JP4598776B2 - Induction motor control system - Google Patents

Description

Detailed Description of the Invention

This application claims priority from Brazilian Patent No. P10305338-5 filed Nov. 28, 2003, and is hereby incorporated by reference.
[Field of the Invention]
This invention relates to induction motor control systems / induction motor assemblies, induction motor control systems, and methods for controlling induction motors, in addition to induction motor controlled compressors in accordance with the teachings of the present invention.

[Description of prior art]
Single phase induction motors are widely used because of their simplicity, robustness and high performance. They apply to general household equipment such as refrigerators, freezers, air conditioners, air conditioning compressors, washing machines, motor pumps, fans and some industrial purposes.

  Known induction motors generally comprise a cage-type rotor and a stator composed of two windings, one winding being a rotating winding and the other being a starting winding. During normal operation of the compressor, AC voltage is supplied to the rotating winding, and the starting winding is temporarily supplied at the start of operation, rotating the magnetic field in the stator gap and accelerating the rotor. , And create the situation needed to get it started.

  Rotating the magnetic field is accomplished by supplying the starter coil with a time lag (preferably close to 90 °) with respect to the current flowing in the main winding. The time delay between the currents flowing in the windings is achieved either by the structural characteristics of the windings or by mounting an external series impedance in series with the starting winding. During the process of starting the engine, the value of the current flowing in the start winding is quite high, requiring the use of switches to cut off the current after the time necessary to promote motor acceleration To do. Once the motor is set to operate, the magnetic field created by the rotating windings interacts with the time induced by the rotor and maintains the rotating magnetic field necessary for the motor to function. .

  Furthermore, with respect to starting this type of motor, a simple voltage application to the stator does not rotate, so means are provided to rotate the motor so that the machine operates.

  A typical example of how to start an induction motor is described in the book of Electric Machines, Ed. McGraw-Hill do Brasil, 1945 by FITZGERALD, A.E., KINGSLEY, C. & KUSUKO, A.

  Due to structural characteristics, induction motors must operate within a limited voltage and frequency range. A supply voltage higher than the specified voltage excites the windings excessively, thereby increasing the magnetic field in the gap and consequently saturating the rotor and stator magnetic fields. As the voltage rises above this point, the current rises very rapidly due to the low reluctance of the magnetic field. On the other hand, a supply voltage much lower than the specified voltage greatly reduces the excitation current of the motor and consequently reduces the torque available on the shaft, in which case the motor can support the normal load applied to that shaft. Eliminates and becomes blocked. A similar situation occurs with frequency changes.

[Disadvantages of the prior art]
As far as the starting form of a single-phase induction motor is concerned, it is feasible to start the motor with today's technology, but such a solution comes from a more complicated configuration. If a capacitor is used in series with the starting winding, good results can be obtained for starting the motor, but the equipment is expensive to make the final solution.

  As far as the voltage level variation problem in limited area networks is concerned, one method used to solve this problem is to employ a large size motor that operates over a wide voltage range. there were. These motors operate below their maximum load, and the motors have traction that can withstand the load even if the supply voltage drops. Also, due to the robustness of the motor, it receives a larger overvoltage without causing overcurrent and overheating problems than a smaller motor. This solves the problem of fluctuations in supply voltage, but requires a large size and weight motor structure, resulting in high cost.

  With respect to the problem of varying frequencies being applied to motors in different regions, the solution is to employ different motors for different frequencies of supply voltage, which makes product and inventory management more complicated, Or it prevents the use of the product in areas with different supply frequencies.

  Another solution that is currently employed is the use of motors with “tap” to select different voltage values in the feed network. This solution solves the problem of voltage fluctuations but requires the adoption of various power switches for switching the taps of multiple voltage motors.

  Another option to solve this problem is the use of a voltage stabilizer associated with the motor. This solution is also less practical and expensive.

[Object of the invention]
An object of the present invention relates to an induction motor control system / induction motor assembly, a system for controlling an induction motor, a method for controlling an induction motor, in addition to a compressor controlled by an induction motor according to the teachings of the present invention. Allows motor operation over a wide range of voltage values.

  It is also an object of the present invention to provide an assembly, system, method and compressor that can modify the applied voltage as a function of the frequency of the feed network.

  Also, according to the teachings of the present invention, one possibility to start a motor that is disconnected or combined with a compressor is foreseen, depending on the use of the starting capacitor.

  Yet another object of the present invention is to prevent overheating of the motor when the network voltage is high to improve its characteristics and expected life.

