WO2003038988A1

WO2003038988A1 - Speed and direction control for capacitor motors

Info

Publication number: WO2003038988A1
Application number: PCT/IL2002/000799
Authority: WO
Inventors: Arthur Naiman; Eli Barnea
Original assignee: Arthur Naiman; Eli Barnea
Priority date: 2001-10-02
Filing date: 2002-10-02
Publication date: 2003-05-08

Abstract

The present invention is directed towards a low cost, high efficiency and multi-adaptable single phase AC induction motor controller. The invention eliminates the need for an external start/run capacitor and uses the additional windings (Ls) of the single-phase AC motor, for continuous speed, direction (forward/reverse) and torque control and regulation. The invention allows the functions of the soft start, soft stop, and dynamic brake to work and enables the motor (100, 200, 300) to run at a higher speed than normal. The motor runs as a two-phase motor by means of the apparatus providing the generation of a circular electromagnetic field in the motor. The present invention improves the performances and the efficiency of single phase AC motors and equipment associated with it, i.e. fans, compressors, pumps, conveyors, robotic controllers etc. Additionally, it will reduce the heat generated in the motor during the steady state operation mode for the full range of speed control. Other benefits of the invention include reduction of the EMI / RFI interferences, improved power factor, energy savings and elimination of the need for additional winding taps for speed variation.

Description

SPEED AND DIRECTION CONTROL FOR CAPACITOR MOTORS

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION

The present invention relates generally to electric motors and, more particularly, to a low cost, high efficiency and multi-adaptable single-phase induction motor control.

2. DESCRIPTION OF PRIOR ART

Various types of single-phase capacitor motors, generally referred to as split motors, are well known in the electro-mechanical field. Currently in the market there is a high demand for motors with power under three (3) horsepower, which amounts to hundreds of million units per year. The proportion of these motors in the total electric machine production (cost- wise) exceeds twenty percent (20%) and is higher than that of hydro- and turbogenerators. Typically, split motors are used in the areas of HVAC, medical equipment, aerospace systems, automotive, marine systems, and the like.

Generally speaking, a split capacitor motor has two windings, a main winding and an auxiliary (or starting) winding. The auxiliary winding uses an additional external capacitor for creating a 90° phase shifted voltage to the auxiliary winding and for providing starting torque needed for the motor. There are three types of split capacitor motors: (i) permanent split capacitor (PSC) motors, (ii) capacitor start motors and (iii) start/run capacitor motors. In all of these motors, the performances of the motors are determined by the design of the motor and its appropriate capacitor.

In view of the foregoing, a need exists to find effective ways of reducing power consumption in single-phase capacitor motors and of providing favorable conditions for consumers using domestic machines. Conventional methods to fulfill this need include applying highly efficient systems to regulate motor velocity. The unique features of single-phase capacitor motor design determine the specific approach to the development of efficient systems for regulating the motor driving gears. For example, single-phase capacitor motors are electrically asymmetric, that is, the motors do not generate circular fields even at nominal rotational speed. As is generally known, and illustrated in FIGS 1A-1D, conventional methods for controlling the speed of a single-phase capacitor motor are to connect additional windings (e.g., Lai, La2, Ls, Lsl, Ls2) to a main winding (Lw). These approaches require a special speed selector to select a desired speed of the motor. Additionally, these approaches typically result in significantly enlarging the motors to produce equal power.

Another conventional method for controlling the speed of the motor is to use phase voltage control to supply a controlled voltage to the motor's windings. This method results in sharp deterioration of the motor's power parameters, e.g., the efficiency in some cases drops down to about sixteen percent (16%) as well as a steep drop in the value of the critical electromagnetic torque of the motor.

An additional conventional method for controlling the speed of a single-phase capacitor motor is based on standard frequency converters. This method is generally known to be efficient for three-phase electric motors. However, the method results in low efficiency, both technically and economically, when implemented in split capacitor motors.

