified output signal is fed to an input terminal a of a signal conditioner and pump control circuit A plurality of event detector circuits , , , and are coupled to an output terminal b of the signal conditioner and pump control circuit to receive a pressure signal and a pump servo integrity circuit is coupled to an output terminal c of signal conditioner and pump control circuit While each of the circuits , , , and will be described further below in general each of the circuits , , , and receives an input signal from signal conditioner and pump control circuit at respective input terminals a, a, a, a and a thereof and compares the signal level of the input signal to one or more threshold signal levels internally generated.
Each of the circuits , , , and may be provided having different threshold signal levels. Circuit may be software implemented or otherwise as may be effective In response to the input signal having a signal level either greater or less than the threshold signal levels, each of the circuits , , , , , and provide representative output signals at the output terminal thereof. Each of the output terminals b, b, b, b, b, and b are coupled to controller 94 described above in conjunction with FIG.
The output signals indicate whether or not a particular event occurred or the status of the aspirate-dispense apparatus. It should be noted that each of the circuits , , , , and and may be implemented via a programmed microprocessor or alternatively may be implemented via comparator circuits.
An output terminal d of the signal conditioner and pump control circuit is coupled to an air pump corresponds to pump The leak detector circuit receives the signal on line b and detects whether any leaks exist in the fluid paths of the apparatus FIG.
When operating in a leak detection mode the controller 94 FIG. Leak detector circuit measures the signal level of the signal on line b and in response to the signal level detector circuit provides a signal to controller The signal level of the line b signal indicates to controller 94 whether or not a leak exists in the fluid paths of apparatus Fluid level detector circuit detects when the distal end a of the sample probe tip physically contacts and is inserted into a sample fluid.
Aspirate integrity detect circuit detects whether or not pump valve 80 is operating correctly. After a tip is placed on the sample probe, the sample probe port 80b of pump valve 80 FIG. This should result in a pressure change to a predetermined level.
If there is a leak in the tubing or the sample probe port 80b did not close, then the pressure change will not reach the proper level. Thus the aspirate integrity detect circuit indicates whether or not the pump valve 80 has worked correctly. Clot detector circuit detects whether or not the sample probe tip was occluded during aspirate and dispense operations. In those applications where probe tip is provided as a plastic disposable probe tip, tip detector circuit detects when the probe tip is coupled to and decoupled from the sample probe body based on a change in pressure to predetermined levels in each case.
Pump servo integrity circuit monitors the voltage signal used to servo the air pump and determines whether or not an appropriate servo voltage is being applied to the pump An incorrect voltage would indicate an error in condition such as a blocked flow path. By examining detector signals provided from detector circuits , , , , and , a number of failures in the aspirate and dispense apparatus of FIG. For example, a failed pressure transducer, a failed air pump or a bleed valve stuck in the open position i.
A bleed valve stuck in the closed position i. Similarly, the b signal may be examined to detect if the sample probe port of the pump valve is stuck in the open position so as to continuously provide air from the air pump 70 FIG. A pump valve stuck in the closed position such that the pump valve fails to provide air to the sample probe may be detected by examining the b and b signals.
A leak in the tubing large enough to affect dispense performance or the level sense operation may be detected by examining the line b, b and b signals. It should be noted that each of the event detector circuits , , , , and compares the respective input signal fed thereto to internally generated threshold voltage levels to determine the occurrence or non-occurrence of particular events.
In response to the compare operations, each of the event detector circuits , , , , and provides an appropriate output signal to controller The input to the signal conditioner and pump control circuit is coupled through a resistor to an inverting input of an inverting amplifier The inverting amplifier provides the line b signal to the detectors , , , and A resistor R1 and capacitor C1 are coupled in a negative feed-back path as shown between the output terminal of the inverting amplifier and the inverting input terminal of the amplifier A non-inverting input of the inverting amplifier is coupled to a first terminal a of a sample and hold circuit A charge storing capacitor for the hold function is coupled between a second terminal b of the sample and hold circuit and ground.