[Summary of Invention]
In order to solve the problems of the prior art and to achieve the objects of the present invention, the assembly, system, method and compressor of the present invention are single phase induction designed to operate below the normal values of the network. The use of a motor, so that it is always possible to supply power to the motor, and for this purpose the value of the control voltage is lower than the value of the minimum network voltage, ie the value of the network voltage has dropped Be sufficient.

  The size of the motor is determined so that the minimum torque required to start the load is achieved at a voltage lower than the lowest voltage expected in the feed network. This ensures that the torque supplied by the motor is always greater than the minimum required, whatever the voltage conditions supplied by the network.

  To operate the frequency variation in the network, or when the motor is installed at a frequency on the network that is different from the nominal frequency of the motor, to further adjust the motor, the modified nominal voltage of the motor Establishing is anticipated so that the voltage level adjustment necessary to operate the motor at nominal current is used, thereby avoiding problems of low torque, overheating and motor burnout.

The purpose of this invention is, more is achieved assemblies including the induction motor and the induction motor control system, the induction motor has a nominal operating voltage, the control system includes a processing unit, processing units is controlled The control voltage is applied to the induction motor, the network voltage varies from the minimum network voltage, the network voltage has a network frequency, and the induction motor has a nominal operating voltage and a nominal Having an operating frequency, the induction motor has a nominal operating voltage lower than the value of the minimum network voltage, the processing unit measures the network frequency, and there is a difference between the network frequency and the nominal rolling frequency At some point, the processing unit establishes a value for the modified nominal voltage, and the modified nominal voltage is applied to the induction motor. It is, and when the network frequency is equal to the nominal frequency, the processing unit, the value of the control voltage is changed to the level of the nominal voltage.

The object of the present invention is also achieved by means of an induction motor control system,
Comprising a processing unit related to the network voltage,
The processing unit is associated with an induction motor, the induction motor has a nominal operating voltage, the network voltage varies from the minimum network voltage, the induction motor is fed with a control voltage derived from the network voltage, is adjusted by the processing unit, the induction motor has a nominal operating voltage, the value of the minimum network voltage is higher than the value of the nominal operating voltage of the induction motor, processing unit, a function of the variation of the network voltage Adjust the control voltage and apply the network voltage to the induction motor at start-up.

  The object of the invention is further achieved by means of a method for controlling an induction motor, the induction motor having a nominal operating voltage and a nominal operating frequency, the induction motor being fed with a control voltage derived from a change in network voltage, The network voltage has a network frequency, the method comprising: (a) measuring the network voltage, measuring the control voltage, and measuring the network frequency; and (b) measuring the measured network frequency to the nominal operating frequency. And when there is a difference between the network frequency and the nominal operating frequency, establish a modified nominal voltage, and apply a control voltage at the modified nominal voltage to the induction motor; and Adjusting the value of the control voltage to the level of the nominal voltage when the network frequency is equal to the nominal operating frequency.

[Detailed description of drawings]
The invention will be described in more detail in connection with the embodiments shown in the accompanying drawings. As understood from FIG. 1, the electric induction motor 10 is supplied with a control voltage Vc, and the voltage Vc is obtained by adjusting the network voltage Vac. In order to make this adjustment, the central processing unit 8 controls a set of switches 6 and 7, at which time the switches are selectively activated to control the level of the control voltage Vc. The pair of switches 6 and 7 includes a rotation switch 6 electrically connected to the rotation winding of the induction motor 10 and a start switch 7 electrically connected to the start winding of the motor 10.

  In order to monitor the level of the network voltage Vac and the level of the control voltage Vc, first and second voltage measuring devices 4, 11 are seen respectively, both of which are associated with the central processing unit 8. This voltage sensor may be, for example, a resistive divider applied to the analog input of the central processing unit 8.

  Furthermore, a frequency sensor 5 is seen, which is related to the central processing unit 8 and the network voltage Vac. This frequency sensor 5 may be a digital counter of cycles per second caused by the network voltage, an analog that determines the number of cycles that the voltage or any circuit has been carried out on the network voltage within a period of time. It may be a frequency converter.

  In accordance with the teachings of the present invention, system 1 measures the voltage and current applied to motor 10 and adjusts these magnitudes by means of central processing unit 8. In addition to the measurement of the network frequency fac, the control voltage Vc that is actually applied to the motor 10 is measured so that, in accordance with the teachings of the present invention, the network frequency fac is the nominal value of the motor 10 in addition to the form of starting the motor 10. When it is different from the operating frequency fnm, the value of the control Vc can be adjusted.

