WO2000029853A1

WO2000029853A1 - Methods and apparatus for a real-time motor controller

Info

Publication number: WO2000029853A1
Application number: PCT/US1999/027448
Authority: WO
Inventors: John E. Scott
Original assignee: Energy Research And Management, Inc.
Priority date: 1998-11-19
Filing date: 1999-11-18
Publication date: 2000-05-25
Also published as: WO2000029853A8; AU1823300A

Abstract

A motor controller (100) includes a sense and control module (102) used to monitor motor current (110) and voltage requirements to thereby modulate supply current (108) in all four quadrants of the current waveform. An Insulated Gate Bipolar Transistor (IGBT) circuit (106) is driven by a composite pulse derived from the current and voltage waveforms to control the off-time of the resulting power waveform in all four quadrants. A first pulse train is derived from the supply voltage, a second pulse train is derived from the motor supply current, and a composite pulse train is derived from the first and second pulse trains. The composite pulse train is then applied to the IGBT circuit (106) to control off-time as a function of motor load requirements. By closely matching the actual applied current to the actual motor load requirements, the motor's efficiency and lifespan are dramatically improved, and heat generation associated with the motor (120) is greatly reduced.

Description

METHODS AND APPARATUS FOR A REAL-TIME MOTOR

CONTROLLER

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 60/109,061 , filed November 19, 1998, hereby incorporated by reference.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates, generally, to electronic motor controllers and, more particularly, to a high-efficiency motor controller which monitors and controls supply current in all four quadrants of the current waveform.

Background Information

Electric motors, particularly single-phase and polyphase AC induction motors, are used pervasively within consumer appliances, fans, pumps, material handling systems, and the like. Due to the widely varying efficiency of such motors, and the fact that AC motors most often operate well under their design capabilities, it is desirable to provide control schemes which minimize the power loss ~ and reduce the attendant heat loss — associated with their operation. Thus, it is a goal of the motor control industry to match the power supplied to the motor with the power that the motor actually requires. Presently known control schemes are, however, inadequate in many respects.

For example, traditional AC motor controllers employ thyristors and the like to "turn off the supply current, thereby reducing power requirements within a defined area of the supply waveform. Such systems, however, affect only two quadrants of the current waveform. That is, they attempt to modulate the current cosine waveform at two regions within the curve, rather than all four quadrants. As is known in the art, these designs lead to various inconsistencies and control aberrations.

Furthermore, it is common to implement digital control schemes in motor control circuitry. Such systems, while versatile, suffer from significant limitations introduced through sampling delays. That is, current digital control systems are often unable to keep pace with real-time motor requirements introduced by variations in loading.

In addition, digital control solutions typically incorporate a fixed algorithm, and thus treat all motors and applications equivalently. In practical systems, however, such a fixed algorithm is unsuitable in that it results in extremely conservative solutions — i.e., prone to low savings and over-control.

Methods are therefore needed in order to overcome these and other limitations of the prior art. Specifically, there is a need for systems that provide real-time, high efficiency motor control.

BRIEF SUMMARY OF THE INVENTION

The present invention provides systems and methods which overcome the shortcomings of the prior art. In accordance with one aspect of the present invention, a sense and control module is used to monitor motor current and voltage requirements to thereby modulate supply current in all four quadrants of the current waveform. In accordance with another aspect of the present invention, an Insulated Gate Bipolar

Transistor (IGBT) circuit is driven by a composite pulse derived from the current and voltage waveforms to control the off-time of the resulting power waveform in all four quadrants. In accordance with yet another aspect of the present invention, a first pulse train is derived from the supply voltage, a second pulse train is derived from the motor supply current, and a composite pulse train is derived from the first and second pulse trains. The composite pulse train is then applied to the IGBT circuit to control off- time as a function of motor load requirements.

In this way, by closely matching the actual applied current to the actual motor load requirements, the motor's efficiency and lifespan are dramatically improved, and heat generation associated with the motor is greatly reduced.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS The subject invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and: FIG. 1 is a schematic block diagram of an electronic motor controller in accordance with the present invention; FIG. 2 is a schematic diagram showing an exemplary current converter circuit for use in the sense and control module;

FIG. 3 is a schematic diagram showing an exemplary voltage converter circuit for use in the sense and control module; FIG. 4 is a schematic diagram showing exemplary voltage and current thresholding circuits for use in the sense and control module;

FIG. 5 is a schematic diagram showing an exemplary current compensator for use in the sense and control module;

FIG. 6 is a schematic diagram showing an exemplary hybrid driver module and IGBT circuit;

FIG. 7 depicts a series of waveform diagrams illustrative of a method in accordance with the present invention; and

FIG. 8 is a schematic diagram of an exemplary power supply module.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

Systems and methods in accordance with various aspects of the present invention provide a real-time, high-efficiency motor control system providing four- quadrant off-time modulation. In this regard, the present invention may be described herein in terms of functional block components and various processing steps. It should be appreciated that such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, the present invention may employ various analog and digital components to carry out a variety of functions under the control of one or more microprocessors or other control devices. Such general techniques and standard components that are known to those skilled in the art are not described in detail herein.

