• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    An induction motor of the squirrel-cage type is driven from a polyphase power line through the intermediary of two cascaded thyristor arrays converting the line current into an adjustable rectified current and reconverting the latter into a stator current of variable frequency. The magnitude of the rectified current is varied via the first thyristor array, under the control of a tachometric signal from a speed sensor coupled with the rotor of the machine, to maintain the rotor speed at a selected level within a predetermined dynamic range in which the stator current varies approximately in proportion to the slip frequency under changing load. The slip frequency is adjusted by the second thyristor array under the control of an arithmetic unit which receives the tachometric signal along with a voltage feedback from the stator input and which maintains the stator voltage substantially proportional to rotor speed in order to stabilize the excitation current of the motor. The maximum value of the tachometric signal fed to the arithmetic unit is limited by a clamping circuit to allow the selection of rotor speeds above the dynamic range without further increases in power.
    公开号:SU871746A3
    申请号:SU772533350
    申请日:1977-10-04
    公开日:1981-10-07
    发明作者:Вольф Хорст
    申请人:Цинзер Текстильмашинен Гмбх (Фирма)；
    IPC主号:
    专利说明:

    (54) DEVICE FOR REGULATING THE NUMBER OF TURNOVERS OF AN ASYNCHRONOUS MOTOR The invention relates to electrical engineering and can be used in frequency-controlled electric drives based on an induction motor. A device for controlling the speed of an asynchronous motor is known, comprising a current measuring unit, the output of which is connected to a slip frequency setting unit through a comparison unit. The output of the latter through the frequency adder, where the output of the tachogenerator is connected, is connected to the frequency control unit of the converter to which the induction motor is connected. A disadvantage of the known devices is that as a result of a rapid change in load, the frequency of the converter changes almost without lining, and the current no, which can lead to a decrease in the overload capacity of the engine and its overturning in a transient mode. It is also known a device for controlling the speed of an asynchronous motor with a squirrel cage and a tachogenerator on a shaft containing a current inverter, the output of which is connected to an asynchronous motor, and the input through the inductor is connected to an adjustable rectifier, the control circuit of which is connected to the regulating current asynchronous motor, voltage measuring unit at the terminals of the induction motor, frequency adder, to one input of which the output of the tachogenerator is connected, to another task unit slip and the output of the frequency adder is connected to the control input of the current inverter, and the output of tachogenerator 2 is connected to the first input of the slip frequency setting unit. The disadvantage of the known device is that as a result of a sudden change in load torque, the current quickly changes, and are the surge overvoltages on the inverter, which reduces its reliability. The purpose of the invention is to increase the reliability of the device. This goal is achieved by the fact that, in this device, the output of the voltage measuring unit at the terminals of the induction motor is connected to the second input of the slip frequency setting unit. In addition, the slip frequency setting unit is designed as a proportional controller. At the bottom of the diagram presented the device. The device comprises an asynchronous motor 1. In this preferred embodiment, a three-phase motor is meant that operates in both engine mode and generator mode. It may have a predominantly short-circuited rotor. Its rotor shaft 2 is associated with load 3 and tachogenerator 4. Tachogenerator 4 generates either a constant voltage, proportional to the rotation speed poTop i of the motor, or produces a three-phase current, which is then rectified. The three-phase current network 5 is via a two-way switch b under the key. To an adjustable rectifier 7, the control inputs of which are connected to the current control unit 8. The output of the tachogenerator 4 is connected via a power supply 9 to an adder 10 and a frequency-frequency unit 11, the output of which is connected to the control input of the field current regulator 12. A block 13 is connected to a block 13 for measuring voltage at the terminals of an induction motor. The current leads 14, 15, 16 to the controller 12 and the adder 10 can be intermittently included not shown adjustable resistance to establish the desired constants C, C 2, C so that the signal C. U is applied to the point of the block 11 through the current lead 14 (Ug is the voltage at the stator