JPS586091A - Device for controlling supply of power to ac induction motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention generally relates to a rounding device for controlling a transducer;
In particular, it relates to an energy saving controller which controllably varies the average voltage supplied to the motor as the motor load changes.

In the discussion of the prior art, there is increasing emphasis on saving electrical energy in the design of motors and their applications. In order to match the operating efficiency of such electric motors to the water spraying required for wiping, a variety of increasingly complex control systems have become available, e.g., from U.S. Pat. No. specification and NASA (
辅8A) Rehoto No. NFS-λ3 Kogo describes a control circuit that reduces the power loss of an AC induction motor by detecting the power factor, that is, the phase delay between the voltage and current of the motor. . This information is used to vary the average voltage supplied to the motor to maintain a constant optimum power factor in the face of varying loads and line voltages.

The improver of the above-mentioned U.S. Patent No. 1Aos,
This has expanded the useful applications of basic power factor control circuits in a variety of ways and increased the range of protection for electric motors controlled by such circuits. Other desired additional functions include an inrush current limiting function, an overcurrent tripping function, a start-up control function, and an open phase detection function. Under extreme conditions such as extremely high load conditions and severe load transients, motor controllers that operate by sensing power factor changes may not perform satisfactorily or even shut down the motor. In addition, stability problems sometimes occur with power factor motor controllers under special load conditions that may cause the power factor motor controller to become unstable. To minimize such stability problems, most power factor magnetic motor controllers are designed to have somewhat limited response times.

It would be desirable to provide a controller that exhibits stable performance over a wider operating range and that responds quickly (to load transients).

In some industrial environments, higher than normal line voltage conditions often exist. With such high voltage
Operating an electric motor consumes more energy than is necessary to properly drive the load. get high'
It would be desirable to provide a motor controller that reduces the energy consumed by the motor under voltage conditions.

Applications such as in mining and construction may result in overhauling or regeneration load conditions. This occurs, for example, when the crane is underweight and the load attempts to drive the motor at a faster speed than the synchronous speed. The power factor controller 2 will sometimes operate the motor in an undesirable manner under such conditions; therefore, the power factor controller 2 will operate the motor in such a way that the benefit of an overhaul load is actually obtained to save energy by returning power to the mains. It is desirable to provide a controller that operates the

Finally, although power factor controllers generally provide satisfactory service in many applications, it would be desirable to provide equal or improved performance in a simpler device.

DISCLOSURE OF THE INVENTION The present invention, in its broadest form, provides slip detection means for detecting slip in an AC induction motor and generating a slip signal indicative of the slip, and a reference signal for adjusting the motor to a desired operating state. a reference means for generating an alternating current; a feedback means connected to the slip detection means and the reference means for comparing the slip signal and the reference signal and generating a feedback control signal representing a difference therebetween; connected in series with said '1lilc#Ib machine under power supply and control for varying the average voltage supplied to said motor, and connected to said feedback means for establishing a desired operating state of said motor; and control means for controlling an average voltage supplied to the motor in response to the feedback control signal.

According to a preferred embodiment of the invention, an apparatus for controlling an AC induction motor is provided.

This device includes detection means for detecting a slip in the motor being controlled and generating a slip signal representative of this slip, in which a reference signal corresponding to the desired operating condition 1IIK of the motor is generated. The slip signal and the reference signal are supplied to feedback means connected to the sensing means and the reference signal generating means. The feedback means compares the slip signal and the reference signal and generates a feedback control signal representative of the difference therebetween. This feedback control signal is connected in series with the motor and AC power supply.
A control means such as an anti-parallel BOR connected in C is supplied. The feedback control signal actuates the control means to vary the average voltage supplied to the motor to establish the desired operating conditions of the motor.

The present invention further comprises means for detecting 1IlcfL flowing through the motor and for generating a current signal that is combined with the slip signal and the reference signal and supplied to the feedback means to generate the feedback control signal. The implementation of filK provides further advantages. As the motor slips or the current drawn by the motor kfi decreases, each of which reduces the average voltage supplied to the motor, thereby producing a feedback control signal that reduces the energy consumed in the electric wJ machine in these conditions M&C. incorporated to supply.