A third terminal c of the sample and hold circuit is coupled to an output terminal of a second inverting amplifier and a fourth terminal d of the sample and hold circuit is coupled to the system controller The non-inverting input of the second inverting amplifier is coupled to ground and the inverting input of the amplifier is coupled through a resistor R2 to the output terminal of the first inverting amplifier A feedback capacitor C2 is coupled between the output and the inverting input of the amplifier The output terminal c of the first amplifier is also coupled through a resistor R3 to an inverting input of a third inverting amplifier The non-inverting input of the inverting amplifier is coupled to a reference voltage through a voltage divider network having resistors R4, R5 selected in conjunction with the voltage level of the reference voltage such that a predetermined threshold voltage is provided to the non-inverting input terminal b of the inverting amplifier A capacitor C3 is coupled between the output terminal and inverting input of amplifier The output terminal c of the third inverting amplifier is coupled to a first terminal a of a sample and hold circuit A charging capacitor is connected between a second terminal b of the sample and hold circuit and ground.
A third terminal c of the sample and hold circuit is coupled through a resistor R6 to an input terminal c of a voltage regulator circuit and a fourth terminal d of the sample and hold circuit is coupled to the system controller The system controller provides a control signal to the sample and hold circuit causing it to operate in either a sample mode or a hold mode. The voltage regulator has a voltage input terminal a coupled to a reference voltage source A voltage output terminal b of regulator is coupled through a resistor to control pump A zener diode is coupled between the input c and ground clamping the input to not exceed a predetermined voltage.
A resistor is coupled between node and the anode of the zener diode as shown. A switch is coupled between a second terminal of pump corresponding to air pump 70 and ground. In response to a first control signal from controller 94 the switch is made conducting, activating the air pump The sample and hold circuit establishes a reference or normalized voltage level for the signal on line b corresponding to a reference or normalized pressure level in the pressure transducer The sample and hold circuit is placed in sample mode by the controller 94 in which it connects a signal path between the output of amplifier and the non-inverting input of amplifier Amplifier provides an output signal to sample and hold input terminal c.
Amplifier provides a bias signal at its output that is applied to the non-inverting input of amplifier via sample and hold circuit until the signal provided at the output of amplifier is driven to a voltage level corresponding to ground. At this point controller 94 provides a second control signal to sample and hold terminal d which places the sample and hold circuit in the hold mode.
The voltage level of the sample and hold circuit is thus setting a value which causes the line b output to be zero for what ever pressure is sensed. Thereafter the voltage level of the signal on line b is representative of relative pressure changes detected by the pressure transducer. System operation: 1 a system cycle begins with the sample probe FIG.
A control signal from the controller 94 FIG. With air pump off, no pressure exists in the fluid path in which the flow through pressure transducer is disposed. Thus, the pressure transducer provides a differential output signal corresponding to zero pressure to the input terminals of the amplifier FIG. Also with the pump turned off, the voltage regulator and zener diode maintain the voltage at line b at a set voltage level. Furthermore, the output terminal of amplifier provides a voltage level corresponding to the rail voltage.
In response to the control signal, the sample and hold circuit drives output b to zero volts. When the pump is initially turned on the voltage across the pump is at a high voltage. When pump is first turned on amplifier servos the pump voltage so that line b is at the voltage at its noninverting input.
Prior to the pump turn-on, the output of amplifier is at the positive rail driving current through resistor and forcing line c to the zener voltage set by zener This causes a rapid spinning of pump Over time, amplifier servos the loop resulting in its output falling as line b increases with the build up of the pressure signal from transducer At a desired pressure voltage, the sample and hold circuit is caused by controller 94 to hold that voltage for a cycle.
Also, in response to the pump being turned on the pressure in the system fluid lines rises rapidly. The zeroing of output line b procedure of step "2" is repeated here as a very fast recalibration step. The coupling means is further operable in a generating mode of operation for disconnecting the source of electrical power from the first and second power converters and connecting a voltage regulator to the exciter field winding and the input of one of the power converters to the main generator portion armature winding.
Means are coupled to the first and second power converters and operable in the starting mode for controlling the power converters such that the first power converter provides AC power to the main generator portion armature winding and the second power converter provides AC and DC power simultaneously to the exciter field winding.
Preferably, the controlling means comprises means for causing the magnitude of the AC power applied to the exciter field winding to continuously or stepwise decrease during operation in the starting mode until a particular rotor speed is reached. The causing means may also include means for applying only DC power to the exciter field winding after the particular rotor speed is reached. Preferably, the applying means decreases a parameter of the DC power after a further particular rotor speed is reached.
