CA2395956A1

CA2395956A1 - Apparatus for continuously variable speed electric motor applications

Info

Publication number: CA2395956A1
Application number: CA002395956A
Authority: CA
Inventors: Nickolas G. Vrionis; Ronald L. Eichorn
Original assignee: Nickolas G. Vrionis; Ronald L. Eichorn; Varidigm Corporation; Gas Research Institute
Current assignee: Varidigm Corp
Priority date: 1999-12-30
Filing date: 2000-12-21
Publication date: 2001-07-12
Also published as: EP1264393A1; AU2290601A; JP2004523189A; WO2001050589A1; US6329783B1

Abstract

An electric motor and its controller are specially adapted for variable speed applications. The stator of the motor has its main windings controlled by triacs. The triacs are placed to allow the main windings to operate in series at low speed and in parallel at high speeds. The firing delay of the operating triacs is controlled in both series and parallel winding operations to aid in smooth operation of the motor. The auxiliary winding is preferably left uncontrolled to contribute a regular sinusoidal component to the windings power at all times. The controller receives the speed command and figures firing delay and outputs triac control pulses at one of a plurality of settings to bring the motor to the selected speed. In this manner a simple, inexpensive, and continuously variable speed motor may be realized with good performance characteristics.

Description

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P A T ~ N F A N ~Il f"!. h " F T~lan [070~i~ 9'~2s-0 ~'~!~a'ex [~J7042~ !T ~-11 and 97Z8~Zt A 14112 - fl_e/poA March 'l 8, 2002 PCT/US00/361~ 18 _1 _ New Description (replaces the former pages 1 and 2) Apparatus for corrtinuousty variable speed eleatria motor applications Field of~he Ipyeptianl The present invention relates generally to electric motors. The present invention relates more specifically to Induction motors utilized in applications demanding a range of variable speeds.
Discussion of the Related Art Many applications for eiectria motors demand variable speeds with a known toad on the motor. For example a blower motor in a household heating. venti-lation and air-conditioning IHVAC) system will typically be a fractional horsepower motor driving a blower unit or fan blade which represents a known load varying regularly by speed in revolutions per minute.
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- 2 = 18. M~rz 2002 inexpensive induction motors are desirably utilized in many applications.
These motors are not particularly well adapted for variable speed usage. Rather they are designed to opetate efficiently only at one best speed and inefficiencies result when trying to run the motor at other than the designed speed. However, many systems, such as the above HVAC applications, would benefit greatly from having a wider range of motor speeds available.
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In the past art, a variable range~of spe~ds from one induction motor was ob-tained through the use of expensive controllers changing the frequency and voltage of the input to the motor windings or by using a multi-tap motor to attain a number of fixed selectable speeds by mechanical switching between the taps.
Expensive controllers such as these were necessary because, as the input to the motor windings strays farther from sinusoidal, motor efficiency and power factor drop while total harmonic distortion rises, resulting in unacceptable noise, heat, efficiency lass, and motor life.
Thus, known motor controllers utilizing inexpensive switching mechanisms, such as triacs, to control power to the motor windings by "chopping" the sinusoidal waveform input were thought to be of limited use in applications of continousty variable motor speed control.
DE 36 0? 162 teaches an electric motor for a rotary pump and a controller for starting the rotary pump having a primary winding (W 1 ), an auxiliary winding (W2), a capacitor (C), a power switch (SO) for turning the electric motor on and off, and two additional switches (S1) and (S2); the operation of which is set to ~ y ~..
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r_.c__.___:i ,n ..r__ ,n.n, . , . 2a - - . 18.. '~f~rz 2002 cooperate with the power switch to establish the operating mode and speed of the electric motor. When the electric rt~otor is started by means of the .power switch (S0), white switch (S2) is closed, then the windings (W1) and (W2) are in series, and the motot has a torsion of M 1, shown in Fig» 2. When switch (S1 ) is open and switch (S2) is closed, while the power switch (S4) is in a shutdown condition, the windings are in parallel and the magnetic flux is sufficiently. high to provide a rotary speed n at the higher torsion M2. Thus, the speed of rotation of the elecuic motors is set between two points based upon whether the windings are in series or parallel.
EP 0 311 031 teaches an electric circuit having a power winding A of an elec-tric motor and an auxiliary winding H connected in series to a capacitor C.
The power winding A is in series with a triac or switch V and parallel to the auxiliary winding H and capacitor C. The triac V is controlled by a control circuit K.
The control circuit K is adapted in such a way that current is supplied to the power winding only in an integral multiple of half cycles ~ x TI2, the connection time t~. The connection time is repeated periodically with a predetermined period r being an integral multiple of half cycles n x T/2. As suggested by claim 1, the operation of the electric circuit is based upon connecting the auxiliary winding permanently and controlling the triac sfl as to connect the power winding in a predetermined sequence given by a predetermined connection time.
In an article entitled "A Single Phase induction Motor Voltage Controller with Improved Performance", J.D. Law, T.A. Lipo, IEEE Transactions on Power Elec-tronics, Vol. PE-1, No. 4, Oct. 1986, pp 240-247; triac control of paired main and auxiliary windings is suggested to run the pairs first in series then in parallel to maintain constant motor speed as the load varies from a tow to a high, or l g=~S~~O.Q2 r _ _ c . . _ . _ . ~ . . n ,..