The inventors have found that the above considerations are typically important for developing a system for driving gear regulation in single-phase motors, based on frequency variations. As noted above, conventional systems for controlling the speed of single- phase capacitor motors by means of frequency variations are known. The inventors have found deficiencies in conventional systems in that these systems are not seen to generate a circular field even at a nominal rotational speed. As such, these systems result in low efficiency of motors in all ranges of speed regulation. For example, U.S. Patent No. 5,422,557, issued June 6, 1995, to Jin- Won Lee et al., discloses a method for controlling the speed of a single-phase induction motor using frequency variation. This process involves generating an operation start signal and a speed command signal according to the user's selection. The CPU then selects digital data for the formation of a sinusoidal wave signal of a desired frequency. The sinusoidal wave function based on the digital data is then generated, and compared with a triangular signal used for controlling the speed of a motor. This converts a DC voltage to a frequency band desired by the user to operate the motor. This method for controlling speed may be used only for low power split phase motors. Additionally, the method described by Lee et al. is seen to work only if the auxiliary (starting) winding contains an added capacitor. The added capacitor supplies a ninety degree (90°) phase shifted voltage to the auxiliary winding, thus providing an additional starting torque for the rotor. However, this method for speed regulation of a single- phase motor is very inefficient because the parameters of a capacitor change with the variations in frequency of the supply voltage. If the frequency deviates from about fifty hertz (50Hz), it is impossible to gain a speed regulation with a determined torque without increasing the current in the windings to a value higher than the nominal current. As such, the method described by Lee et al. results in overheating of the motor windings, lower efficiency, noise generation, vibration, and other unwanted phenomena. Anacon Systems, Inc. (Mountain View, CA) provides digital controls for single-phase AC induction motors having the aforementioned perceived deficiencies.

U.S. Patent No. 6,121,749, issued September 19, 2000, to Frank E. Wills et al., describes a system for controlling a motor by providing a device for changing the amplitude and frequency of the main winding, while the amplitude voltage of the auxiliary winding is kept constant. This method is generally referred to as a phase- amplitude method control of a motor. In the Wills et al. system, a change in the frequency of the auxiliary winding changes the voltage and phase of the magnetic flux on the auxiliary winding. However, these parameters also depend on the load of the motor. The voltage on the auxiliary winding is: Ua=U2-Uc=U2-la.Z, where

Ua - vector of voltage on auxiliary winding

U2 - a summary vector of voltage on auxiliary winding and capacitor Uc - a vector of voltage on a capacitor la — a vector of current in auxiliary winding Z — a complex resistance of a capacitor

If the current of the auxiliary winding is changed,due to either changes in the load, changes in the voltage of a main winding or changes of speed (frequency), the voltage drop on the capacitor changes. This effects the voltage of the auxiliary winding and the phase shift between those windings and the main windings. As a result, Wills et al. is not seen to provide a constant circular magnetic field. Therefore, the system described in Wills et al. does not result in stable speeds and torque. A small change of the load will result in a considerable change of a motor speed.

U.S. Patent No. 5J46J47, issued September 8, 1992, to Frank E. Wills et al., describes a system that is seen to work only in special motors, e.g., motors having its two windings conductively isolated from each other (e.g., a PSC motor). In one embodiment, the PSC motor is supplied from a two-phase inverter circuit. The PSC motor is also connected through a four-pole double throw switch to either a single- phase source including a capacitor or the two-phase inverter circuit. This system may provide good results of the PSC motor speed control, but it requires manufacturing special motors and an expensive inverter with eight switches and eight drivers. The system described in the '147 patent does not have an algorithm needed for changing direction (clockwise or counterclockwise) and for determining the voltage levels ratio between the main and auxiliary windings (asymmetric). Additionally, U.S. Patent No. 5,796,234, issued August 18, 1998, to Nick

Vrionis, describes a method for generating split capacitor speed variation of a motor by removing the capacitor and connecting a controller to a first, second and third terminals of the motor. The controller drives the motor to one, two or more predetermined speeds. The controller's driving devices include three voltage drivers, three switching elements and a frequency controller for generating three sets of frequency signals. Each of the three voltage drivers is connected to a DC voltage supply and has an output connected to one of the first, second or third terminals of the split capacitor motor. The frequency controller generates three sets of signals, each controlling one of the voltage drivers and a respective switching elements. Vrionis is seen to describe a system that provides speed regulation for single- phase capacitor motors when the windings are, at certain times, switched 'on' to a supply system and switched 'off from a supply system. Therefore, Vrionis is seen to require "essential frequencies" such that the motor operates smoothly. Accordingly, deficiencies in Vrionis include the need for a special frequency generating means, a minimum of six switches and six drivers. Additionally, Vrionis does not provide a generation of circular electromagnetic fields for the motor and may not be used in cases necessary to continuously regulate the speed of electric drives with different static and dynamic characteristics.

Therefore, a need exists for a low cost, high efficiency and multi-adaptable device for controlling and regulating speed and direction of single-phase induction motors. OBJECTS OF THE INVENTION Accordingly, it is an object of this invention to provide a low cost, high efficiency and multi-adaptable device for controlling and regulating speed and direction of single-phase induction motors that overcomes the aforementioned deficiencies.

Further objects of this invention will become more apparent from a consideration of the drawings and ensuing description.

SUMMARY OF THE INVENTION

The above and other objects are achieved by a speed controllable single-phase motor including a split capacitor motor having a first, a second and a third terminal. A main winding is coupled between the first and the second terminals. An auxiliary winding is coupled between the second and the third terminals, wherein the split capacitor motor has its capacitor removed from the auxiliary winding.