[Control the level of the control voltage Vc]
As can be seen in FIG. 2, the network voltage Vac varies within a predictable range of the maximum network voltage Vac-max and the minimum network voltage Vac-min. In accordance with the teachings of the present invention, a motor 10 having a nominal operating voltage Vnm lower than the minimum network voltage Vac-min is used in accordance with FIG. The motor 10 should be designed to function at a nominal operating voltage Vmn or an effective voltage value lower than the minimum voltage occurring at the network supply voltage Vac, that is, a voltage below the minimum network voltage Vac-min.

  In this embodiment, the nominal operating voltage Vnm is always kept below the value of the minimum network voltage Vac-min so that it is possible to always supply power to the motor 10 and for this purpose the control voltage Vc Is less than or equal to the minimum network voltage Vac-min, that is, the value of the network voltage Vac can be reduced by adjusting the rotation switch 6. In this control system 1, the motor can be operated in a wide range of the network supply voltage Vac.

[Starting the motor 10]
Advantages obtained from this application of the motor operating in connection with the control system 1 of the present invention, or by means of the control system 1 having an operating voltage Vnm designed to be below the minimum network voltage Vac-min The advantage gained from this application of the controlled motor is that an increase in starting torque can be achieved by applying a voltage higher than the nominal voltage during the starting period, thus requiring the use of a starting capacitor to increase the starting torque. Exists in the fact that there is no sex.

  The advantage is that at the moment of starting the motor 10, for example, the rotation switch 6 and the start switch 7 are commanded so that the control voltage Vc is applied to the motor 10 with the same value of the network voltage Vac. Happens because. A value of the network voltage Vac higher than the value of the nominal operating voltage Vnm ensures a larger current i flowing through the motor 10 and provides the torque necessary to rotate the rotor of the motor 10 without the use of a starting capacitor. . The assembly of the present invention also further prevents the motor 10 from becoming oversized, reducing the metal cost, size and weight in some of these facilities.

In the determined state, as explained above, the network voltage Vac has a very high value and may continue to be applied with the control voltage Vc with the same network voltage Vac. The control voltage Vc applied to the motor 10 may simply be adjusted to a value higher than the nominal operating voltage Vnm of the motor during the motor start-up period. Anyway, medium Hisashisho management unit 8 is always to ensure that impose high control voltage Vc than needed to obtain the nominal torque of the motor 10, that the value of the nominal operating voltage Vnm is designed You should notice.

  Optionally, activation of the motor 10 is for start-up and rotation until the rotor of the motor 10 reaches a nominal rotation speed, or at least has a rotation speed substantially close to the nominal rotation speed. This is done by energizing the windings at the same time, so that a normal function is assured even after a predetermined time has elapsed for motor activation and the activation switch 7 has been turned off.

[Adjustment of the control voltage Vc as a function of the network frequency fac]
In order for the motor 10 to always be in an optimal state, the central processing unit 8 should adjust the control voltage Vc as a function of the change in the network voltage Aac in order to keep the control voltage Vc constant. This is done by measuring the frequency of the network voltage fac by means of the frequency sensor 5, which adjusts the control voltage Vc through the central processing unit 8 to make the motor 10 suitable for normal conditions. To maintain.

  Thus, if there is a frequency change in the network voltage Vac, the control voltage Vc is increased to prevent a decrease or increase in the stator current i of the motor 10 caused by the respective change to the new value of the network frequency fac. Or should be reduced. Current changes caused by variations in the load on the shaft do not affect the output voltage value provided by the controller, and the output voltage value is adjusted only for frequency changes.

  To do this, the assembly of the motor control system 1 / motor 10 should be designed so that the control system 1 is isolated, so that the processing unit 8 can measure the frequency fac of the network, and The measured value can be compared with the value of the motor operating frequency fnm. The latter motor operating frequency fnm is pre-established as a function of the type of motor 10 that is intended to be used. When the processing unit detects a difference between the network frequency fac and the nominal operating frequency fnm, the processing unit 8 should establish a new value for the nominal voltage Vnm (which results in a modified nominal voltage Vnm-a). It is. The value of the changed nominal voltage Vnm-a is proportional to the difference between the network frequency fac and the nominal operating frequency fnm of the motor 10, and the control voltage Vc applied to the motor 10 is changed to the changed nominal voltage Vnm. Has -a.

  With the changed value of the nominal voltage Vnm-a, the system applies a modified control voltage Vc for the new value of the nominal voltage to be applied to the motor 10, and the motor has the nominal voltage Vnm of the motor. Operate at a distinguished voltage level compared to the level. In this way, the current I of the motor 10 is prevented from rising or falling as a function of changes in the network voltage fac.