In accordance with the preferred embodiment, the parameter of DC power comprises DC voltage magnitude. Still further in accordance with the preferred embodiment, the first and second power converters comprise first and second inverters, respectively.
The controlling means preferably comprises means for causing the frequency of the AC power applied to the main generator portion armature winding to uniformly and continuously increase during operation in the starting mode. Also preferably, the causing means includes means for detecting rotor position and means for commutating the main generator portion armature winding based upon the detected rotor position. Further, the detecting means preferably comprises a sensorless rotor position detector.
Alternatively, the detecting means may comprise a rotor position sensor. In accordance with another aspect of the present invention, a control for a brushless generator having a main generator portion and a permanent magnet generator PMG includes an exciter having an exciter field winding disposed in a stator and a set of armature windings disposed on a rotor and coupled to a field winding of the main generator portion by a set of rotating rectifiers.
First and second inverters and a rectifier bridge are provided each having an input and an output. Contactors are operable in the starting mode for coupling a source of electrical power to the inputs of the first and second power converters, the output of the first power converter to the set of main generator portion armature windings and the output of the second power converter to the exciter field winding.
The contactors are operable in the generating mode for disconnecting the source of electrical power from the first and second inverters and connecting a voltage regulator to the exciter field winding, the input of the rectifier bridge to the set of main generator portion armature windings and the input of one of the power converters to the output of the rectifier bridge. Means are coupled to the first and second inverters and operable in the starting mode for controlling the inverters such that the first inverter provides AC power to the set of main generator portion armature windings and the second inverter simultaneously provides AC and DC power to the exciter field winding and such that the AC power applied to the exciter field winding decreases in magnitude during operation in the starting mode until a particular rotor speed is reached.
The controlling means are operable in the generating mode for controlling the power converter coupled to the main generator portion armature winding such that AC power is produced at the output of such power converter. The control of the present invention includes a number of components which are used both in the generating and starting modes. This high degree of commonality leads to a desirable system simplification with attendant size and weight reduction. The generator 10 further includes a motive power shaft 18 connected to a rotor 20 of the generator The motive power shaft 18 may be coupled to a prime mover 21, which may comprise, for example, a gas turbine engine.
The generator 10 and the prime mover 21 may comprise portions of an aircraft auxiliary power unit APU or any other power conversion system. The rotor 20 carries one or more permanent magnets 22 which form poles for the PMG Rotation of the motive power shaft 18 causes relative movement between the magnetic flux produced by the permanent magnet 22 and a set of three-phase PMG armature windings including phase windings 24ac mounted within a stator 26 of the generator The exciter portion 14 includes a field winding 28 disposed in the stator 26 and a set of three-phase armature windings 30ac disposed on the rotor A set of rotating rectifiers 32 interconnect the exciter armature windings 30ac and a main generator portion field winding 34 also disposed on the rotor A set of three-phase main generator portion armature windings 36ac is disposed in the stator During operation in a generating mode, the PMG armature windings 24ac are coupled through a rectifier 38, a voltage regulator 40 and a pair of switches 42, 44 to end taps 46a, 46b of the exciter field winding As the motive power shaft 18 is rotated, power produced in the PMG armature windings 24ac is rectified, regulated and delivered to the field winding AC power is produced in the armature windings 30ac, rectified by the rotating rectifiers 32 and applied to the main generator portion field winding Rotation of the motive power shaft 18 and the field winding 34 induces three-phase AC voltages in the main generator portion armature windings 36ac as is conventional.
Often, it is desirable to use the brushless generator 10 as a motor to bring the prime mover 21 up to self-sustaining speed. This operation is accomplished by providing electrical power to the main generator portion field winding 34 via the exciter 14, providing AC power to the main generator portion armature windings 36ac via lines 48ac and suitably commutating the currents flowing in the windings 36ac to cause the motive power shaft 18 to rotate.
In the present invention, this operation is achieved by connecting an external electrical power source 50 to a power conversion system A series of switches 56ac, as well as the switches 42, 44, are moved to the positions opposite that shown in FIG. The power conversion system 54 is operated to supply power as appropriate to the windings 36ac and the winding 28 to cause the motive power shaft 18 to rotate and thus develop motive power. During operation in the generating mode, the switches 56ac are placed in the positions shown in FIG.