The motor also includes a DC voltage supply comprised of a voltage multiplier having an output connected to the second terminal of the split capacitor motor, and at least one driving device including two switching elements connected to the DC voltage supply. One of the driving means and one of the two switching elements is connected to the first terminal of the motor and wherein one of the driving means and one of the switching elements is connected to the third terminal of the motor. The motor also includes a micro-controller performing an algorithm for generating one of a ninety degree (90°) and a variable phase-shift voltage between the main and the auxiliary windings. The micro-controller maintains frequencies and voltage amplitudes to direct operation of the motor.

In one embodiment, the motor also includes an asymmetric control unit comprising an output connected to the micro-controller, an additional speed control unit comprising an output connected to the micro-controller, and a current control unit comprising an output connected to the micro-controller.

BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention will be better understood when the Detailed Description of the Preferred Embodiments given below is considered in conjunction with the figures provided, wherein: FIGS. 1A-1D are schematic block diagrams for devices that control the speed of a single phase capacitor motor, as is known in the art;

FIGS. 2-7 are schematic block diagrams of a variable speed, single phase motor configured and operating in accordance with various embodiments of the present invention;

FIG. 8 depicts a period and duty cycle of a pulse width modulated signal of a preferred micro-controller;

FIG. 9 depicts a Sin function generated by a micro-controller, the microcontroller writing to RAM/FLASH Data Memory and then reading from memory; FIG. 10 is a schematic block diagram of a stand for PWM control estimation;

FIG. 11 illustrates graphically results obtained from the capacitor motor and converter of present invention;

FIG. 12 is a flowchart illustrates exemplary operation steps performed by the micro-controller of FIG. 10; FIG. 13 is a plot of torque versus current for a capacitor motor configured in accordance with the present invention;

FIG. 14 illustrates values of the voltage on the main windings for three exemplary embodiments depicted in FIGs. 1 A-1C, respectively;

FIG. 15 depicts values of phase shift between a main and an auxiliary winding;

FIGS. 16-18 depict results of measurements taken for capacitor motors including a converter configured and operating in accordance with the present invention; and

FIGS. 19-21 depict results of the mechanical, electromechanical and energetic measurements taken for capacitor motors including a converter configured and operating in accordance with the present invention. h these figures, like structures are assigned like reference numerals, but may not be referenced in the description for all figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2-4 are schematic block diagrams of variable speed, single-phase motors 100, 200 and 300, respectively, configured from split capacitor motors (with their capacitors replaced) and operating in accordance with the present invention, wherein converters drive the split capacitor motors for continuous speed, direction and torque control and regulations. FIGS. 2 and 3 illustrate embodiments of the inventive motors 100 and 200 wherein main (Lw) and auxiliary (Ls) motor windings have one common terminal. In FIG. 3, an electromotive force sensor 13 is included. FIG. 4 illustrates another embodiment where a variable speed motor 300 includes a division of the main and auxiliary windings.

As shown in FIGS. 2-4, a micro-controller 7 is connected to a power supply system, shown generally at 50, across a DC converter 1 and voltage multiplier 2, and to sensors of current 8, electromotive force 13, frequency setters 11, voltage 9 and voltage asymmetry 10. The micro-controller 7 generates and provides, across drivers 5, 6, 16 and 17 and switching elements 3, 4, 14 and 15, variable frequency voltages to main (Lw) and auxiliary (Ls) windings, according to mathematical dependencies (as described below). It should be appreciate that if the main and auxiliary windings are disconnected (e.g., not coupled to a common terminal), the voltage multiplier 2 may be eliminated from the circuit (e.g., as in FIG. 4). As described herein, the present invention eliminates the need for an external start/run capacitor and uses the additional winding of the single-phase AC motor for continuous speed, direction, torque control and regulation. The motor runs as a two- pase motor by means of the apparatus providing the generation of circular electromagnetic fields in the motor. FIG. 5 is a schematic electrical circuit diagram of the variable speed motor