The slip of the motor is determined by measuring the voltage appearing across the control means, rectifying this voltage and integrating it to provide a DC slip signal.

As described herein, the illustrated apparatus is used to control a J-phase change tIL-conduction motor, each phase containing 80R connected in anti-parallel, the voltage across each SCX pair being integrated. , are averaged and combined into the slip signal. Additionally, an R transformer is provided for each phase of the motor, and the output of each current transformer is rectified and combined into a DC current signal. The slip and current signals are combined with a reference value to generate a feedback control signal that is provided to drive a gate firing circuit connected to each 8OR gate electrode. The gate ignition circuit may be configured, for example, according to the teachings of the above-mentioned US Citizenship Permit No. θj1 Ken 1.

In another embodiment of the invention, a DC line reference control signal is provided that is proportional to the fin voltage of the power supply. The DC voltage derived from the voltage across 80R of each phase of the motor is subtracted from the line reference control signal derived from the AC line voltage to obtain a slip signal.

An apparatus constructed in accordance with the principles of the present invention can accurately control an AC motor without shutting it down, even when severe no-load to full-load transients occur. Even when loads become extremely large, such devices continue to exhibit excellent performance. Moreover, the regenerative load applied to the electric motor controlled by such a device allows the electric machine to operate properly without returning power to the AC power source.

For a detailed understanding of the invention, reference is made to the following description of a preferred embodiment, shown by way of example in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described herein, the present apparatus provides an improved energy saving controller for use with AC induction motors by sensing motor slippage and generating a signal corresponding to the value thereof. This slip signal is compared with a reference voltage and the resulting comparison signal is used to
The average voltage applied to the beam is varied, thereby maintaining the motor at a relatively constant slip speed.

FIG. 1 is a graph showing motor slip speed as a function of motor load and motor voltage. A controller incorporating the principles of the present invention can be used to establish the nine driving curves shown in FIG. In Figure 1, the voltage applied to KanwJ is 100 - 1o at load.
The motor voltage can be changed from o-motor voltage to approximately υ the motor voltage when the iIlcwJ peak is in a no-load state. It can be seen that the slip speed of the motor varies slightly from about s% to about 3-. The lowest voltage at the unloaded gland is determined by setting a reference voltage, as explained in more detail below. The variation of the voltage as a function of the motorized load when controlled by a device incorporating the present invention is shown in FIG.

The second drawing is a simplified circuit diagram of a J-phase **IIE motor operated by a motor controller incorporating the inventive mass. J-tei's sojinta A, B, and C are J-a
The pillow δ is inserted into the clear winding of the electric motor SO. What is connected directly to each side is 91 pairs of 7 recon systems connected in antiparallel! & Ruhonko (SOR) Hiroko-Daku.

The gate electrode 10 of each SOR is inserted into the gauge point a circuit lIo. This gate ignition circuit da0 is connected to the electric motor SO
Gate drive pulses'' are applied to the SOR at appropriate times to vary the average voltage applied to each phase of the SOR in a well-known manner.

As is well known to those skilled in the art, the average voltage supplied to each phase of motor 5Q can be controlled by varying the duty cycle of 80R4'λ~q7. Electric motor! In order to apply the full line voltage to each phase of
The AC waveform is activated by the AC waveform and conducts throughout the entire 34°0° range. By correspondingly reducing the duty cycle of the SOR in such a way that the SOR conducts for only a portion of the AC twin voltage cycle, the average voltage can be lowered. The voltage waveforms appearing on the seven phases of motor so are shown at 12 in FIG. Phase O 5OR4
1A and F? The voltage waveform appearing across vs is proportional to the slip speed of the motor. As can be seen from the symbol /j in FIG. 3, a high slip value for the motor SO causes a high voltage vs.