- zb - 18. Mart 2002 fully rated, load. A constant firing delay angle based on empirical study is Input to the triac controller using DIP switches. The phase delay Is measured with a voltage zero crossing detector and zero current detector. The current hold off angle is then computed and adjusted to make the phase delay and current hold off equal to the predetermined firing delay to maintain constant rated or near rated speed under the varying load conditions to maintain as closely as possible the full speed the motor was designed for.
The present invention Is rather concerned with the opposite effect of obtaining reasonably efficient variable speed for a load of known characteristics with a low cost induction motor and cantraller system.
Summary of t ~e inyention In a variable speed motor application a particular speed is called for according to an environmental demand placed on the motor function, e.g. moving air or other compressible fluids. For example, a thermostat may determine that more conditioned air needs to be moved in a ventilation system, thus requiring an increase in blower unit rotation and concurrent motor speed.
The controller decodes the speed demand signal and determines if the main windings should operate In series or in parallel configuration. !t also determines the firing rate or delay angle, of the triacs to achieve the desired motor speed and greatest motor efficiency at the expected load. The auxiliary windings are preferably left unswitched to provide a constant sinusoidal component to the X1'8 0~~2n02 Cmnf~nac~oit 1R ilim Ifl~fll ..._ ._.,-z_~~_,.

- ~ 2c - t 8. M~rz 2002 input power in order to increase power factor, and tower total harmonic distor-tion in the motor and thereby increase efficiency and reduce noise and heat.
The present invention provides an inexpensive system for obtaining variable speed electric motor operation over known load ranges. The stator main win-dings of the motor are switch-controlled, preferably by triacs, in an exciusive OR function, to run in series at lower speeds and in parallel at higher speeds.
The switch point between parallel and series operation is determined empirically according to the motor usage, or load, and .. .
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F,~of~.,.:, ~R us., mini d~esigued iv= ~ -' c motor filler in the foam of memory such ow a ' co>c np-table or by calculable re ~ . a of as algorithm. Because the load of a blower varies in lmown rotation to the speed of the motor, tha slip can be determined and controlled by adjustment of the &iing delay angle of the triacs with use of only a zero crossing voltage detector for feedback.
S Where fine adjustments arse neccssazyr, a tachonutcrmay be added as a motor speed feedback to the controller to cnsuiu continwousIy variable spend adjustments. Where available, the tachometer may also be used to determine the switch point between series and parallel main winding operations.
BRIEF DESCRIPTION OF THE DRAWINGS
IO Fig. 1 is an overview of a system utilizing a variable speed induction motor _ according to the present invention.
Fig. 2 is an alternate embodiment showing a 2-stage environmental demand apparatus.
Fig. 3 is a schematic illustration of the stator windings and trine placement 15 thereon.
Fig. 4 is a schematic of tha motor controller according to a prefezred embodiment of the invention.
Fig. 5 is a flow chart detailing the scries/parallcl switching and firing delay adjustment operation of the controller.
20 Figs. 6A and 6B show a schematic of an alternative motor controller showing triac control of the auxiliary winding.
Fig. 7 is a schematic showing alternative winding arrangements.
DETAILED DESCRIPTION OF THE PREFERRED ENIBODI'MENTS
Referencing Fig. l, an operational system 11, such as an HYAC system, has 25 speed demand system 13 derived from environmental sensing and control units such as a thermostat or other furnace control apparatus; a motor controller 15 for accepting input from the envirarimer~tal demmand system I3 and outputting control signals to a r~eotor I? which drives a load I9, such as a blower unit, fan blades or other compressible fluid moving mechanisms as represented in Fig. I by a fan blade Z0. A tachametrr 21 such as a Hall 30 effect device or other known angular speed measuring means is placed to measure motor sped and report the speed information back to the motor controller 15.