(e.g., motors 100, 200 and 300). In FIG. 5 a voltage input, shown generally at 110, from, for example, a fixed-frequency AC utility power line, supplies power to the variable speed motor (e.g., motors 100, 200 and 300) across filter 20. In one embodiment, the voltage input 110 is comprised of either a 230V, 50Hz single phase, a 110V, 60Hz, or any other single-phase supply source. Two rectifiers receive the AC power input 110 and convert it into positive and negative DC voltages. In one embodiment, a first rectifier is comprised of diode 21 and a capacitor 22. The first rectifier supplies a positive DC voltage. A second rectifier is comprised of a diode 23 and a capacitor 24. The second rectifier supplies a negative DC voltage. As shown in FIG. 5, an inverter section, shown generally at 120, of the power supply 110 has four controllable switching devices 25-28. In one embodiment, the switching devices 25-28 are comprised of four insulated gate bipolar transistors (IGBT) each in parallel with a freewheeling diode. The first rectifier (e.g., diode 21 and capacitor 22) supplies a positive DC voltage to the power input for the first switching device 25 and the second switching device 26. The second rectifier (e.g., diode 23 and capacitor 24) supplies a negative DC voltage to the third and fourth switching devices 27 and 28, respectively. Pulse-width-modulated (PWM) signals from micro-controller 7 are supplied to the control input for each of the IGBT transistors 25-28. The PWM signals control the operation of each switching device 25-28. A pair of signals from drivers 29 and 30 supply each control voltage input of the IGBT transistors 25-28. The power outputs from switching devices 25-26 and 27- 28 are connected to the main and auxiliary windings of motor 19. The common terminal of motor 19 is connected to the DC voltage supply ith a voltage multiplier. A converter operation control mode is actualized by means of corresponding units 9- 12.

The unit 9 provides a minimum value of a starting voltage according to the motor's current. The unit 10 provides a tasking frequency signal that changes the smoothness. The unit 11 provides an alternative speed control rate. The unit 12 provides a voltage asymmetry signal between the main Lw and auxiliary Ls windings of the motor. The signals of these units are input by the micro-controller 7, which then supplies a voltage to the main Lw and auxiliary Ls windings. Selection of the operation mode is actualized by means of switches 25-28.

Control Algorithm.

The present invention comprises of a variable speed motor formed from a split capacitor motor with its capacitor replaced by means of driving the split capacitor motor. The driving means first provides a signal of a minimum value of voltage according to the motor's current. A second signal of voltage is asymmetry between the main and auxiliary windings of the motor, and a third signal of tasking frequency changes the smoothness. These signals are input by the micro-controller, which then forms a voltage of main and auxiliary windings. hi one aspect of the present invention, a frequency converter for the foregoing single-phase motors (e.g., motors 100, 200 and 300) performs in accordance with the following principles :

Um = F (/) < U_Dc Ua = Ca * Um Where: Um - voltage of the main winding Lw; Ua - voltage of the auxiliary winding Ls; Ca — coefficient of the asymmetry windings; U_DC - voltage of the direct current in the output of first and second rectifiers.

The main and auxiliary windings are both 90 degrees to the voltage.

In one preferred embodiment the driving means includes two switching elements, two drivers and the micro-controller for forming a tasking algorithm of speed control. Each of the two switching elements is connected to a DC voltage supply, and the output is then connected to a voltage multiplier. The common terminal of the main and auxiliary windings of the motor is connected to a special organized point in the output of the voltage multiplier. The other terminals, two and three of the main and auxiliary windings, are connected to a switching element accordingly. The law of the forming voltage is calculated by means of a micro-controller

(e.g., micro-controller 7) according to the parameters of the motor and Equation 1, as follows:

Where:

R - active resistance of a main winding Lw;

X - reactive resistance of a main winding Lw; and Realization of the principle of inductive motors

const does not provide a necessary electromagnetic torque of the motor.

If a frequency converter is actualized by the principle of inductive motors XJIf- const, a part of electromotive force is reduced relative to the supply voltage. A magnetic flux and electromagnetic torque of the motor is also reduced. By reducing frequency from about fifty Hertz (50Hz) to about twenty Hertz (20Hz), the maximum torque is reduced approximately four times. The control algorithm of the voltage as a function of frequency is actualized by means of a micro-controller with pulse width modulators. The control of IGBT transistors 25-28 of the motor (FIG.5) is achieved during each modulation time T {T ≤ 0,1 ms) . In each time T a present angle, is calculated in accordance with Equation 2, as follows:

Θ = θ₀ + 2π ∑ + 2π.m (2)

11=0

In one embodiment, the time of switches 25-28 operation mode is calculated in accordance with Equations 3-6, as follows:

=-(l + U*mSinθ) (3) π≥θ≥O

_-(l-U*m)Sinθ t₃ — 2 (4)

2π ≥ θ ≥ _Tx

π

≥Θ≥O (5)

2

3

Iπ v≥≥θθ≥≥— π

2 τ = --(l-U*a»Cosθ) (6)

3 _^ ._^ π where — 71 ≥σ≥ —

2 2

In one embodiment, the aforementioned equations are implemented as an algorithm within a PC-based micro-controller (e.g., model no. ADMC 300 from Analog Devices Ltd.) including software for variable speed AC induction motors. The controller board is very expensive for single-phase capacitor motors. Therefore, in another embodiment, a micro-controller (e.g., model no. ML4423 from Micro Linear Ltd.) was employed. The Micro Linear micro-controller, however, doesn't provide required parameters of a single-phase capacitor motor. Accordingly, in yet another embodiment, a micro-controller variant used in the frequency converter was sought. In the micro-controller variant embodiment, a microchip with a flash-memory and built in programmable mask ROM, e.g., a model PIC16F876 microchip of

Microchip Technology Incorporated (Mountain View, CA), is implemented.