The voltage vs#'i is applied to the transformer W/, where it is reduced to a level suitable for processing by the logic circuit and rectified by the diode bridge /1, labeled /j in FIG.
Form a series of DC pulses as shown in a. These pulses are applied to the negative input terminal of the amplifier M1, and the positive input terminal of the S amplifier A/ can be connected to a line reference circuit CO1, which is supplied with the line voltage V. The rectified voltage pulse /ja, which constitutes the intermediate signal, is integrated by the amplifier A/ and subtracted from the line reference signal of the line reference circuit-l. Amplifier A/ inverts the signal obtained and supplies the appropriate signal to node J. The motor voltage regulating circuit 1 supplies a reference signal to the connection point 3 through the potentiometer it. The current feedback signal is a variable current diode, an amplifier A, and a potentiometer! and diode J/'
It is supplied to the connection point Ko3 through r. The output of the amplifier module is adjusted by a potentiometer to set the highest motor voltage delivered under full motor load conditions. This may not be the same as the line voltage, as electric @SO may be too high for some applications, and may operate more efficiently at a reduced voltage, thus saving extra energy. It is from.

The voltage supplied from the motor voltage regulation circuit 1 is applied to the connection point KOJ with the same polarity as the motor current signal from the amplifier MUCO. Whenever the motor is under virtually no load, the potentiometer! Adjust the motor voltage to the lowest voltage.

The output of the feedback amplifier circuit aO is a positive analog DC voltage used as a signal input for the gate firing circuit aO; the higher this voltage is, the longer the duct is turned on, and The average voltage supplied to the electric mjo also becomes higher.

A multiplier A/1 is also used to filter the feedback voltage so that a low ripple voltage is supplied to the feedback amplifier circuit -0 and hence to the gate firing circuit DA0. The cut-off frequency and response time of the filter are chosen to provide the desired stability for all operating conditions of the motor jθ.

Although the current feedback signal provided by amplifier A- is not necessary for operation of embodiments of the invention, its use allows greater stability and operating range of motor SO.

FIG. v is a block diagram of a motor controller employing the principles of the present invention utilizing a J-phase detection and motor protection circuit arrangement. J-phase circuits that perform virtually the same function as the single-phase circuit of FIG. 3 are designated by the same reference numerals with the suffix @am added.

The motor S0 shown in FIG.
There is no need to connect the logical ground to the neutral conductor of a wye-wired motor for proper operation, and therefore there is no need to connect the neutral conductor of such a motor to the logical ground or both to ground. , each phase winding is connected to the appropriate front phase of the three-phase line via a pair of anti-parallel 8CRs.

Each gate electrode of the SORs λ to q7 is controlled by a gate ignition circuit θ as shown in FIG. The loads 1III of each SOR pair are indicated by A'B'C' and are connected to the slip detection circuit /Ja. This slip detection circuit /Ja is also connected to the line of each SOR pair, thereby detecting the Ot pressure v8 between both ends of each SOR pair. This J-phase signal is rectified, filtered, and conditioned to provide a DC signal representative of motor slip. A life M subcircuit/IL is also connected to the line side of each SOR pair. The line reference circuit JJ supplies a direct f/! line voltage reference signal to the slip (no. 4 generating circuit 3J). A slip feedback signal is generated by subtracting the 1d signal generated by JIL.

This slip feedback signal is supplied to the feedback amplifier circuit -0 through the connection point -3. The motor voltage node reference signal generated by the motor voltage regulating circuit ', lλ is also supplied to the feedback amplifier circuit -0. The status signal input to the Ml feedback amplifier circuit θ can be supplied by combining the slip feedback signal and the output of the J-phase current detection circuit/A. i[
The current sensing circuit 6 is connected to a current transformer S coupled to the load side conductors A', B' and C'. Of course, the current transformer can also be connected to the line side.

A feedback control signal is supplied to the gate firing circuit lIO through the feedback amplifier circuit 20d connection point J0. Electric motor! The no-load operating voltage of fo is determined by a potentiometer/1ftvI! that changes the value of the motor voltage regulation reference signal supplied by the motor voltage regulation circuit Coco to the feedback amplifier circuit CoO. Section A is selected. The highest voltage supplied by the controller during heavy load conditions of the motor is determined by the potentiometer 2? connected to the current sensing circuit ib7. is selected by adjusting.