Referring now to FIG. The power conversion system 54 also includes a first power converter comprising a main inverter 72 coupled between a DC bus or link having conductors 73a, 73b, a fixed-frequency oscillator 80, and a mode switch The power conversion system also includes a filter 74 and an exciter power converter 76 coupled to the DC bus conductors 73a, 73b. During operation in the generating mode, the switches are in the position shown in FIG.
This power may also be supplied to the exciter power converter 76; however, since the converter 76 is not operated in the generating mode, no power is supplied by the converter 76 to any of the components. The main inverter 72 converts the DC power into constant-frequency AC power which is filtered by the filter 74 and supplied to the load bus The main inverter 72 receives a frequency reference signal developed by the fixed frequency oscillator 80 via the switch The frequency reference signal establishes the operating frequency of the main inverter During operation in the starting mode, the switches 42, 44, 56ac and 82 are moved to the positions opposite those shown in FIG.
In addition, the contactors 71ac are closed. During starting mode, the commutator 84 is coupled to the main inverter 72 via the mode switch 82 and generates a set of inverter drive or command signals which are provided to the main inverter 72 via line 85 to properly commutate the currents flowing in the windings 36ac.
The commutator 84 generates the command signals based on the phase voltages at the main generator portion armature windings 36ac, which are detected by the commutator 84 via lines 87ac, and the phase currents in the windings 36ab, which are detected via a pair of current sensors 88ab and provided to the commutator 84 via a pair of lines 89ab.
It should be noted that the design of the inverter 72 may be conventional in nature. For example, the main inverter 72 may comprise a six switch converter wherein the switches are connected in a bridge configuration together with flyback diodes and wherein the inverter is operated in a current mode of operation in accordance with pulse-width modulated PWM switch control waveforms.
At initiation of operation in the starting mode, AC power is delivered by the main inverter 72 to the main generator portion armature windings 36ac. Further, the exciter power converter 76 delivers combined AC and DC power to the exciter field winding The exciter 14 acts as a rotary transformer having a primary winding comprising the field winding 28 and secondary windings comprising the armature windings 30ac so that AC power is induced in the armature windings 30ac.
This AC power is rectified by the rotating rectifiers 32 and applied as DC power to the main generator portion field winding Interaction of the resulting magnetic fields causes the rotor 20 to rotate relative to the stator 26 so that the motive power shaft 18 is accelerated. The frequency of the AC waveforms applied to the main generator portion armature windings 36ac is continuously and preferably uniformly increased during the start mode in a linear fashion. In addition, the magnitude of the AC voltage applied to the exciter field winding 28 is continuously decreased in a linear fashion during operation in the start mode until a first particular rotor speed is reached to prevent over excitation and thus limit the generator accelerating capability.
Preferably, this AC power is maintained at a substantially constant frequency. Still further, the magnitude of the DC voltage applied to the exciter field winding 28 is preferably continuously and uniformly increased during operation in the starting mode until a second particular rotor speed is reached. Thereafter, the DC voltage magnitude is kept substantially constant until a third particular rotor speed is reached, following which the DC voltage magnitude is decreased with increasing speed.
Following operation in the starting mode, operation may commence in the generating mode, as described above. The boost converter includes an inductor L1, a controllable switch Q1, a diode D1 and a capacitor C1. The controllable switch Q1 is operated to cause the input voltage magnitude appearing on the DC bus conductors 73a, 73b to be boosted to a level as needed to properly energize the exciter field winding A function generator is responsive to the speed of the rotor 20 and provides a linearly decreasing output with increasing rotor speed.
A signal indicative of rotor speed may be developed as described below in connection with the description of the commutator A pulse-width modulator develops a pulse-width modulation PWM control signal comprising a series of pulses having widths which are dependent upon the output of the function generator A gate drive circuit develops a gate drive signal of appropriate magnitude for the controllable switch Q1 from the output of the pulse-width modulator The exciter inverter is operated by an inverter control , which is responsive to a rotor position signal and a phase reference signal.
A signal indicative of rotor position may be developed as described below in connection with the description of the commutator The rotor position signal is supplied to a speed processor which develops a signal on a line representing the speed of the rotor A function generator , similar to the function generator of FIG.