terminals and through the current supply 16 signal, and the adder 10 is applied through the current supply 15 signal CjU (U the output voltage of the tachogenerator proportional to the speed of rotation of the rotor.) C 2 and Cj can be known under the conditions equal to the value. torus 12 may have an operational boost 17 with a non-characteristic, formed by a resistor 18, which connects the input and output of the amplifier with the help of wire 19. The output of controller 12 is connected to the input 20 of adder 10, the output of which through a voltage-frequency converter 21 and a distributor 22 pulses are connected to an inverter 23. The device contains a block 24 SSC and amp; no slip frequency and an inverter power supply circuit dross 25. The device operates as follows. Amplifier 17 Generates a constant voltage signal at the output, proportional to the deviation, adjusts the magnitude, i.e. difference with. . It determines the slip frequency of the rotor, which is supplied to the second input of the adder 10 to add to the DC voltage passed through the current lead 15. The regulator 12 is designed in such a way that the slip frequency of the rotor is constantly less than the frequency difference between the critical and synchronizing points of the torque characteristic — the stator frequency of the engine 1, so that the engine 1 does not exceed the limit slip under permissible loads. The excitation current, regulated by means of the regulator 12, at a constant rotor speed, i.e. with U const, it is set to a constant value. In a very wide range of rotational speeds, the excitation current remains unchanged regardless of the load. The localization at the terminals of the engine 1 is formed in accordance with the stator current and the slip frequency of the rotor. By adjusting the regulator 12 by acting on the slip frequency of the rotor at a given rotational speed, it is kept approximately constant. Regulation occurs in such a way that at each rotational speed set by a given value, at nominal torque, there is approximately the optimum slip frequency of the rotor for optimal use of engine 1. The difference is applied to block 11, while ensuring that the voltage at the engine terminals 1 is proportional to the speed of rotation of the rotor. The output of the adder 10 is connected to a converter 21, the output of which sends DC amplitude control pulses whose frequency is proportional to the input voltage of the converter 21. These control pulses through the distributor 22 are applied to the keys of a static inverter 23 forming a shedtimpulse, fully controlled three-phase current bridge, for obtaining a three-phase current of the stator of the asynchronous motor 1. To start the engine 1, it is necessary that the controller 12 sets the rotor sliding to the start of the start, which is achieved with by turning on the unit 24 for only a short time to start. By taking a closer look at the regulation of the excitation current, which is understood to be the net reactive current of the engine. .,.,. The vector lg (g 1ok stator, is the rotor current, 1 is the excitation current). For an asynchronous motor to work flawlessly, it is necessary in the same way as with a shunt machine of direct current. - so that there is always enough excitation energy. But in a DC shunt machine, it is relatively simple, since separate terminals of the core and the excitation circuit do not need to be achieved, to achieve constant excitation regardless of the load. An asynchronous motor, on the contrary, has common terminals for a current of all currents. and for rotor currents (the rotor current is proportional to the moment of rotation of the load current), and for the excitation current, so that the excitation current of the induction motor at a constant rotor speed cannot perceive the action or maintain a constant value regardless of the rotor current. However, this is achieved with the aid of the regulator 12. A prerequisite for this is that with each load change over a short time, for example from 0.1 to 0.2 s, an approximately constant stator current is maintained due to smoothing current by the coil inductance of drossel 25, the separation of the stator current into the excitation current and the rotor current (as load current / is carried out with the help of the regulator 12 by changing the slip frequency of the rotor. The constant excitation current and thus the DE (Vector electromotive force) is achieved by changing the rotor current. The rotor current from its side through the resistance R, (the rotor and the caNWM through the slip frequency uf of the rotor is impacted in such a way that the excitation current always and regardless of the load retains its optimal value ( R is the total equivalent active resistance of the rotor; fg is the frequency of the stator current, uf is the hourR is the self-slip of the rotor, the rotor resistance).