Therefore, an average voltage of 0 is supplied to the X motor θ by the SOR during heavy load conditions. When the motor is under no load, motor jθ slips and this FL'Wc
The currents drawn therefore both tend to decrease. The change in slip is manifest itself as a change in the voltage v8 across each SOR pair; this voltage change is sensed by the slip detection circuit /Ja and reduces the voltage supplied to the slip signal generation circuit 33. This increases the slip feedback signal supplied to node=3 by the slip signal generating circuit 3J. Similarly, the reduced current flowing through the motor windings is reduced through the current transformer! This information will be sensed by the current sensing circuit/4. A signal greater than 1 will therefore be provided to the feedback amplifier circuit Q through node 3, which provides a larger feedback control signal to the gate firing circuit DA0 through node 3θ. In response to this change in the feedback control signal, the gate firing circuit UO generates a pattern of firing pulses consisting of BCR'l-~
EiCR reduces the proportion of AC line voltage that EiCR conducts, thereby reducing the
By lowering the average voltage supplied to the 0 block, the amount of energy used by the electric motor jO during light load conditions is reduced.

A number of additional operating and maintenance features are provided by the controller shown in Figure 1. For example, during motor start-up, the current drawn by the motor soK is several times greater than the normal full load current, which means that: Not only does this have the well-known undesirable effect of momentarily reducing the voltage supplying the electric motor, but it can also significantly increase energy costs by triggering high demand charges often imposed by utility companies. It can be. Current limiting circuit 31I effectively reduces the amount of incoming current lost caused by motor starting and provides a cutback signal to node J, which cutback signal is combined with various other signals and transmitted through node 30. It serves as an additional input to the gate firing circuit 4IO.

Current limiting circuit 3 is also connected to current trip circuit J1, which detects the occurrence of a severe overload condition that could damage the windings of motor 50. Upon detecting such a condition, the current trip circuit 34 generates an instantaneous trip signal which causes the gate ignition circuit H0 to immediately de-energize the motor 30 through connection point 3 and JO. In less severe overload conditions, the current trip circuit 36 can supply a timed trip signal to the start-open circuit λg, which likewise begins to shut down the motor jO, but only after a predetermined delay. be. When the current required drawn by the motor 50 is typically greater than the standard full-load operating current, the start open circuit I detects the motor start-up and effectively activates the timed trip function of the current trip circuit J6. Use it as a priest. Power supply unit-1 is provided for generating the control power necessary to operate the circuitry of the controller.

The open phase detection circuit is connected to phase conductors A, B and 0 on the line side.
If any one of these phases fails, it is detected and a signal is supplied through the connection point 30 to the gate ignition circuit DA0, thereby instantaneously stopping the motor 30.

The various parts of the controller shown in Fig.
! , a power supply device Koda, an open phase detection circuit 24, and a gate ignition circuit 4IQ.

FIG. 5 is a circuit diagram of the slip detection circuit/Ja, the line reference circuit/IL1 slip signal generation circuit 33, and the current detection circuit/A. The slip detection circuit/ja is
Each SCR pair 1IJ-I corresponding to phase, B, and CK respectively
I3. IIf-FA- is connected between both sides of 114-417. The line side conductor and load side conductor of each phase input are amplifiers /IIJ, /#j, corresponding to phases A, B, and O.
It is connected to the negative terminal and positive terminal of /lI, respectively, via an insulation resistor.

Each amplifier/113. /e! , /Hirohi and its associated enclosure perform the function of the transformer of FIG. 3 and are less expensive. The positive and negative power supply conductors are the same for each amplifier, but only the power supply conductors for the amplifier 181'IS are shown in FIG.
f, /dac to set its gain appropriately. Amplification 41741.7゜iII! r and /4
The output of I7 is applied to diode mud 171 y, s /, which rectifies the voltage pulses generated by the amplifier and applies these pulses to amplifier j3. The output side of the amplifier SS is connected to a slip signal generation circuit 33 via a resistor jj. The gain of the amplifier 3J is set by a resistor 3D. Resistor S4 and capacitor st are provided to reduce voltage spikes and provide a cleaner waveform.