In another embodiment, The micro-controller calculates a present angle of the control switches.

θ =6?₀ + 2 f₂π 2 +2π m (7) n=o where: fi - a task frequency f₂ - a modulating frequency

The time of switches operation mode is: t_lj2 = ± _r U*ι Sin θ (8) t_3>4 = + _T U*₂Cos θ (9)

The invention further comprises a method for forming a capacitor-less motor from a split capacitor type, motor by: removing the capacitor, connecting a sensor of current and electromagnetic power.

PEM = i + _a- , where (10)

• Electromotive force of motor windings

• Current of main and auxiliary windings • According to a value of P_EM micro-controller calculates an electromagnetic torque of motor (Tm) and forms a value of voltage in the function of a tasking frequency and Tm.

The invention additionally comprises a method for forming a variable motor from a split capacitor type motor by; removing the capacitor; disconnecting a main and auxiliary winding to another switching element; connecting a micro-controller to these switching elements separately and driving the motor via the controller in all ranges of the tasking speed. It is therefore, not required to regulate the DC voltage. The invention additionally comprises a method for forming a variable motor from a split capacitor type motor by; removing the capacitor; disconnecting a main and auxiliary winding to another switching element; connecting a micro-controller to these switching elements separately and driving the motor via the controller in all ranges of the tasking speed. It is therefore, not required to regulate the DC voltage.

The invention additionally comprises a method for foreseeing a variable motor from a split capacitor motor by connecting the main winding in parallel with the auxiliary winding and a start/run capacitor. Thereby the motor's windings are connected to one switching element (two transistors) instead of four or eight transistors. The microcontroller is connected to this switching element and drives the motor via the controller in the range 1:2 (from 0.5 to nominal speed of the motor).

In this range of speed regulation, this method provides essentially to improve the energetic parameters of the motor (power factor and efficiency). Thus it simplifies and reduces the price of the driving means. In cases where there is no need for full speed range regulation from nominal speed to low speed (for example, it needs only nominal speeds and speed of 0.5-0.7), this method provides switching of the motor windings from the converter device directly to the power supply network via the bypass elements.

This method is unique for speed regulation of split capacitor motors where it is impossible to disconnect the main and auxiliary windings that are shown in FIG. ID and FIG. 6.

Calculation of PWM parameters.

FIG. 8 depicts the period and duty cycle of PWM for the preferred microcontroller (e.g., Microchip Technology Incorportated's PIC16F876 microchip). As shown in FIG. 8, the PWM period is calculated (in accordance with Equations 13 and 14) by means of dependence:

PWM Period.

PWM period = [(PR2) + 1] • 4 • Tosc •

• (TMR2 pre-scale value) (13) Where:

= 20Khz

TMR2 prescale value = \;PWMperiod = 5 μS PR2 - parameter for an exemplary calculation, PR2 = ^ - 1 = 249, (14) Tosc

The number two hundred and forty-nine (249) is written to register PR2. As a result, fpwm=20Khz as shown in FIG. 8.

PWM Duty Cycle.

Equation 9 is used to calculate the PWM duty cycle.

PWM duty cycle = value₁₀ Bits • Tosc • TMR2 pre scale value

1 value lOBlts

= value₁₀B.ts ^# - 1 = focy 20.10 Hz

= value!0Bits • 50nS (15)

Equation 10 provides a maximum PWM resolution for a given PWM frequency (in bits).

Max. resolution =

bits ^:

Log{2)

Log2

Table 1 illustrates relational value₁₀Bιt — duty cycle.

Table 1.

In accordance with the present invention, the micro-controller estimates frequency generation for Sin# and Cos# by two methods.

1. Real time Sin function generation.

2π V = — — Y = Sini * l) - step one grade

360

If V is equal to 2π /360, and O ≤ i ≤ 360 , then frequency equal 1Hz

2π

More V, (for example V = )

36

More frequency and less accuracy of Sin(V*i) function - up to 40Hz.

2. Sin function generation, a micro-controller writing to RAM/FLASH Data Memory, and then reading from memory.

For example: if i = 72, then this method provides up to about 2Khz, Sinc frequency (see FIG. 9). In one embodiment, the Sin function generation method is preferred.

Function Dependences.