Referring now to FIG. 1, a motor controller 100 in accordance with an exemplary embodiment of the present invention generally comprises a sense and control module (SCM) 102, a current sensor 110, a power supply module (PSM) 108, a hybrid driver module (HDM) 104, an IGBT circuit 106, suitable connections to A.C. power input 112, and motor output 114 connected to an AC motor 120. In general, the system operates by monitoring, in real time, the current and voltage supplied to motor 120, while at the same time modulating the off-time of IGBT circuit 106 in all four quadrants of the current cosine wave. In this way, the actual power applied to motor 120 more closely matches the actual load requirements, dramatically increasing the motor's efficiency. As detailed below, the present system provides real-time sensing and response to the motor's load requirements using control parameters which automatically track the motor's

More particularly, referring now to FIG. 7, the operating motor is characterized by a current waveform 702 (FIG. 7(a)), and a voltage waveform 704 (FIG. 7(d)). As is known in the art, the amplitudes of these supply waveforms are a function of, inter alia, the load experienced by the motor during operation. It will be appreciated that current waveform 702 is a voltage representation of the motor current produced via current sensor 1 10 (shown in FIG. 1, and described in further detail below).

The current and voltage waveforms are first rectified to produce rectified waveforms 708 and 710 as shown in FIGS. 7(b) and 7(e). A current threshold level 712 is defined with respect to rectified waveform 708 such that the points at which rectified waveform 708 intersects current threshold 712 are used to define the leading and trailing edges (716) of a pulse centered at the zero crossing point (706) of the current waveform. Similarly, a voltage threshold level 714 is defined with respect to rectified waveform 710 such that the points at which rectified waveform 710 intersects voltage threshold 714 are used to define the leading and trailing edges (718) of a pulse centered at the voltage 90° point. The resulting pulses (720 and 722) are then suitably normalized to TTL levels (i.e., 0-5 V) as shown in FIGS. 7(c) and 7(f), and are symmetrically in phase about their center points. Due to the geometry of the sinusoidal waveforms 702 and 704, as the motor current amplitude increases, the width of pulse 720 will necessarily be reduced. Conversely, as the motor current amplitude decreases, the width of pulse 720 increases.

As with current waveform 702, the width of voltage pulse 722 is directly related to the amplitude of voltage waveform 710. In this way, the widths of pulses 720 and 722 are automatically adjusted in accordance with the motor load and the incoming voltage level (i.e., for brown-out protection). The two pulse trains (720 and 722) are then suitably summed in such a way as to form a summed pulse train (724) as shown in FIG. 7(g). A threshold 726 is then defined with respect to the composite waveform. In a preferred embodiment, this threshold lies between the top of the current pulse (720) and the peak voltage of the pulse (i.e., the sum of the current and voltage pulse). In a particularly preferred embodiment, this threshold has a value of between 5-10 volts, preferably about 7.0 volts.

A composite pulse train 732 (FIG. 7(h)) is then defined as shown in FIG. 7(g). Specifically, the leading edge of pulse 732 is defined by the point 728 at which the rising summed pulse train intersects threshold 726, and the trailing edge of pulse 732 is defined by the point 730 at which the trailing edge of the summed pulse is suitably close to or less than the threshold. It will be appreciated that the composite pulse, in this embodiment, is thus slightly asymmetrical about the current zero crossing point, yet extends into all four quadrants with respect to the motor current waveform. Finally, as detailed in further detail below, composite pulse 732 is then used to modulate the off-time associated with the current actually supplied to the motor. That is, as shown in FIG. 7(i), the resulting motor current waveform 734 is effectively turned off in regions 736, thus controlling the waveform in all four quadrants. It should be noted that in this embodiment the peak amplitude of the motor current waveform is compressed in both alternations, thus conserving more unnecessary power.