AMENDED SHEET

The speed demand system 13 is illustrated as having a temperature probe 23 in an air plenum 25 for its sensing unit upon which the speed demand for the motor 17 would be determined and communicated to the motor controller 15. Various known demand systems and operations may be used in the system of the present invention.
Alternatively, referencing Fig. 2, it will be appreciated that an external environmental control unit such as a thermostat 27 may only give the motor controller an on/off signal at which point an internal or separately placed, speed demand system 29, such as one having differential temperature sensors 26, 28 located within the plenum 25, may determine the speed requirements for the motor 17 and report them to the motor controller 15.
Referencing Fig. 3, first and second main windings 31, 33, respectively, and auxiliary winding 35 of the motor 17 are shown connected across a voltage supply 36 as parallel legs 45, 47, 49 respectively of the stator circuit 37 of the motor.
The windings 31, 33, 35 need not have an equal number of turns, as illustrated in Fig. 7. Any or all of the main and auxiliary windings may have an unequal number of turns selected to provide the greatest motor efficiency when operating the motor at a given speed and in a given mode. First and second main windings 31, 33 have first and second triacs 39, 41, respectively, at opposing ends of their parallel legs. A third triac 43 provides a switchable path between the main winding parallel legs 45, 47 to provide in-series operation of the main windings by operating the third triac 43 while the first and second triacs 39, 41 are not operational. While the auxiliary winding leg 49 is shown with a constant capacitor 51, it is envisioned that any known arrangement of start and run capacitors may be utilized with the present invention. The auxiliary winding 49 is preferably left in parallel with the main windings to provide a constant sinusoidal component to the total power in the windings.
Referencing Fig. 4, the motor controller 15 comprises a microprocessor or programmable microcontroller 53 with an internal oscillator, accepting a speed demand 55 input from the environmental demand unit 13 and a tachometer input 57 from the tachometer 21; a rectifying diode 56, a filter capacitor 58, a voltage regulator 59 across AC line power 61, a resistor 63 for establishing zero voltage detection to the microcontroller 53, and first, second, and third opto-isolators 65, 67, 69 for control inputs to the respective first, second and third triacs 39, 41, 43.

The micmproccssor 53 is lnnf~ably a low power device such as model No. , PIC 12C508, available from Microchip Technology Itic~, of Phoenix, Arizama, which draws on the order of I-2 mA. The voltage regulator 59 is also a lower power device preferably drawing less than ImA such as part no. VB408 ficom ST Microelectronics (www.st:com), S and the opto-isolation units 65, 67, 69 such as part No. MOC 3C1Z3 from QT
Optoelccironics Co. of Su~yvale, California, an also low power devices operattng at 5 rnA. By selecting lower power devices, load current of the controller is low and the IR drop required is low resulting in little wasted power or heat thereby allowing the present invention to generate !ow voltage by regulabag the rectified AC power Iine .61 and thus saving the cost of a transformer. Alternately, a resistor divider from the power line may be used to lower the voltage, with about one watt of additional power loss, so that a low voltage regulator may be used The LEDs of the opto-isoIatars, or optically coupled trigger devices 65, 67, 69 are drivaa by a first and second output lines 71, 73 from the microcontroller 53. The 1 S serial winding operation trine trigger device 69 is connected in opposite polarity to the parallel winding ops,~ion trigger devices 65 and 67. Thus, the parallel trigger devices 6S, 67 are exclusively OR'ed with the serial trigger device 69. If both microprocessor outputs 71, 73 are ~eduat all friars 39, 41, 43 arc off. If the first output 71 is high, the parallel winding operation trines 39, 4I will eonduc~t. If the second output ?3 is high, the serial winding operation trine 43 will conduct. Thos, so long as when transitioning between series and parallel winding configuration modes, an operating trine is forced or allowed to have its load current go through zero, i.e. turn off; before selecting the next winding configuration mode, no canditioa~ can operate both modes simultaneously. Thus, there is no danger during power up err software failure of a short across the power line drawing excess curmeat and damaging the trines 39, 41, 43.
Referencing Figs 6A and 68, in an alternative embodiment, a motor controller 75 is easily connectable to a conventional furnace as is manufactured in volume today. A furnace controller, or envirmimcatal dcnnand system, has two 120VAC
inputs to the motor controller. tf the first input 77 is high, i.e. 1ZOVAC present, this eortasponds to the furnace being in the air conditioning mode. Zn the air canditianing mode the demand is for the fan to be at or near; i.e. substsntielly, the maximum motor speed If the second input AMENDED SHEET

79 is high, this cotraspon;" .o the furnace being in the heating mode, and asking the fan to be at a preset speed within the rangy of about sixty to ninety percent of meximtun speed.
These is a third SA
AMENDEf~ SHEET