U- F_\ (oc ) - voltage function for speed potentiometer

T = — = p₂ (oc) - frequency function for speed potentiometer

oc ■ potentiometer position (0-31) Some perceived limitations.

1) Apparatus limitations:

• Memory and flash and RAM 256/368 bytes

• Frequency of oscillator of PICI6 - 20MHz • Bit resolution for ADC - 10 bit

• Bit resolution for PWM - 10 bit

2) Algorithm limitations:

• Interval for/in frequency conversion 3 - 60Hz

• Form for voltage function - linear/non-linear • PWM - on the base Sin/Cos functions

Preferred Methods for overriding limitations.

• Selection variables in program with 8bit

• Replacement operands *,1 (multiplication, division) with operands « - left shift,» - right shift

• The required functions are programmed to transform from an analogue to a digital form.

FIG. 10 is a schematic block diagram of a stand for PWM control estimation. In FIG. 10, components for program preliminary testing are illustrated. These components include, for example:

Speed Vmin

Analog inputs Ramp Time Asymm

Start

V/F profile

SW1 - digital input Start/ Stop Direction

LED 1 , LED2 - digital outputs J^" Run

Relay • Two analog filters for visual PWM form dependences

• Digital to analog converter (DAC) is for a direct frequency estimation (e.g., as described with reference to FIG. 9) • Digital display LCD is for digital output reflection results.

Table 2 illustrates results of U*_m = F(f), determined utilizing the micro-controller of FIG. 10. FIG. 11 illustrates the results graphically.

Table 2. FIG. 12 is a flow chart of an algorithm employed by the micro-controller of

FIG. 10.

Exemplary Testing of Capacitor Motors. Tests of capacitor motors including regulated driving gear-based frequency converters, constructed and operating in accordance with the present invention, were carried out on loaded test stands in a laboratory and in commercial environments, hi some of the tests, a supply voltage was provided at 60Hz. The frequency converters of the present invention were also employed with a number of motors and blowers of air conditioning and fan devices having, for example, differing supply voltage and operating conditions, e.g., a York Ltd. (Oklahoma) and A.O. Smith (Ohio) devices at a 115V supply. International supplies were tested by testing a Germany blower device and an Ol o (Romania) fan having a supply of 230V.

In performing the exemplary testing, the inventors determined: (1) mechanical and electromechanical characteristics of several types of single-phase capacitor motors that are compatible with the functionality of the inventive frequency converter system; (2) active parameters of the electric drive including the motor-frequency converter; (3) a preferred heat mode for the motor's operation; (4) exemplary and prospective applications of the controlled speed electric driver (e.g., single-phase capacitor motor frequency converter) in air conditioners of various companies and in the drives of fans, compressors and other mechanisms.

Test Procedures.

For the testing of motors of types 301-709, 31-945 (MOER 718/4D), (Power 250W), 31-640-1 (power 375W), 31-848 (power 250W), nominal axle load's varying values have been taken with an auxiliary (starting) winding of the motor that was connected to the power supply network (230V) through one capacitor. Three main windings of motors 31-709, 3-945, 31-848 were in a connected series that allows for three different values of rotational speed (e.g., FIGs. 1A-1D). Motors 31-640 and MOER 718/4D are without additional main windings for speed regulation. The synchronous rotational speed of the motors types 31-709 and 31-945 equals 1,000 rpm while the motors 31-848, 31-640 and MOER 718/4D equals l,500rpm.

The additional windings are in a connected series to the main winding in the standard scheme of motors, 31-709, 31-945 and 31-848. They are not used when motors are connected through the frequency converter. Also, the capacitor that is usually connected to the series with the auxiliary winding is excluded (e.g., FIGs. ID and 4)

A magnetic particle clutch, which is a friction device, is used with a special controller of Lenze Ltd., type 14 512-01 since the load for the tested motors has already been used. For torque transmission, a friction connection between bearing mounted stator and rotor is obtained. Due to the special magnetic particles located in the air gap between the stator and rotor, bearing arrangements separate both. The primary component is also the coil carrier stator and can be supplied from the DC by slip rings or fixed connections. The electrical connection of the breaks is carried out by means of a spade plug and socket installed in the face of the stator. The amount of torque transmitted is directly proportional to the exiting current the torque transmits via the current flowing in the coil. Torque depending on current is shown in FIG. 13.

For measuring a testing motor torque, a special operator panel and PLC unitronics M90 that received information from a current sensor, was employed. An operator panel for measuring the motor speed was also employed. The test included a pulse sensor of the type Balluff BES516-366-BO-C and photo-contact tachometer of the type DT 2236 for a speed sensor.

A PCB mounting Hall effect is used for measuring a voltage end current in the motor windings. Transducers type LTA 50P/SP1 and LV 25-P are used. The current Hall sensors provide a possibility of measuring a phase angle between the main and auxiliary windings' current. These tests are carried out by means of an oscilloscope.

