RU2076450C1 - Method for regulation of rotation frequency of double-supply electric motor and device which implements said method - Google Patents

Abstract

FIELD: double-supply electric motors. SUBSTANCE: method involves supply of stator windings of electric motor from three-phase line and supply of rotor windings from frequency converter. When electric motor reaches rotation frequency which is greater than stator field rotation, alternation of stator windings is changed, voltage which supplies rotor windings is altered simultaneously. Angle for conducting thyristors of inverter of frequency converter is kept constant, it is equal to 150 degrees during regulation of rotation frequency. Corresponding device has phase switching unit, which matches phase alternation in power circuit and in inverter control circuit. EFFECT: increased range of rotation frequency regulation. 2 cl, 3 dwg

Description

 The invention relates to electrical engineering, in particular to the field of adjustable asynchronous electric drive based on a dual-power motor.

A known method of controlling a dual-power machine, according to which the stator winding is connected to the network, and the rotor winding to an adjustable frequency converter, measure the instantaneous currents in the phases of the rotor, amplify these signals and apply to the control electrodes of the frequency converter, and the gain is chosen so as to provide critical slip of the engine, engine speed is controlled by changing the frequency of the setpoint [1]
The disadvantage of this method is the complexity and low reliability of the regulatory process, because To control the frequency, it is necessary to perform forced switching of the thyristors of the inverter supplying the rotor winding, and for stable operation of the motor in a wide speed range, the control signal must be changed as a function of the rotor current of the motor.

Closest to the claimed one is a known method of controlling the rotational speed of a dual-supply motor, in which the stator winding is supplied with a constant amplitude voltage, and the rotor winding is controlled by a voltage from a frequency converter, instantaneous values of linear voltages between the phases of the rotor windings are measured, the switching moments of the inverter keys of the frequency converter By switching the keys of the inverter, the set motor speed is set, and the speed is controlled by by varying the value of the voltage supplied to the winding of the rotor [2]
However, the known method of controlling the engine speed has the following disadvantages. Only one-zone speed control is carried out when the direction of rotation of the rotor of the induction motor is opposite to the direction of rotation of the stator field. As a result, the range of regulation of the engine speed is limited by the maximum permissible value of the EMF in the rotor winding, since the higher the rotor speed, the greater its EMF, and if the maximum permissible voltage value in the rotor windings is exceeded, a breakdown of the rotor insulation is possible. When controlling speed and in steady state, the engine operates in the anti-inclusion mode. Therefore, the maximum rotor speed is two to three times higher than the frequency of rotation of the stator field. In addition, the opening angle of the inverter keys changes in the process of controlling the rotation frequency, which leads to nonlinearity of the mechanical characteristics of the electric drive and impairs the operation of the inverter of the frequency converter.

In the proposed method, controlling the rotational speed of the dual-power motor, a constant amplitude voltage is supplied to the stator winding, and a constant amplitude voltage is supplied to the stator winding, and an adjustable three-phase voltage directed opposite to the rotor winding EMF and exceeding it is supplied to the rotor winding through a frequency converter with a DC link in size. The instantaneous values of the three-phase voltage at the terminals of the rotor windings are measured, the phase of the measured three-phase voltage is shifted by a constant angle of delay. The moments of switching the keys of the inverter of the frequency converter are determined by shifting the moment of applying the control signals to the keys of the inverter by the maximum permissible delay angle of 150 ^o relative to the points of natural switching of the keys of the inverter.

 Turn on the inverter keys with a constant angle of delay relative to the points of natural switching of the inverter keys. By changing the value of the voltage supplied to the rotor winding, by changing the reference signal at the input of the frequency converter, the engine speed is adjusted until it becomes larger than the speed of the stator field. After the engine accelerates to a rotation speed exceeding the rotational speed of the stator field, the alternation of the phases of the voltage in the stator winding of the motor is changed, while the voltage of the reference at the input of the frequency converter is reduced. By changing the magnitude of the voltage supplied to the rotor winding by changing the reference signal at the input of the frequency converter, the engine speed is controlled at values exceeding the rotational speed of the stator field of the motor.