A multiplier modulates a sinusoidal signal developed by a summer and a sine generator with the output of the function generator The summer sums the rotor position signal with the phase reference signal and the sine generator develops a sinusoidal signal at a phase displacement determined by the output of the summer A further function generator develops a DC reference signal based upon the speed signal appearing on the line The function generator provides a substantially linearly increasing output as speed is increased up to the second particular rotor speed and thereafter provides a substantially constant output level until the third particular rotor speed is reached.
Thereafter, the DC reference signal drops in magnitude. The DC reference signal is summed with the output of the multiplier by a summer and, during operation in the starting mode, the resulting signal is passed by a switch to a further summer The signal produced by the summer comprises a current reference signal from which a current feedback signal developed on a line is subtracted. The resulting current error signal is supplied to a comparator which in turn produces control signals which are processed by a gate drive circuit to derive gate drive signals.
In the embodiment shown, the gate drive signals control first and second switches Q2, Q3 of the exciter inverter The exciter inverter further includes diodes D1-D4 wherein the switches Q2, Q3 and the diodes D1-D4 are connected in a half-bridge configuration and wherein the exciter field winding 28 is connected across nodes , A current sensor provides the current feedback signal to the summer described above.
If necessary or desirable, the exciter inverter may be converted to the full-bridge type. As noted above, during operation in the starting mode, the switches Q2 and Q3 and the switches Q4 and Q5, if used are operated to provide AC and DC power to the exciter field winding The magnitude of the AC voltage, which is preferably maintained at a constant frequency throughout the start sequence, decreases in a substantially linear fashion until a certain speed is reached.
Thereafter, only DC power is supplied to the exciter field winding. During the time that AC and DC power are simultaneously supplied to the exciter field winding 28, the voltage developed across the exciter field winding 28 comprises an amplitude modulated sinewave superimposed on a DC level wherein the magnitude of the modulation decreases with increasing speed. In addition, the DC level on which the AC waveform is superimposed increases until the second particular rotor speed is reached following which the DC level remains a substantially constant level until the third particular rotor speed is reached.
Thereafter, the DC level is decreased in magnitude to provide field weakening and thereby permit continued acceleration of the rotor If desired, the comparator may be replaced by a proportional plus gain unit together with a pulse-width modulator for developing appropriate control signals for the switches Q2 and Q3 and, if used, the switches Q4 and Q5. During operation in the generating mode, the switch is moved to the position opposite that shown in FIG.
Commutator 84 FIG. The commutator 84 includes a back-EMF controller , a switch coupled to the back-EMF controller by a set of lines , and a reluctance controller coupled to the switch by a set of lines During operation in the starting mode, commutation or inverter drive signals are provided to the main inverter 72 over lines 85af based on either the differential reluctance between the windings 36ac or the back EMF produced in the generator More specifically, during an initial portion of the starting mode, when the rotor 20 is at low speed and the magnitude of the back EMF generated in the windings 36ac is relatively small, the commutation signals are generated by the reluctance controller , and the switch occupies the position shown in FIG.
When a rotor speed threshold is reached and the magnitude of the back EMF is sufficiently large, the switch is switched to connect the line to the main inverter 72 so that the commutation signals generated by the back-EMF controller are used to drive the inverter Reluctance Controller The reluctance controller and its theory of operation is described in detail below in connection with FIGS.
Referring to FIG. The three-phase windings 36ac are wound about stator poles 26ac while the field winding 34 is wound about a rotor pole The rotor pole 20a has a first end 20a-1 and a second end 20a As shown in FIG. The reluctance, or magnetic path length, between various pairs of the three phase windings 36ac varies as a function of rotor position in accordance with the following equations: R.
The differential reluctance between various pairs of the three phase windings 36ac also varies as a function of rotor position. The differential reluctance is the difference between the reluctance between a first pair of windings and a second pair of windings. For example, the differential reluctance between phase windings 36b, 36c, referred to herein as Rb-c, is the difference between Rab and Rac. It should be appreciated that the differential reluctance Rb-c is zero when the rotor 20 is vertically aligned in FIG.
From equations  and  above, the differential reluctance Rb-c is as follows: R. The inverter 72 includes six controllable transistor power switches T1 -T6 and six flyback diodes D6-D The actuation of the power switches T1 -T6 is controlled by the inverter drive signals provided by the lines 85af, which signals are shown as waveforms WT1-WT6 in FIG. The reluctance controller includes a phase selector which also receives the six drive signals WT1-WT6 on the lines 85af and generates therefrom three switch actuator signals on three lines ac which are used to selectively activate three switches ac, each of which has an input connected to one of the phase windings 36ac.