In one test a capacitor motor having a frequency converter system constructed and operating in accordance with the present invention, was evaluated on a dynamometric stand of the Magtrol, Inc. in Redmond Amcor Ltd. The test stand includes a dynamometer (model 4619), a power analyzer (e.g., ampermeter, voltmeter, wattmeter) model 4612, computing indicator (power, torque, speed - model 4615, x-y recorder, type 3086, torque-speed multiplier and output control- model 4625).

In addition to testing on the dynamometric stands, the electric drive has been tested on fans and air conditioners (in regular service conditions) produced by, for example, Tadiran Ltd. and Electra Ltd.

Tests on the state of the heat in the motors have also been conducted on air conditioners over several hours. The temperature of the windings has been calculated by the method of resistors before and after the functioning of the drive. The temperature of the motor's body has been measured by means of a thermometer

APPA51.

The voltages on the auxiliary winding and the capacitor have been measured with and without additional windings, in standard connection schemes for the capacitor motor. The profile of change in the values of the voltage is shown in FIG. 14.

The value of the phase shift between the main and auxiliary windings has been measured, in laboratory testing of the motor 31-709, through the standard scheme, as well as through the frequency converter. Results of the measurements are shown in FIG. 15.

The values of the voltage from the main and auxiliary windings of the electric motors are not controlled through the frequency converter. They are set, automatically fixed and equal in relation to the dependence U(f). The adjustment is carried out at the point of V_rain(F_mi_n), where the value of the consumed current is minimal. In the controlled zone of the frequency (the rated value above), the voltage has remained in relation to the nominal voltage and is not controlled.

Results of the measurements taken for capacitor motors including the inventive converter are shown in the Tables 3-10 and diagrams FIGs. 14 - 21.

Table 3

Table 5

The mechanical and electromechanical parameters of the motor 31-709 run with the present invention's frequency converter (without an additional capacitor).

Table 6: The output frequency is 60Hz.

Table 8: The output frequency is 40Hz

Table 9: The output frequency is 30Hz

Mechanical electromechanical and energetic parameters of motors types 31- 709, 31-848, 31-945 tested on the dynamometric stand of Redmond-Amcor are in Table 11 and FIGs. 19-21.

The mechanical and electromechanical parameters of the single-phase capacitor motor 31-709 in standard sentences with additional capacitor 8 μF are found in the following: Table 3. - one main and auxiliary winding (as shown in FIG. 1A); Table 4. - one additional winding (as shown in FIG. IB); and Table 5. - two additional windings (as shown in FIG. 1C). Observed Results.

The following results have been obtained from the aforementioned test processes.

As shown in FIG. 14, the value of the voltage on the main windings is substantially higher in standard connection schemes for the tested capacitor motors than that on the auxiliary winding. As a result, the connection of the special frequency converter with the electric motor, in certain cases, does not provide a necessary controlled voltage range on the auxiliary windings.

A comparison of two embodiments of the present invention (illustrated in FIGs. 2 and 3), shows it is possible to receive the same energetic parameters of the systems. Although in the system with a standard connection of motor windings, it is necessary to double a voltage in a DC link.

Using a frequency converter with extra voltage is insufficient for the tested motor and leads to the decrease in the mechanical operating speed at the rate of 50Hz. In some cases, the extension of the controUed-frequency range over the rated frequency proves to be sufficient for maintenance of the high unit performance (motors 31-709 and 31-604). The maximum necessary frequency is 56Hz-60Hz. for the motors, types 31-848 and 31-945, the mechanical operating speed is secured only by the torque values close to the critical values of the motor torque. The extension of the controUed-frequency range over the rated frequency is insufficient. The necessary effect is achieved as a result of the reduction of the nominal voltage of the windings from 230V to 190V. (FIGs. 19 and 20).

Results of the capacitor motor having an inventive frequency motor converter, developed without optimization of its parameters, provide an increase in the drive efficiency by at least ten percent (10%) in the entire controlled- velocity range. It subsequently results in the reduction of heat loss in the motor, for example, Table 11.

The frequency control of the serial single-phase capacitor motor allows for a significant extension of the controlled speed range to 1:5-1:6 depending on the type of the mechanism. Rigidity of the controlled mechanical characteristics is also lower than the rigidity of the natural characteristics of the motor.

Some Conclusions drawn from the Testing.

The use of the frequency converter even with the serial motors that are non- optimized for the frequency control opens wide prospects for applications of the drive for air conditioners. Additionally, it substantially reduces the range of produced motors and decreases the production expenses resulting from the exclusion of additional windings, start-up capacitors etc.

Additional Considerations.