The line voltage reference signal is provided by line reference circuit J/IL. Phase conductors A, B and 0 on the line side are transformers! Diode 1'j? and supply a pulsating DC voltage proportional to the voltage appearing on the phase conductors B and cVc.

When this voltage is supplied to the slip signal generation circuit 33,
It is applied to the positive input terminal of a voltage divider 6j, rectified by a diode 6o, filtered by a capacitor O7 and divided by a voltage divider consisting of a lattice resistor 4/and 6J. Amplifier 6j is supplied by line reference circuit aFc and outputs a line voltage reference signal to slip detection circuit l.
The signal provided by Ja is subtracted to generate a slip feedback signal at its output terminal. This slip feedback signal is filtered and conditioned by resistors 67.6 and 7.7. The slip feedback signal is then supplied to the feedback amplifier circuit-0 through the diode I.

A current sensing circuit 14 is also shown in FIG.

The signal from the current transformer to the current sensing circuit 14 is rectified by a diode and then combined and conditioned by an amplifier. A group of resistors t/ is provided to adjust the gain of the amplifier t to accommodate variations in current transformer tolerances and motor horsepower. The resistor 1/ is switched in to obtain the same voltage at the output terminals of the amplifier for different motor horsepower at 100-load. The output of amplifier 7 is applied through resistors EJ and 12 to the negative input terminal of amplifier 7, which filters and conditions the current feedback signal and also reverses the sensing of the current feedback signal as described below. do.

That is, when the motor current increases, the current feedback signal to the feedback amplifier circuit causes the gate ignition circuit to increase the detent cycle of the furnace.
Increase the average voltage supplied to the 0 winding. at the same time,
The increase in the slip of the motor SO is detected by the slip detection circuit/JlL, and the signal generated by this slip detection circuit/J1 is supplied through the slip signal generation circuit JJ, the feedback amplifier circuit -〇, and the gate firing circuit qo. The average voltage applied to the windings of motor 30 is increased.

The rising line voltage on phase conductors M, B and 0 is detected by the line reference circuit CO/IL.

This affects the slip signal generation circuit JJIC to generate a slip feedback signal which passes through the feedback amplifier circuit 0 and the gate ignition circuit POPs motor g.

The average voltage applied to IIklII of . Therefore, a high line voltage condition will not cause a corresponding increase in the average voltage applied to the motor jO, and the efficiency of the motor will be reduced by a controller that does not incorporate the principles of the present invention! is increased compared to the operation of O.

The current feedback signal from the current detection circuit/A and the slip feedback signal from the slip signal generation circuit 33 are combined at the connection point CJ and then input to the feedback amplifier circuit Q (the details of which are shown in FIG. 6). Ru. As can be understood from Figure 4, 1
The feedback control signal from node J is supplied to the negative input terminal of amplifier 19. This negative input terminal is connected to the power supply
A nine motor voltage adjustment reference signal derived from the regulated DC voltage provided by (FIG. 7) is also provided. This motor voltage regulation reference signal is adjusted with potentiometer /1 to establish the lowest average voltage to be supplied to the stateless motor jO when the motor is unloaded. The resistor OJ sets the gain of the amplifier it, but the resistor OJ and capacitor OJ
p forms a phase advance circuit for compensating for the delay caused by the time constant of the motor. Capacitor OSIIi approximately 40
Form a low pass filter set to the cutoff frequency of the HIM. Positive input terminal resistance of amplifier 9 -〇4
is connected to logical instructions via.

Is the output of amplifier g9 a resistor? / through gate ignition circuit q
It is input to θ. If the load on motor SO is increased, the value supplied to the negative input terminal of amplifier S9 (the combined value of the slip feedback signal, current feedback signal and motor voltage reference signal) decreases and This will cause the ignition circuit UO to output a larger output.

This will increase conduction through the 5ORF code. The average voltage supplied to the motor therefore increases. At the same time, if the load on the electric motor mho decreases, the value supplied to the negative input terminal of the amplifier 11 will increase, so that the electric motor! Reduce the average voltage supplied to O.