Each of the switches ac has a first output, shown at the bottom left portion of each switch, which is connected to the noninverting input of a summing amplifier via a line Each of the switches ac has a second output, shown at the bottom right portion of each switch, which is connected to one of three noninverting inputs of a summing amplifier via one of three lines ac.
At any given time during the starting mode of operation, there is current flowing through exactly two of the three phase windings 36ac, with the third phase winding having no current passing therethrough, or being "unenergized. The phase selector generates the switch actuator signals on the lines ac so that the voltage generated on the unenergized phase winding, resulting from transformer coupling of such winding to the energized phase windings, is provided to the noninverting input of the summing amplifier This is accomplished by causing the switch connected to the unenergized phase winding to connect its input to the output shown at the bottom left portion of the switch.
If the phase winding to which a switch is connected is energized, the switch input is connected to the output shown at the bottom right portion of the switch, so that the voltages on the two energized phase windings are provided to two of the noninverting inputs of the summing amplifier The switch positions as shown in FIG. The switch actuator signals generated by the phase selector on the lines ac are designated S1-S3, respectively, in FIG. The switch actuator signal S1 has a high value when neither waveform WT1 nor WT4 has a high value; the signal S2 has a high value when neither waveform WT3 nor WT6 has a high value; and the signal S3 has a high value when neither waveform WT2 nor WT5 has a high value.
In operation during the starting mode, two of the three windings 36ac are energized, leaving the third winding unenergized. The switches ac are repeatedly switched, as described above, so that the voltage on the unenergized winding is always provided to the noninverting input of the summing amplifier via the line and the voltages on the energized phase windings are always provided to the summing amplifier The amplifier sums the voltages of the two energized windings, and the sum is provided to a divider which divides the sum by the number of energized phase voltages used to generate the voltage sum, which in this case is two, to generate an average phase voltage signal.
The voltage on the unenergized phase winding will have a relatively large DC component and a relatively small AC component with a phase or envelope representative of rotor position. For example, if the voltage difference between the lines 73a and 73b is volts, the DC component of the unenergized phase voltage is approximately volts, and the average of the voltages of the two energized phase windings is approximately volts.
The relatively small AC component of the unenergized phase voltage might be one volt peak-to-peak. In order to extract the small AC component of the unenergized phase voltage, which contains the information regarding the angular position of the rotor 20 with respect to the stator 26, the average phase voltage signal generated by the divider is provided to the inverting input of the summing amplifier , where it is subtracted from the unenergized phase voltage, resulting in the AC component of the unenergized phase voltage which is representative of rotor position.
As a result, the rotor position signal generated by the summing amplifier has a frequency and phase the same as the PWM carrier frequency, but the envelope of the signal varies at a much lower frequency with a phase which is representative of rotor position. To extract the lower frequency envelope from the rotor position signal, the output of the summing amplifier is provided to a synchronous demodulator circuit comprising a multiplier and a low pass filter The multiplier comprises a logical inverter and a two-input switch A first input of the switch is connected to receive the rotor position signal from the amplifier , and a second output of the switch is connected to receive an inverted rotor position signal from the inverter The switch is switched at the frequency of the PWM carrier signal to alternately provide at its output the uninverted and inverted rotor position signal.
This particular multiplier circuit is used in the case of a square-wave PWM carrier signal. Other types of multiplier circuits and synchronous demodulator circuits could also be used. The demodulated rotor position signal is generated on a line and provided to a portion of the reluctance controller , shown in FIG.
The clock signal is generated from the output of the comparators , by a 1-of-2 data selector comprising a pair of AND gates , , an OR gate , and an inverter A first binary data select signal is provided to the AND gate via a line and a second binary data select signal is provided to the AND gate via the inverter connected to the line The data select signals, which at all times are complemented with respect to each other, are generated from the least-significant bit LSB of a counter so that the data select signals values switch each time the count of the counter increases by one.
The rising edge of each clock pulse triggers the counter to increase the count, causing the binary value of the least significant bit to change and the magnitudes of the data select signals to switch high and low states.
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