Having thus given an overview of the operational principles of the present invention, the various components of an exemplary embodiment will now be described in detail. Referring again to FIG. 1, current sensor 110 comprises any suitable apparatus for sensing the current supplied to motor 120 through IGBT circuit 106. As described further below, the current information derived from current sensor 110 is used by SCM 102 to achieve the objects of this invention. In this regard, a variety of conventional current sensors may be employed for this purpose. For example, in the illustrated embodiment, current sensor 110 comprises a Hall-effect sensor used to sense the current through line 109. Suitable sensors include, for example, the model CLN-50 Hall-effect current sensor manufactured by F.W. Bell, Inc. SCM 102 is suitably configured to sense both voltage and current supplied to the motor and, as described in further detail below, to control IGBT circuit 106 (through HDM 104) such that the off-time associated with the motor current output closely matches the requirements of motor 120 during operation. In the illustrated embodiment, SCM interfaces with current sensor 110, PSM 108, and HDM 104 to accomplish this task.

More particularly, FIGS. 2-5 depict a schematic layout of SCM 102 in accordance with a preferred embodiment of the present invention. Referring first to FIG. 2, the output of current sensor 110 (node 202) is connected to a pair of steering diodes (204 and 206). In general, these diodes act to divide the incoming periodic signal into positive and negative components respectively. The positive component enters the non-inverting input (+) of non-inverting operational amplifier 208, and the negative component enters the inverting input (-) of inverting amplifier 212. Suitable gains are applied to the incoming signals via potentiometers 210 and 214. The two signals are then summed by summer amplifier 216 at the non- inverting input. Again, a suitable gain adjustment 218 is used to provide a scaled I_out 220. In this single-phase implementation, output 220 comprises a rectified sign wave corresponding to the current applied to motor 120. The function of the various resistors and voltage sources shown in FIG. 2 are well known to those skilled in the art, and will therefore not be discussed in detail.

Referring now to FIG. 3, a comparable circuit is used to produce a suitable voltage signal 320 (V_out) representative of the motor voltage. That is, a pair of steering diodes 304 and 306 are used in conjunction with a non-inverting amplifier 308 and an inverting amplifier 312 to produce complementary signals which are summed by summer amplifier 316. As with I_out, suitable gain adjustments 310, 314, and 320 are provided to control the amplitude of output 320. Note that the outputs of the circuits shown in FIGS. 2 and 3 correspond to waveforms 708 and 710, respectively, shown in FIGS 7(b) and 7(e).

Referring now to FIG. 4, voltage and current thresholding circuits are suitably employed to produce appropriate pulses having widths in accordance with motor load as mentioned above. More particularly, the voltage threshold is preferably implemented as an operational amplifier 402, wherein the non-inverting input corresponds to the rectified voltage waveform, and the inverting input corresponds to a threshold value set through the use of a conventional voltage divider circuit implemented with potentiometer 404 — one end of which is connected to the +12V supply of amplifier 402. The threshold value should generally be set between 7.0 and 9.0 volts, preferably about 8.0 volts.

Similarly, the current threshold is preferably implemented as an operational amplifier 406, wherein the non-inverting input corresponds to the rectified current waveform, and the inverting input corresponds to a threshold value set through the use of potentiometer 408 connected to the +12V supply. The threshold value should generally be set between 0.5 and 2.0 volts, preferably about 1.75 volts. The outputs of op-amps 402 and 406 are generally rectangular pulses with an amplitude approximately equal to the saturation voltage of the op-amps (i.e., about 10V). Accordingly, voltage divider circuits 420 and 422 are then suitably used to produce TTL outputs (i.e., 0-5V pulses) In connection with the current thresholding circuit, an inverting transistor 410 is used to invert the signal produced by op-amp 406. This is necessary as the output of the op-amp is actually the complement of the desired pulse train.

Referring now to FIG. 5, the outputs of the voltage and current thresholding circuits (412 and 414) are summed at summing amplifier 502 in conjunction with an appropriate gain control 504. The output of operational amplifier 502 generally corresponds to the summed pulse train 724 shown in FIG. 7(g). This summed signal is connected to the non-inverting input of a thresholding amplifier 506. The inverting input is connected to threshold circuit 508, which in this embodiment is implemented with potentiometer 508 connected to the +12 V supply for the op-amp. As mentioned above, this threshold is suitably between 5 and 10 V, preferably about 7 V.

