RU2326480C1 - Method of control and provision of survivability of three phase induction motor - Google Patents

Abstract

FIELD: electricity, electric equipment.

SUBSTANCE: invention is related to the sphere of electric equipment and may be used in widely regulated induction electric drives. Technical result is provision of survivability of three-phase induction motor in case of emergency disconnection of one of three phases by preservation of circular rotating field. The method of control and provision of survivability of three-phase induction motor, the phase windings of motor stator are supplied from three-phase frequency transducer, which operates in the mode of current source, which is realized by regulation of phase currents, which provide their proportionality to setting signals for currents, which are shaped at the outlet of speed regulator, at the inputs of which the setting signal of rotation frequency is sent as well as the current value of motor shaft rotation frequency. At the outlet of speed regulator, three-phase systems of setting signals for phase currents are obtained. Simultaneously with above mentioned, the analysis of motor phase currents is continuously done in every interval of width-pulse modulation and in case failure is detected in one of the motor phases, the instant values of currents are corrected in two remaining phases of induction motor by values for anticipatory and lagging phase of current vector, which are specified in invention formula.

EFFECT: provision of three-phase induction motor survivability in case of emergency disconnection of one phase.

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Description

The invention relates to electrical engineering and can be used in widely adjustable asynchronous electric drives.

A known method of ensuring the survivability of five- or seven-phase asynchronous motors with vector control from a frequency converter (Disturbance-free operation of a multiphase current-regulated motor drive with an opened phase / Fu Jen-Ren, Lipo Thomas A. // IEEE Trans. Ind. Appl. - 1994. - 30, No. 5. - P.1267-1274), in which, when one of the phases is broken, the corresponding frequency combination is set in the frequency converter to maintain the motor torque without ripples, while eliminating the neutral wire, t. to. the presence of a zero sequence of currents, unlike a 3-phase asynchronous motor, will be optional.

The disadvantage of this method is the limited scope for multiphase induction motors, which does not allow the use of the proposed method with a three-phase motor design.

There is a method of ensuring the survivability of a three-phase asynchronous motor for driving an escalator (JP Patent No. 3293289, IPC В66В 23/02, publ. 24.12.1991), in which performance is restored in the event of a power failure in the frequency converter: rectifier - inverter. Survivability is provided by diagnostics, followed by disconnecting the motor power from the frequency converter and switching it directly to a three-phase AC network.

The disadvantage of this method is to reduce the uniformity of movement of the escalator when the frequency converter is switched off due to an abrupt decrease or increase in the frequency of rotation of the motor shaft depending on the degree of congestion of the escalator and, as a result, the limited applicability of this method, as well as the inability to operate this electric drive when the motor phase breaks directly supplying the stator winding.

A known method of ensuring the survivability of an asynchronous electric drive (Fault mode single-phase operation of a variable frequency induction motor drive and improvement of pulsating torque characteristics. / Kastha Debaprasad, Bose Bimal K. // IEEE Trans. Ind. Electron. - 1994. - 41, No. 4. - S.426-433), in which, upon phase failure or disconnection due to a malfunction, voltage harmonics are introduced to neutralize the second and other harmonics of the ripple of the moment and shift the ripple frequency of the moment to a higher range of the spectrum, which makes it possible to compensate for the ripple of the moment due to the moment of inertia of the engine. To control the electric drive in two-phase mode, the optimal voltage / frequency ratio U / f is introduced into the frequency converter to obtain the maximum torque / current ratio and reduce torque ripples, which ensures acceptable operation with the motor shaft speed control.

The disadvantage of this method is the impossibility of applying the proposed technical solution in the case of a deeply adjustable electric drive, especially in the low speed range.

A known method of controlling an electric drive (RF patent No. 2109397, IPC 6 Н02Р 5/408, publ. 04.20.1998), selected as a prototype, which consists in the fact that the phase windings of the motor stator are powered from a three-phase thyristor frequency converter with direct connection and natural switching operating in the mode of a current source, which is implemented by regulating the phase currents, ensuring their proportionality to the current reference signals generated at the output of the speed controller, to the inputs of which a speed reference signal is supplied Nia and phase motor EMF. The speed controller master oscillator is controlled by a frequency reference signal, generating at its output three-phase systems of reference signals for basic currents and basic EMFs, which are respectively in quadrature, whose modules are determined by the corresponding reference signals. The reference signal to the base EMF module is determined by multiplying the reference signal of the base current module by the frequency reference signal, the reference signal to the base current module is determined by summing the reference signal to the base current module in idle mode and the signal increment signal module, which is obtained by integrating the difference the reference signal to the base EMF of this phase and the EMF of the corresponding phase of the engine. The reference signal for the current of each phase is determined by summing the reference signal for the base current of this phase and the corresponding signal signal increment of the reference signal for current.

The disadvantage of this method is the inability to ensure the survivability of the electric drive in the event of a break in one of the phases of the motor and a failure in one of the cells of the frequency converter.

The objective of the invention is to ensure the survivability of a three-phase asynchronous motor during emergency shutdown of one of the phases by maintaining a circular rotating field.

The problem is solved due to the fact that in the method of controlling and ensuring the survivability of a three-phase asynchronous motor, as in the prototype, the phase windings of the stator of the motor are powered from a three-phase frequency converter operating in the mode of a current source, which is implemented by adjusting the phase currents, ensuring their proportionality to the signals reference for currents generated at the output of the speed controller, the inputs of which supply a signal for setting the speed, and at its output receive three-phase signal systems Niya on the phase currents.