Claims

f)- whereby, the controller (15, 75) varies the firing rate of the swithcing mechanisms (39, 41, 43) for control of current there-through in both series and parallel operation of the main windings (31, 33) according to the motor speed command from the speed demand unit (13, 29) to yield a variable speed motor (17).
2. The apparatus according to claim 1 further comprising:

auxiliary windings (36) in the stator (37) being in parallel with the main windings (31, 33) and receiving unswitched line current.
3. The apparatus according to claim 1 or 2, wherein the firing rate is determined by lookup table.
4. The apparatus according to claim 1 of 2, wherein the firing rate is determined by calculation in the controller (15, 75).
5. The apparatus according to any one of claims 1 to 4, wherein the controller (15, 75) is digital and has a plurality of choices of firing delay angles.
6. The apparatus according to any one of claims 1 to 5, wherein the controller (15, 75) is digital and has between 2 and 1024 choices of firing rates.
7. The apparatus accoring to any one of claims 1 to 6, wherein there is hysteresis programmed in when switching between series and parallel configurations.
8. The apparatus according to any one of claims 1 to 7, wherein there are power cycles dropped out when switching between speed settings.
9. The apparatus according to any one of claims 1 to 8, wherein the controller has a voltage zero crossing detector (63).
10. The apparatus according to any one of claims 1 to 9, wherein the load is a fan blade.
11. The apparatus according to any one of claim 1 to 10, wherein the system is an HVAC unit.
12. The apparatus according to any one of claims 1 to 11, wherein the switching mechanisms (39, 41, 43) are biased to provide failsafe switching.
13. The apparatus according to any one of claims 1 to 12, wherein the switching mechanisms (39, 41, 43) are triacs.
14. The apparatus according to any one of claims 1 to 13, further comprising a tachometer (21) for providing speed measurement feedback to the controller (15, 75).
16. The apparatus according to any one of claims 1 to 14, wherein the motor is operated in the series operation at over one half its rated speed.
16. The apparatus according to any one of claims Z to 14 further comprising:

a fourth triac in the auxiliary winding tine (49) for putting the motor in the off mode.
17. The apparatus according to any one of claims 1 to 16, wherein at least two sets of windings have different numbers of turns selected to be in a ratio favorable for motor efficiency at a selected speed setting and operation mode of the windings.
18. A method of operating an induction motor comprising:

a) providing a rotor, a stator (37), and a load of known charac-teristics;

b) arranging the coats of the stator in main (31, 33) and auxiliary windings (35);

c) arranging first and second main windings (31, 33) in parallel with a power supply, each parallel winding leg (45, 47) being controlled on an opposing end thereof by a respective first and second switching mechanism (39, 41), and providing a third switching mechanism (43) in a series path between the winding (45, 47);

d) accepting a speed demand signal (55) and translating said speed demand signal (55) to a speed setting number;

e) looking up at least one operational parameter for the switching mechanisms (39, 41, 43) based on said speed setting number;

f) controlling the switching mechanisms (39, 41, 43) whereby when the third switching mechanism (43) is operational the first and second switching mechanisms (39, 41) are not operational and when the first and second switching mechanisms (39, 41) are operational the third switching mechanism (43) is not operational, to operate the windings (31, 33) in series or in parallel, respectively;

g) connecting the switching mechanisms (39, 47 , 43) to a controller (15, 75) for regulating the operation of the switching mechanisms (39, 41, 43); and h) connecting the controller (15, 75) to a speed demand signal (55) for determination of controller action.
19. A method of operating an induction motor according to claim 18, wherein the switching mechanisms (39, 41, 43) being triacs and the operational parameters include determining the triac (43) or triacs (39, 41) to be operational and the firing delay of each operational triac.
20. A method of operating an induction motor according to claim 18 or 19 further comprising:

programming delays in switching mechanism operation when switching from operation of the first switching mechanism (43) to operation of the second and third switching mehanisms (39, 41).
21. A method of operating an induction motor according to any one of claims 18 to 20, Comprising:

- providing a controller (15, 75) for operating the switching mechanisms;

- accepting a speed command (55) at the controller (15, 75);

- translating the speed command (55) to a speed setting level number;

- determining if the current motor speed setting has changed;

- when the current motor speed setting has changed, looking up operational parameters of the switching mechanisms (39, 41, 43), including which switching mechanisms (39, 41, 43) to fire and its firing delay; and - operating the switching mechanisms (39, 41, 43) according to the operational parameters.
22. A method of operating an induction motor according to claim 21 further comprising:

a) determining if the speed setting level number is equal to, greater than or less than a current motor speed setting;

b) incrementing the current motor speed setting if the speed setting level number is greater than the current motor speed setting;

c) decrementing the current motor speed setting speed if the setting level number is less than a current motor speed setting; and d) taking no action with regard to the current motor speed setting if the speed setting level number is equal to a current motor speed setting.
23. A method of operating en induction motor according to claim 21 or 22 further comprising:

providing a load known characteristics on the motor.