The output of op-amp 506 is connected (through a one-half voltage divider) to the base of transistor 510. The resulting driver output 512 corresponds generally to composite TTL pulse train 723 shown in FIG. 7(h). As described below, driver output 512 is connected to HDM 104 for control of IGBT circuit 106 FIG. 6 shows a preferred embodiment of HDM 104 and IGBT circuit 106. HDM

104 suitably comprises Hybrid Driver Module 604 and DC-to-DC converter module 602, along with conventional capacitors included to provide gate drive requirements. Although a variety of conventional, commercially available integrated circuits may be used, the preferred embodiment employs a model M57958L Hybrid Driver Module manufactured by PowerEx, Inc. DC-to-DC converter module 602 preferably comprises a model M57145L-01 module manufactured by PowerEx, Inc. The data sheets for these two components are hereby incorporated by reference.

The composite pulse train (TTL input 512) is processed by Hybrid Driver Module 604 in order to provide a suitable gate drive 603 to IGBT circuit 106. DC-to- DC converter 602 is used to provide the various voltage levels required by HDM 104. In the illustrated embodiment, DC-to-DC converter 602 suitably provides +15V, - 8.5V, and common (ground) to HDM 104. These voltage levels are required for turn- on and turn-off of components within IGBT circuit 106.

IGBT circuit 106 suitably comprises IGBT 609, IGBT 610, back-to-back diodes 606 and 608, and snubber capacitors 614 and 618. Each of the IGBTs have an associated internal free-wheeling diode 612. In the illustrated common-emitter implementation, the emitter of IGBT 609 is connected to the emitter of IGBT 610, which is tied back to pin 5 (GND) of hybrid driver module 604.

Gate drive 603 corresponds generally to composite pulse 732 shown in FIG. 7(h). This pulse is effectively used to control IGBT 609 and IGBT 610 in order to modulate the current supplied to the motor. More specifically, at any give time, the gates of both IGBT 609 and IGBT 610 are either off or on. If the IGBT's are both

"on," the current path through IGBT circuit 106 depends on the particular alternation. That is, the current travels either: (1) through IGBT 610 and internal diode 612, or (2) through IGBT 609 and internal diode 616. When the gates of both IGBT 609 and IGBT 610 are "off," no current can flow through the circuit as internal diodes 612 and 616 are configured back-to-back.

In this regard, a variety of commercially available IGBTs may be used for this purpose, including model CM3000DY-12H IGBTs manufactured by PowerEx, Inc. The data sheet for this component is hereby incorporated by references. Furthermore, while IGBT components are particularly advantageous in this embodiment, the present invention is by no means limited to the use of IGBTs; one or more other switching components, e.g., bipolar transistors, field-effect-transistors (FETs), and the like may also be employed. PSM 108 is suitably configured to provide power at a variety of voltage levels for use by the various components of the motor controller system. In the illustrated embodiment, PSM preferably supplies separate lines for +5VDC, +/-12VDC, and +18VDC from a 240V AC, 60Hz input. Any number of conventional power supply circuits may be employed. In a particularly preferred embodiment, PSM 108 comprises a circuit as shown in FIG. 8. Briefly, the output of 240V AC 60Hz supply 902 enters a transformer section 904, which feeds first through a bridge rectifier section 907, then through a network of capacitors 905, to a voltage regulator section 906, from which the various DC outputs 908 are derived. It will be appreciated that the present invention may be employed in the context of a variety of AC input conditions, including single phase, three-phase, and other polyphase systems. In the illustrated embodiment, a 240 VAC, 60Hz AC input is used.

Although the invention has been described herein in conjunction with the appended drawings, those skilled in the art will appreciate that the scope of the invention is not so limited. For example, the illustrated embodiment is shown as an exclusively analog system. It is nevertheless possible to implement the present invention in the context of a digital or hybrid digital/analog system. Similarly, while the illustrated embodiment involves a single-phase motor, the disclosed techniques apply to polyphase systems as well. These and other modifications in the selection, design, and arrangement of the various components and steps discussed herein may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAIMS What is claimed is:

L A motor controller apparatus comprising: an electric motor; a power supply configured to supply current and voltage to said electric motor; a control module configured to sense a current waveform associated with said current and a voltage waveform associated with said voltage, and to modulate said current in all four quadrants of said current waveform in accordance with the requirements of said electric motor.

2. The apparatus of claim 1, wherein said control module is configured to derive a first pulse train from said voltage waveform, to derive a second pulse train from said current waveform, and to derive a composite pulse train from said first and second pulse trains.

3. The apparatus of claim 2, wherein said control module comprises an Insulated Gate Bipolar Transistor (IGBT) circuit having an off-time controlled by said composite pulse train.