    Regulation of the excitation current is, firstly, the goal, to create a favorable dynamic mode of the asynchronous motor, approximately corresponding to the mode of the DC shunt machine, secondly, this regulation of the excitation current is aimed at maintaining a constant voltage at a given speed of rotation. clamps and with a sudden load change. The voltage at the terminals varies according to the set rotational speed of the rotor, namely, approximately proportional to the rotational speed of the rotor. Due to the controller 12, it is possible to maintain the excitation current approximately constant regardless of the rotor current, at a constant speed. This is explained as follows. It is assumed that an asynchronous motor 1 with a constant rotational speed drives a constant load. If then a sudden decrease occurs.
    load, for example, the load drops, then, due to the inductance (drossel 25), the stator current remains for a short time even, for example, from 0.05 to 0.2 s, approximately constant. The rotational speed of the rotor in this short time can also increase only relatively slightly. In this case, the regulator 12 operates inertia-free in such a way that the voltage on the terminals, despite the shedding of the load and a slight increase in the speed of rotation, always remains proportional to the speed of rotation. This he achieves thanks to the fact that
    5, the output voltage of the tachogenerator 4 varies in proportion to a slight increase in the velocity of injection and, accordingly, the internal resistance increases without inertia.
    0 engine 1. An increase in internal resistance is achieved by reducing the slip frequency of the rotor. At the same time, however, with a certain delay, the stator current decreases through the current regulator and the moment
    5, the rotation of the engine 1 is such that the established rotational speed is again reached. Without controller 12 due to a change in the load voltage on the stator
    0 would immediately increase greatly, which, for example, could easily lead to the destruction of the keys of the inverter 23. However, the controller 12 maintains the voltage on the stator, despite the sudden
    5 change of load is approximately constant. As the load decreases, the rotor immediately starts to increase its rotational speed with a subsequent decrease in the rotor speed,
    0 then, due to this, the internal resistance of the motor 1 is greatly increased and, accordingly, the voltage on the stator rises sharply. This increase in voltage across the stator is much faster than
    5 an increase in the rotational speed of the rotor, so that at the input of the regulator 12 there also appears a deviation of the regulated value, which by means of the regulator 12, the adder 10, the converter 21,
    0 of the distributor 22, the control frequency of the inverter 23 is almost inertia-freely increased so that the slip frequency of the rotor due to an increase in the stator frequency becomes
    5 somewhat more. But as the slip frequency increases, the internal resistance of the motor decreases, as a result of which the voltage across the stator decreases again. Because of this again
    0, the deviation of the controlled variable is reduced, so that the slip frequency becomes less, the voltage across the stator then increases again. These processes occur so quickly that
    5, the voltage across the stator, even with a sudden extreme change of load, is continuously and without occurrence of voltage peaks regulated by an approximately constant value, thus the excitation current is also regulated by Ma an approximately constant value regardless of the load; so it is also possible to talk about the regulation of the excitation current, although the excitation current itself is not measured, the internal resistance of the motor 1 varies in the average time value in accordance with the change in the stator current due to the load change. Thus, despite the sudden drop in load, the nominal voltage loss on the stator of the motor 1 decreases, and at the same time, the excitation current, regardless of the load, is kept close to constant. As a result, the effect is achieved that with any load changes, even at the fastest, the voltage across the stator and the excitation current at this rotational speed remain approximately constant and dangerous dangerous overvoltages cannot occur. Adjusting the rotational speed is much more inertial than regulating the excitation current, and according to the described initial process, until the stator current decreases, until the stator current again corresponds to the reduced or lacking load of the asynchronous motor. On the other hand, if a sudden increase in load occurs, for example, a sudden start of load, then the frequency of the slide of the rotor immediately increases, which greatly reduces the internal resistance of the motor and decreases the voltage on the stator, etc., so that the regulator 12 is practically Inertia-free also regulates an approximately constant voltage across the stator and, thus, an approximately constant excitation current. The unit raises the current 8 of the stator to those things until it reaches the magnitude required for a higher torque. The advantage of controlling the excitation current of the engine 1 is also that the slip frequency of the rotor With a constant torque of the drive 1, regardless of the speed of rotation of the rotor, is approximately constant and changes, therefore, as little as