Effects of the Invention The electric motor controller according to the above-described embodiments of the invention considerably improves performance compared to conventional devices. Specifically, the motor can be operated satisfactorily over a wider range of motor load fluctuations without stopping. Responds more quickly to motor load transients than conventional coit rollers. If the inertia of the motor load is small, the illustrated embodiment provides a fairly stable controller. Additionally, a controller constructed in accordance with the principles of the present invention is suitable for regenerative load conditions or overhauling where the motor load attempts to drive the motor at a speed greater than the synchronous speed.
operating the motor properly during load conditions. During these conditions, the electric motor controlled by the device described above can actually supply energy to the power supply.

1 current detection circuit/when an overhauling load is present
4 (FIG. 9) supplies a voltage higher than the slip feedback signal from the slip signal generating circuit 33 to the feedback amplifier circuit θ to generate a larger feedback control signal from the feedback amplifier circuit 2Q.

This turns on the gate firing circuits θi/CBCjR4t, energizing current back to these 5ORIC lines. The greater the overhauling force, the more the 5ORId turns on until all of the 5ORId are turned on, effectively forcing all the energy and current in the stop to be returned to the line.

Finally, it saves more energy than traditional controllers because the motor can be operated at lower voltages under no-load conditions and also consumes less energy in the motor during full-load operation under high line voltage conditions. Therefore, the present invention provides a motor controller that exhibits significant advantages over prior art devices.

[Brief explanation of the drawing]

FIG. 1 is a graphical representation of a family of curves showing slip speed as a function of motor load for various motor voltages;
IJ is a partial block diagram of a device incorporating the principles of this invention. The circuit diagram shown in No. afjJ is a block diagram of a three-phase motor controller incorporating the principles of the present invention, No. ! The figure shows the slip detection circuit shown in Fig.
FIG. 6 is a circuit diagram of the slip signal generation circuit, line reference circuit and current detection circuit, and FIG. 9 is a circuit diagram of the fcf@return amplifier circuit shown in FIG. 5Q is electric motor, lJ& is slip detection circuit, co/a#'
i-line reference circuit, 3J is slip signal generation circuit, 20
is a feedback amplifier circuit, 4Iold gate ignition circuit, Vλ to 7 are F3CR, /'IJ, 1HiroI and /4I7 are amplifiers. m-1゜Patent Applicant's Representative Zeng Wa Do Teru - Niden Chia,
q branch li) i phrase (%) 1 moving box/load C association)

Claims (1)

[Scope of Claims] l Round slip detection means for detecting slip in the AC induction motor and generating a slip signal representing this slip; and for generating a reference signal corresponding to a desired operating state of the electric 11J machine. a reference means connected to the slip detection means and the reference means;
feedback means for comparing the slip signal and the reference signal to generate a feedback control signal representing a difference therebetween; and an average voltage connected in series with an AC power supply and the motor being controlled and supplied to the motor. and a control connected to said feedback means for controlling the average voltage supplied to said electric machine in response to said feedback control signal to establish a desired operating state of said electric machine. 9. A device for controlling the supply of electric power to an AC induction motor, comprising: means; 8. Apparatus according to claim 7, wherein the y-slip sensing means includes voltage responsive means connected to the control means for deriving an intermediate signal representative of the voltage appearing across the control means. 3. The slip detection means includes means connected to an AC power supply that is feeding the electric motor to supply an average DC voltage representing the AC voltage of the AC power supply, and detects a slip by subtracting an intermediate signal from the average DC voltage. Apparatus according to claim 1 for generating a signal. 4. The device according to claim 3, wherein the control means includes a pair of silicon-controlled rectifying elements connected in antiparallel. further comprising current means connected to the feedback means for sensing the current flowing through the motor and generating a current signal representative of this current, said feedback means increasing the average voltage applied to said motor as the predistribution current increases; 2. The apparatus of claim 1, wherein said current signal is incorporated into a feedback control signal to increase the current signal.