Optional Features include:

1. A frequency converter embedded into existing constructions of air conditioners and minimizing expenses on its casing.

2. Digital input subsystems on the base of PIC18F2431 or PIC18F4431, LCD and keyboard.

3. Integrate functions of direct digital control of the motor with control functions of air conditioners.

4. A two-phase motor with the circular field in the entire controlled-speed range and the range of load torque values. Together with the frequency converter, it causes a sufficient increase in the efficiency and the power drive.

5. Robust design integration of the converter and motor.

6. A single-phase motor with converters for introduction into other sectors of the market (e.g., employed within machine and robot drives).

While the present invention has been described and illustrated in connection with preferred embodiments of a frequency converter for use with capacitor motors, many variations and modifications, as will be evident to those skilled in this art, may be made without departing from the spirit and scope of the invention.

The invention is thus not to be limited to the precise details of methodology or construction set forth above as such variations and modification are intended to be included within the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A speed controllable single-phase motor characterized by: a split capacitor motor (100, 200) having a first (1), a second (2) and a third (3) terminal, a main winding (Lw) coupled between said first and said second terminals, an auxiliary winding (Ls) coupled between said second and said third terminals, wherein said split capacitor motor has its capacitor removed from said auxiliary winding; a DC voltage supply (1) comprised of a voltage multiplier (2) having an output connected to said second terminal of said split capacitor motor; at least one driving means (5, 6) comprising two switching elements (3, 4) connected to said DC voltage supply wherein one of said driving means and one of said two switching elements is connected to the said first terminal of said motor and wherein one of said driving means and one of said switching elements is connected to said third terminal of said motor; a micro-controller (7) performing an algorithm for generating one of a ninety degree and a variable phase-shift voltage between said main and said auxiliary windings, said micro-controller maintaining frequencies and voltage amplitudes to direct operation of said motor; an asymmetric control unit (10) comprising an output connected to said microcontroller; an additional speed control unit (11) comprising an output connected to the micro-controller; and a current control unit (9) comprising an output connected to the micro- controller.

2. The speed controllable single-phase motor of claim 1 characterized in that said driving means further comprises: sensors of current phase control (8) of said main and said auxiliary windings; and sensors of said motor's electromotive force (13), said electromotive force sensors having an output connected to said micro-controller forming mathematical dependencies of said motor's electromagnetic torque.

3. The speed controllable single-phase motor of claim 1 characterized by additional control units for changing one of directions of rotation (clockwise, counterclockwise, forward and reverse), and soft start and stop, dynamic braking, and torque boost.

4. A speed controllable single phase motor characterized by: a split capacitor motor (300) having a first (1), second (2), third (3) and fourth

(4) terminal, a main winding (Lw) between said first and second terminals, an auxiliary winding (Ls) between said third and fourth terminals, wherein said split capacitor motor has its capacitor removed from between said third and forth terminals; a DC voltage supply (1); a driving means comprising: four switching elements (3, 4, 14, 15) each of said switching elements connected to said DC voltage and each of said switching elements connected to a single one of said terminals; four drivers (5, 6, 16, 17) each of said drivers connected to a single one of said terminals; a micro-controller (7) connected to said single phase motor; an asymmetric control unit (10) having an output connected to said micro-controller; an additional speed control unit (11) connected to said microcontroller; and a current control unit (9) have an output connected to said microcontroller.

5. The speed controllable single-phase motor of claim 4 characterized in that said driving means comprises sensors from said current phase control (8) of the main and said auxiliary windings and sensors of said motor's electromotive force (13) having an output connected to said micro-controller that forms mathematical dependencies of the motor's electromagnetic torque.

6. A speed controllable single-phase motor characterized by: a split capacitor motor (100, 200, 300) containing one of a first (1), second (2) and third (3) terminal and a first (1), second (2), third (3) and fourth (4) tenninal; a main winding (Lw) between said first and said second terminals; an auxiliary winding (Ls) between one of said second and said third terminals, said second and third terminals, and forth and first terminals; a start/run capacitor between one of said third and first terminals and between said third and forth terminals; a DC voltage supply (1) comprised of a voltage multiplier (2) having a center tape output connected to said second terminal of said motor; driving means (5, 6) comprising one switching element (3, 4) connected to said DC voltage supply and to the said first terminal of said motor; and a microcontroller (7) using an algorithm to generate frequencies and voltage amplitudes to ensure proper operation of said motor.

7. The speed controllable single-phase motor of claim 6 characterized in that said driving means (5, 6) comprises two switching elements (3, 4) connected to said DC voltage supply and to said first terminal of said motor via said other switching element that is also used for a connection, wherein said first terminal of said motor is connected directly to said supply voltage and provides a bypass option to said inverter.