possible depending on the moment of rotation. This provides significant advantages also for starting and stabilizing regulation in dynamic processes. Thus, the effect is achieved that at a given rated current and accordingly at a given rated load, the slip frequency of the rotor takes place, the most favorable for the operation of an induction motor. This is easily achieved by properly matching the constants C, C, and Cd, with C, 2, and Cd being equal in magnitude. The controller 12 in this embodiment is a multi-amplifier P controller, with only a very small proportionality of this controller, so that in stationary operating modes the deviation of the controlled variable is almost zero and the ca # tM is practically. Of course, it is advisable to adjust the magnitude of the controlled excitation current to the nominal excitation given by the manufacture of the asynchronous motor. Instead of P-regulators, other suitable regulators, preferably PI-regulators, should also be provided. Although the rotational speed of the engine 1 can preferably be adjusted, the proposed device also has the advantage if the setpoint of rotational speed does not change and the stator frequency deviates from the line frequency. As long as, due to the rectifier 7, the voltage of the tachogenerator 4 increases in proportion to the speed of rotation of the rotor and the voltage on the stator increases in proportion to the speed of rotation of the rotor, the maximum output power of the induction motor 1 increases in proportion to the speed of rotation of the rotor and decreases again with decreasing speed the rotor is proportional to it. In addition, the device allows, in addition to this speed control range, to provide another, higher speed control range for the induction motor, in which the maximum power output of the machine remains constant. This is due to the fact that a voltage limiter, not shown in the drawing, is intermediately connected in the conductor 16, which, starting from a predetermined rotor speed, prevents the voltage in the conductor 16 from rising, if the rotor speed increases and further, t . in this upper range of rotational speed, the voltage in the conductor 16 is supported. lives permanently. Due to such a current limiter in the conductor 16 in this upper rotational speed range, the induction motor maintains a mode approximately corresponding to the DC shunt machine in the rotational speed control range, which characterizes the so-called field weakening range, therefore, in another rotational speed control range to which the voltage in the current collector 16 varies in proportion to the output voltage of the tachogenerator 4, the motor maintains a mode approximately corresponding to the mode of a shunt machine of direct current, in the so-called control range.
    The adder 10 summarizes the signals supplied to it. If the signal supplied to it from controller 12 is negative, which takes place in the generator mode due to a change in voltage at the terminals of the engine 1, then this corresponds to the summation of the negative signal with the received positive signal supplied to the adder 10 from the tachogenerator 4 through the conductor 15. Negative addition can also be denoted as subtraction, so by summation in this case it should also be understood as the principle of subtraction. Thus, instead of producing negative addition, it is also possible to provide that the output of the regulator 12, when switching from the engine mode to the generator mode, does not change its polarity, in which case the adder 10 should be switched from summation to subtraction, or in this case this, in the conductor passing from the regulator 12 to the adder 10, when the generator is in mode, it is possible to additionally turn on the inverter, only in generator mode the inverting output signal of the regulator 10.
    Thus, by adjusting the slip when the voltage at the terminals of the motor is changed, an overvoltage on the inverter arms is eliminated and its reliability is increased.
    权利要求:
    Claims (2)
    [1]
    1. A device for controlling the speed of an asynchronous motor with a squirrel cage and a tachogenerator on a shaft containing a current inverter, to the output of which
    0 an asynchronous motor is connected, and the input through the inductor is connected to an adjustable rectifier, the control circuit of which is connected
    with an asynchronous motor current control unit, a voltage measuring unit at the terminals of an induction motor, a frequency adder, to one input of which an output is connected. A tachogenerator, to the other a task unit
    0 is the slip frequency, and the output of the frequency adder is connected to the control input of the current inverter, with a tachogenerator output different to the first input of the slip frequency setting block
    5 by the fact that, in order to increase the reliability of the device, the output of the voltage measuring unit on the asynchronous clamping terminal is connected to the second input of the set slip frequency unit.
    0 engine
    [2]
    2. The device according to claim 1, characterized in that the block for setting the slip frequency is made in the form of a proportional controller.
    five
    Sources of information taken into account in the examination
    1. The patent of Germany No. 1463344, cl. 21 C 59/10, 1912.
    2. The patent of the Federal Republic of Germany 2234681, cl, H 02 R 5/36, 1972.
    0
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