  In addition to making it possible to achieve appropriate control over the motor 10 in situations where the network frequency fac is not constant, motors designed for a limited network frequency fac can be used in different areas with different network frequencies fac. The problem of use is further prevented.

  The system of the present invention prevents the problem of motor 10 burning or its low torque. This fact can be understood by the following example. If a motor 10 designed to operate at a network frequency fac of 50 Hz is supplied with a network frequency fac of 60 Hz higher than the design, the impedance of the motor will increase and the current i of the motor 10 will decrease, resulting in The torque of the motor decreases. In the opposite situation, a motor 10 designed to operate at a network frequency fac of 60 Hz will be overcurrent i if supplied with a network frequency fac of 50 Hz, and as a result, the motor may overheat and burn out. .

[Control method of motor 10]
In order to control the motor control system 1 of the present invention, the steps of first measuring the network voltage Vac, the control voltage Vc and the network frequency fac are seen.

  The measured value of the network frequency fac should be compared with the nominal operating frequency fac, which is known by the configuration characteristics of the motor 10. If a difference is detected between the measured value of the network frequency fac and the nominal operating frequency fnm, it is concluded that the motor 10 is operating in a non-ideal situation where it is applied to the motor 10. The control voltage Vc to be applied is increased or decreased as described above. This increase or decrease of the control voltage Vc is performed in steps, the processing unit 8 establishes a new value for the control voltage Vc, the modified nominal voltage Vna-a is output, and from this point on. The motor 10 operates under the network frequency fac in this new situation without generating low torque or overheating of the motor.

  When the processing unit 8 concludes that there is no difference between the value of the network frequency fac and the nominal operating frequency fnm, the value of the control voltage Vc is lowered to the level of the nominal voltage Vnm.

  As far as the steps of the method of the invention at the start-up time of the motor 10 are concerned, a control voltage Vc to the motor start-up winding, which is equal to the network voltage Vac, is applied, and such applied voltage causes the motor to reach the nominal rotational speed. It must be maintained for a start-up time that is substantially close and sufficient for normal rotation.

  As described above, in the determined situation, the network voltage Vac has a value that is too high for the application of the control voltage Vc at the same level of the network voltage Vac, so during the start-up the motor 10 The control voltage Vc applied to is simply adjusted to a value higher than the nominal operating voltage Vnm.

  Furthermore, according to the teachings of the present invention, the compressor driven by the motor 10 should be provided with the control system 1 described above. The compressor may then be employed in connection with the control system 1 or separately from the control system.

  While preferred embodiments have been described, it is to be understood that the scope of the invention includes other possible variations, is limited only by the content of the appended claims, and includes equivalents thereof.

Block diagram of the system of the present invention Time chart showing network voltage function

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control system 4 Voltage measuring device 5 Frequency sensor 6 Switch for rotation 7 Switch for starting 8 Central processing unit 10 Electric induction motor 11 Voltage measuring device

Claims (15)