 In this method, dual-zone speed control of the dual power motor is performed. In the first zone, at low speeds, the dual-power motor develops a motor moment, although the direction of rotation of the rotor is opposite to the direction of rotation of the stator field. This is achieved due to the fact that the voltage at the output of the frequency converter is greater than the rotor EMF, and the current in the rotor windings is directed counter-EMF. With an increase in the rotor speed, which rotates against the direction of rotation of the stator field, the rotor EMF increases, and when the rotor speed exceeds the rotational speed of the stator field, the rotor EMF exceeds the starting value by more than two times. Therefore, after the engine accelerates to a rotation speed exceeding the stator field rotation frequency in magnitude, the dual-supply motor is transferred to the second zone of operation at high rotation speeds.

 To do this, change the phase rotation of the voltage in the stator winding, thereby changing the direction of rotation of the stator field. Now the stator field rotates in the same direction as the previously rotated engine rotor, and the rotor speed exceeds the rotational speed of the stator field. In this case, the magnitude of the EMF of the rotor winding decreases after changing the phase rotation of the voltage in the stator, therefore, to reduce the motor current simultaneously with the phase rotation of the stator, the reference voltage at the input of the frequency converter is reduced to such a value that the voltage at the output of the frequency converter exceeds the EMF of the motor rotor. The voltage at the output of the frequency converter exceeds the rotor EMF and is directed in the opposite direction; therefore, the rotor current of the motor rotating in the same direction as the motor stator field is directed counter to the rotor EMF. The dual-power engine develops a motor torque at a rotor speed of the motor exceeding the rotational speed of the stator field, and the rotor and stator field rotate in the same direction.

 In the second control zone at high speeds, as well as in the first control zone at low speeds, to increase the engine speed, the reference voltage at the input of the frequency converter is increased, to reduce the engine speed, the reference voltage at the input of the frequency converter is reduced.

 In this method of controlling the rotational speed of a dual-power motor, the inverter of the frequency converter operates in the current inverter mode, driven by the voltage taken from the terminals of the rotor windings, with a constant angle of the opening delay of the inverter keys. This increases the reliability of the inverter, eliminates the possibility of overturning. The inverter operates in a current inverter mode, driven by the voltage at the outputs of the rotor winding.

 The transfer of the dual-supply motor to the second regulation zone by changing the phase sequence of the stator winding voltage while decreasing the reference voltage at the input of the frequency converter after exceeding the rotor speed of the level equal to the stator field rotation frequency allows expanding the range of regulation of the engine speed by more than 2 times, because After changing the phase rotation, the slip of the EMF of the rotor winding decreases.

 Figure 1 presents a functional diagram of a device in which a method for controlling the rotational speed of a dual power engine is implemented; figure 2 is a schematic diagram of a device that implements the method; figure 3 is a vector diagram explaining the operation of the phase-shifting device.

 A device for controlling the rotational speed of a dual-power motor contains a frequency converter, the inverter of which is made according to a three-phase bridge circuit with keys (thyristors) 1-6, the DC terminals of which are connected to the output of a three-phase controlled bridge rectifier 7, the power input of which is connected to the transformer 8 network, and the control input to the voltage regulator 9. The inverter AC terminals are connected to the phase terminals of the rotor winding 10 of the dual power motor 11.

The inverter control unit contains a phase switching device 12 having a reversing contact 13, the coil of which is connected to the mains through the make contact 14 of a centrifugal relay mounted on the same shaft as the motor 11, and the main switching contacts 16 of the reversing contactor are included in two phases of the stator winding 17 of the motor 11 , the first auxiliary switching contacts 18 of the contactor 13 are connected in a circuit between two phases of the motor rotor winding and two primary windings of a phase-shifting transformer at an angle of 150 ^o Mator 19, assembled in a zigzag star pattern. The second auxiliary switching contacts 20 of the contactor 13 are connected between the two secondary windings of the transformer 19 and the two inputs of the timing device 21. The third primary winding of the transformer 19 is connected directly to the third winding of the motor rotor, and the third secondary winding of the transformer 19 is connected directly to the third input of the timing device 21 the output of which is connected to the input of the pulse shaper 22, the output of which is connected to the control input of the inverter. Phase shifting device with a phase angle of 150 ^{o is} made in the form of a three-phase transformer connected according to the "zigzag star" circuit, having conclusions 24-26 for connecting the primary winding, and conclusions 27-29 for connecting the secondary winding.

 The timing device 21 is made in the form of a three-phase bridge 30 assembled from LEDs of dinistor optocouplers 31-36, a resistor 37 is connected to the output of the bridge 30. The pulse shaper 22 is composed of optocoupler dinistors 31-36 connected to the control electrodes of the thyristors, respectively 1-6, and the anode of each of the optocoupler dinistors is connected to the anode of its thyristor, and the cathode of the dinistor to the control electrode of this thyristor.

The method of controlling the speed in the device is as follows. A voltage of constant amplitude and frequency is supplied to the stator winding of the motor 11 through switching contacts 16, and an adjustable three-phase voltage is supplied to the winding of the rotor 10 through a frequency converter. The voltage at the output of the rectifier 7 is set by the setter 9. When current flows through the stator windings of the motor 11, an EMF is induced in the rotor windings. The three-phase voltage from the terminals of the rotor winding 10 is fed through the switching contacts 18 to the three-phase phase-shifting device 19, which moves the phase by an angle of α 150 ^o .

A two-position phase switching device 12 connects the corresponding phases of the inverter control unit to the corresponding phases of the motor rotor winding. For any of the two positions of the reversing contactor 13 at the primary winding of the transformer 23, input 24 is connected to phase A of the rotor winding, voltage U _{A is} connected to this transformer winding, input 25 is connected to phase B of the rotor winding, voltage U _{B is} connected to this transformer winding, input 26 is connected to phase 6 of the rotor winding, voltage U _{C is} connected to this transformer winding. The secondary windings of the transformer 23 are connected by a zigzag, so that at the output 27 the voltage U ₁ U _B U _A , shifted by an angle of a 150 ^o el. in relation to the voltage U _A , the output 28 voltage U ₂ U _C U _B , the output 29 voltage U ₃ U _A - U _C. The transformer 23 is a phase-shifting device with a phase shift a 150 ^o el. For any of the two positions of the reversing contactor 13, at the secondary side of the transformer, terminal 27 is connected to the shoulder of the LED bridge of the timing device 21 controlling the inverter phase A thyristors, terminal 28 is connected to the shoulder of the LED bridge controlling the inverter phase B thyristors, terminal 29 is connected to the shoulder LED bridge controlling the thyristors of phase C of the inverter.

The vector diagram (figure 3) of the voltage on the secondary windings of the transformer 23 explains the operation of the phase-shifting device with a phase shift of a 150 ^o . Thus, a shift of 150 ^o el. points of natural switching LEDs of optocouplers connected by a three-phase bridge circuit, relative to the points of natural switching of the inverter keys, which are controlled by these LEDs.

ω_o частота вращения поля статора;
ω частота вращения ротора.Using the control unit according to the indicated principle, thyristors 1-6 of the inverter are alternately switched in such a way as to ensure that the current flows through the phases of the rotor winding 10 towards the rotor EMF. The inverter operates in current inverter mode. The motor will rotate in the opposite direction to the rotation of the electromagnetic field generated by the stator winding. The rotor will have a slip:

ω _{o the} frequency of rotation of the stator field;
ω rotor speed.

EMF of the rotor winding will be:
E _p E _pn • S
where E _ph emf of the stationary rotor.

As the rotor accelerates, the slip S increases, the EMF in its winding E _p increases, the current decreases, and the motor torque decreases. In the steady state, the rotor rotates with a frequency at which equality is observed:
U _α = E _and + I • R _e + 2ΔU _t (1)
where U _{α the} voltage at the output of the rectifier 7;
E _and against inverter EMF;
I input current of the inverter;
R _{e is the} equivalent motor resistance reduced to the inverter output.

DU _t direct voltage drop on the open inverter thyristor.

To regulate the rotation frequency ω of the engine 10 in the first zone having a rotation frequency w ₁ , with the help of the adjuster 9, the voltage U _α at the output of the rectifier is changed. As a result, the fulfillment of condition (1) is violated, the rotor current changes, the rotational speed, the EMF of the motor rotor changes until the EMF reaches a new value at which relation (1) is satisfied. The engine will be in steady state with a new speed value w ₂ .

а ЭДС ротора
E_p E_рн • S 2Е_рн
если

E_p E_рн • S 3E_рн
и т.д.The speed control in the first zone is carried out until the speed reaches a value at which the rotor EMF will have a maximum permissible value, which is determined by the properties of the rotor insulation. If the rotor speed is equal to the frequency of rotation of the stator field, then the slip:

and the rotor EMF
E _p E _ph • S 2E _ph
if a

E _p E _ph • S 3E _ph
etc.