An induction motor (10) Control system (1) is an assembly comprising a single-phase induction motor having a nominal operating voltage (Vnm) (10),
Wherein the control system (1) comprises a processing unit (8),
Before Kisho management unit (8), the level of the network voltage (Vac), to adjust the level of the control voltage (Vc),
The control voltage (Vc) is applied to the induction motor (10),
The network voltage (Vac) varies from the minimum network voltage (Vac-min),
The network voltage (Vac) has a network frequency (fac), and the induction motor (10) is designed for a nominal operating voltage (Vnm) and a nominal operating frequency (fnm);
The induction motor (10) has a nominal operating voltage (Vnm) lower than the minimum network voltage (Vac-min), the processing unit (8) measures the network frequency (fac), and the network frequency (fac) When there is a difference between the operating frequency (fnm), the processing unit (8) establishes the value of the modified nominal voltage (Vnm-a), which is the modified nominal voltage (Vnm-a) Applied to the induction motor (10), and
An assembly wherein the assembly is characterized such that when the network frequency (fac) is equal to the nominal operating frequency (fnm), the processing unit changes the value of the control voltage (Vc) to the level of the nominal voltage (Vnm).   The modified nominal voltage (Vnm-a) value is modified as a function of the network frequency, and the modification includes the network frequency (fac) value and the nominal operating frequency (fnm) of the induction motor (10). The assembly of claim 1, which is proportional to the difference between the two.   The processing unit (8) reduces the value of the network voltage (Vac) to the value of the control voltage (Vc), the value of the control voltage (Vc) being lower than the value of the minimum network voltage (Vac-min). The assembly according to 1 or 2. The processing unit (8) comprises first and second voltage measuring devices (4, 14),
The first voltage measuring device (4) measures the network voltage (Vac) and the second voltage measuring device (11) measures the control voltage (Vc). Assembly. Control system (1) comprises a set of switches controlled by a processing unit (8) (6, 7), the set of switches (6, 7),
A rotation switch (6) electrically interconnected to the rotation winding of the induction motor (10), and an activation switch (7) electrically interconnected to the activation winding of the induction motor (10). And
Starting winding, when the induction motor (10) is activated, is selectively activated by treatment unit (8),
Processing unit (8) The assembly of claim 4 wherein applying the network voltage (Vac) and starting winding and a rotating winding. Processing unit (8) when a preset time for starting the motor is completed, the assembly of claim 5, wherein issuing a command to turn off the switch (7) Starting the winding of the induction motor (10) . A control system of an induction motor (10) (1), comprising a processing unit related to the network voltage (Vac) (8) As a processing unit (8) is associated with the induction motor (10),
The induction motor (10) has a nominal operating voltage (Vn), the network voltage (Vac) varies from the minimum network voltage (Vac-min),
Induction motor (10), the network voltage (Vac) from the obtained control voltage (Vc) is supplied, the control voltage (Vc) is adjusted by the processing unit (8),
The induction motor (10) has a nominal operating voltage (Vnm)
The minimum network voltage (Vacmin) value is higher than the nominal operating voltage (Vnm) value of the induction motor (10),
Processing unit (8) as a function of the variation of the network voltage (Vac), by adjusting the control voltage (Vc), and, at startup, to apply to the induction network voltage (Vac) Motor (10) A system that is characterized by the system. First and second voltage measuring devices (4, 11);
A frequency sensor (5) for measuring the network frequency (fac) of the network voltage (Vac),
The induction motor (10) has a nominal operating voltage (Vnm) lower than the value of the minimum network voltage (Vac-min),
The processing unit (8) measures the network frequency (fac)
When there is a difference between the network frequency (fac) and the nominal operating frequency (fnm), the processing unit (8) establishes a value for the modified nominal voltage (Vnm-a) and the modified nominal voltage. The value of (Vnm-a) is modified as a function of the nominal frequency, and the modification is proportional to the difference between the network frequency (fac) and the nominal operating frequency (fnm) of the induction motor (10), and the change The nominal voltage (Vnm-a) applied is applied to the induction motor (10),
The system according to claim 7, wherein when the network frequency (fac) is equal to the network frequency (fac), the processing unit changes the value of the control voltage (Vc) to the level of the nominal voltage (Vnm). A starting switch (7) electrically connectable to the starting winding of the induction motor (10);
The start winding is activated by the start switch (7) by the processing unit (8) when the induction motor (10) starts.
9. The system according to claim 8, wherein the processing unit (8) applies a network voltage (Vac) to the starting winding.   The processing unit (8) applies a network voltage (Vac) for start-up time, the start-up time corresponding to a time sufficient for the induction motor (10) to be substantially at nominal rotational speed. 10. The system according to 9. A method for controlling an induction motor (10), the induction motor (10) has a nominal operating voltage (Vnm) and a nominal frequency (fnm), and the induction motor (10) regulates a network voltage (Vac). And the network voltage (Vac) has the network frequency (fac).
A step that measure the network voltage (Vac), the control voltage (Vc) and the network frequency (fac),
Comparing the measured network frequency (fac) value to the nominal operating frequency (fnm);
When there is a difference between the network frequency (fac) and the nominal operating frequency (fnm), the value of the modified nominal voltage (Vnm-a) is established and controlled with the modified nominal voltage (Vnm-a) Applying a voltage (Vc) to the induction motor (10);
Adjusting the control voltage (Vc) to the level of the nominal voltage (Vnm) when the network frequency (fac) is equal to the nominal operating frequency (fnm).   12. Method according to claim 11, comprising the step of applying a control voltage (Vc) equal to the network voltage (Vac) to the starting and rotating windings of the induction motor (10) prior to starting the motor (10). .     12. A method according to claim 11, comprising the step of applying a control voltage (Vc) lower than the network voltage (Vac) to the starting and rotating windings of the induction motor (10) prior to starting the motor (10). .   The application of the network voltage (Vac) to the starting winding of the induction motor (10) is maintained with respect to the starting time, which is sufficient for the induction motor to be substantially at nominal rotational speed. The method according to claim 12 or 13, corresponding to:   Compressor driven by an induction motor (10) comprising a control system (1) according to any one of claims 7 to 10.

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