Therefore, when the motor speed ω is exceeded, the field rotation speed w _{o is} changed, the phase rotation of the voltage supplied to the stator winding is changed and the motor is transferred to the second speed control zone.

The frequency of rotation at which the phase rotation of the voltage in the stator winding is changed can be selected in the range;
1,1ω _o <ω <2ω _o
When the specified speed is reached, the centrifugal relay 15 is activated, closes its contact 14, the coil 13 of the reversing contactor receives power and its contacts 16, 18 and 20 are switched to the second position.

The phase rotation of the voltage supplied to the stator winding changes, the direction of rotation of the stator field of the motor changes, the phase rotation of the EMF of the rotor winding changes, however, the phase-switching device 12 ensures the normal operation of the inverter, also changing the phase rotation in the inverter control unit. After reversing the voltage in the stator winding, the stator field rotates in the same direction as the rotor, however, the rotor rotational speed is greater than the field rotation speed; therefore, the EMF is lower in the rotor than the EMF before changing the phase rotation. To limit the current in the rotor winding by the master 9, the voltage U _α at the output of the rectifier is reduced. Current along the phases of the rotor winding still flows towards the rotor EMF, however, the motor rotates in the direction of rotation of the field at a speed higher than the speed of rotation of the field, that is, it works in the second zone of "high" speeds. As the rotor accelerates, the EMF in its winding increases, the current decreases and the motor torque decreases. In the steady state, the rotor rotates with a frequency at which equality (1) is observed.

To regulate in the second zone of the rotational speed w of the motor 11, which had in steady state the value of the rotational speed w ₃ , with the help of the adjuster 9, the voltage at the output of the rectifier is changed. As a result, the fulfillment of condition (1) is violated, the current of the motor rotor changes, the frequency of rotation and the EMF of the motor rotor change until the EMF reaches a new value at which relation (1) is satisfied. The engine will operate in steady state with a new speed value.

 As a result of work in the second zone of regulation of the engine speed, when the rotor rotates in the direction of rotation of the field with a speed higher than the field rotation speed, and the current in the rotor winding flows towards the rotor EMF, the range of regulation of the engine speed is doubled.

Claims (2)

1. A method of controlling the rotational speed of a dual-supply motor, in which a constant amplitude voltage is supplied to the stator winding, and an adjustable three-phase voltage directed opposite the rotor winding EMF and exceeding it is supplied to the rotor winding through a frequency converter with a DC link, voltage is measured at the conclusions of the rotor windings, determine the moments of switching the keys of the inverter of the frequency converter, commuting the keys of the inverter, set the desired engine speed, and adjust The rotation frequency is adjusted by changing the voltage supplied to the rotor winding by changing the reference signal at the input of the frequency converter, characterized in that the instantaneous values of the phase voltages at the terminals of the rotor windings are measured, the phase of the measured voltages is shifted by 150 ^° , control signals are sent to the inverter keys with a shift at the retarded angle of 150 ^o with respect to their natural switching points, after the engine acceleration to a threshold speed exceeding largest revolving frequency I stator field, change in voltage phase sequence of the stator winding of the motor and simultaneously reduce the input voltage of the frequency converter job. 2. A device for controlling the rotational speed of a dual-supply motor, comprising a frequency converter, consisting of an adjustable rectifier, the power input of which is connected through a matching transformer to the mains, and the control input to the voltage regulator, and an inverter, the power input of which is connected to the output of the rectifier, and power output to the rotor windings of the motor, the stator windings of which are designed to be connected to the mains, and the output of the pulse shaper is connected to the control input of the inverter, mained in the form of dinistras of six optocouplers, the LEDs of which are assembled in a three-phase bridge, to the output of which a resistor is connected, characterized in that a reversing contactor is inserted into the device, the coil of which is connected to the mains through the make contact of a centrifugal relay mounted on the same shaft with the motor, the switching contacts of the reversing contactor are included in two phases of the stator winding of the dual-supply motor, and the first auxiliary switching contacts of the said contactor are included in the circuit I am waiting for two phase windings of the motor rotor and two primary windings of a phase-shifting transformer assembled according to a zigzag star scheme of 150 ^° , and the second auxiliary switching contacts of the contactor are connected to the circuit between the two secondary windings of the three-phase phase-shifting transformer and the two inputs of the three-phase LED bridge, the third primary winding of the phase-shifting bridge the transformer is connected directly to the third winding of the motor rotor, and the third secondary winding is directly to the third input with etodiodnogo bridge.

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