According to the claimed method, simultaneously with the foregoing, the rotational speed of the motor shaft is continuously determined and the phase currents of the motor are analyzed at each interval of pulse-width modulation, and if a failure is detected in one of the motor phases, the instantaneous currents in the two remaining phases of the induction motor are corrected according to the expressions for the leading phase current vectors:

for the lagging phase of the current vector:

where I _ω is the amplitude value of the generated phase currents, A;

σ is the number of binary bits of the output code of the digital signal obtained by integrating the signal from the speed sensor;

a, b, c - three bits of failure of each phase;

- инверсные значения а, b, с, d;

- inverse values of a, b, c, d;

α is the value of the current binary code of the digital signal obtained by integrating the signal from the speed sensor;

d is the value of the bit calculated by the logical expression d = a∪b∪c (∪ is the logical OR operation); if d = 1, then this indicates a failure in one of the engine phases.

The task is achieved in that if a failure is detected in one of the engine phases, an operation recovery algorithm is included, in which the instantaneous values of the currents in the two remaining phases of the induction motor are corrected, i.e. change the phase rotation order and phase angle between the remaining phases from 2π / 3 to π / 2 (1) - (6). Thus, the proposed solution allows to maintain the circular rotating field of the engine and the direction of rotation of the motor shaft with an extended control range, as well as to provide a 100% probability of starting in a given direction. The response time of the microprocessor control system when switching the recovery algorithm from three-phase to two-phase mode is equal to the time interval of the pulse-width modulation in the absence of additional hardware costs to support the recovery algorithm.

Figure 1 presents a functional diagram of a microcontroller control system for a three-phase asynchronous motor.

Figure 2 presents the timing diagrams of transients of the stator currents in phases A, B, C: I _A , I _B , I _C and the motor shaft rotation frequency ω when switching from a working 3-phase to emergency 2-phase operation for uncontrolled emergency.

Figure 3 presents the timing diagrams of transients of the stator currents in phases A, B, C: I _A , I _B , I _C and the motor shaft speed ω when switching from a working 3-phase to emergency 2-phase operation at activated recovery algorithm.

The proposed method is implemented using the following circuit shown in figure 1, where the induction motor 1 (HELL) through current sensors 2 (DT1), 3 (DT2), 4 (DT3) is connected to the converter cells 5 (ПЯ1), 6 (ПЯ2 ) and 7 (ПЯ3) of the three-phase frequency converter, to which the diagnostic unit 8 (DB) is connected, connected to the microcontroller 9 (MK). The outputs of the current sensors 2 (DT1), 3 (DT2), 4 (DTZ) are connected to the microcontroller 9 (MK). A speed sensor 10 (DS) is installed on the shaft of the induction motor 1 (HELL), the output of which is connected to the microcontroller 9 (MK). The setpoint of the rotational speed of the motor shaft 11 (HF) is connected to the microcontroller 9 (MK), which is also connected to the converter cells 5 (ПЯ1), 6 (ПЯ2), 7 (ПЯ3).

As an asynchronous motor 1 (AM), you can choose any three-phase asynchronous motor with isolated phases, i.e. the beginning and end of each stator winding are displayed in a terminal box, for example ADM63V4U3. As current sensors 2 (DT1), 3 (DT2), 4 (DT3) standard sensors with galvanic isolation can be used, for example LEM modules of type LA 25-NP. Speed sensor 10 (DS) can be of any type with an analog or digital output, for example BE 178A. As microcontroller 9 (MK), a single-board microcontroller type AT89C2051 with a clock frequency of 4 MHz can be selected. As converter cells 5 (ПЯ1), 6 (ПЯ2), 7 (ПЯ3) of a three-phase frequency converter, an inverter made according to a bridge or half-bridge circuit is used. The speed controller 11 (ZHV) can be made in the form of a block that generates an analog or digital reference signal. An embodiment of the diagnostic unit 8 (DB) is described in [Odnokopylov G.I. Transducer cell state sensor // IV International Scientific and Technical Conference "Microprocessor, analog and digital systems: design and circuitry, theory and application issues", Novocherkassk: Publishing House of SRSTU 2004. - 70 pp.].

To check the control method and ensure the survivability of a three-phase asynchronous motor, a mathematical model was used [RF certificate on registration of the computer No. 20055612119 "Program for the calculation of transients of an induction motor with an electromagnetic brake device"]. The input value of the electric drive is the signal from the speed control unit 11 (HF), which is supplied to the microcontroller 9 (MK). The phase currents of the motor, determined using current sensors 2 (DT1), 3 (DT2), 4 (DT3), and the frequency of rotation of the motor shaft, which is determined using the speed sensor 10 (DC), are supplied to the current regulators and speed controller, respectively, programmed in the microcontroller 9 (MK), in which current tasks for each phase of the motor are generated, which enter the converter cells 5 (ПЯ1), 6 (ПЯ2), 7 (ПЯ3) of a three-phase frequency converter. Diagnostic unit 8 (DB) analyzes the state of the converter cells 5 (ПЯ1), 6 (ПЯ2), 7 (ПЯ3) on each pulse-width modulation interval and generates three failure bits a, b, c, which make up the drive status word, coming to the microcontroller 9 (MK). If a failure is detected either in one of the phases of the motor, or in one of the cells of the frequency converter in the microcontroller 9 (MK), a recovery algorithm is included in which the instantaneous values of the phase currents of the asynchronous motor 1 (AM) are corrected for the leading phase of the current vector according to the expressions (1 ), (2), (3), and for the lagging phase of the current vector according to expressions (4), (5), (6).

The timing diagrams of transients (figure 2, 3) shows the operation of an MTF 311-6 induction motor with a rated load moment (M _n = 111N · m) on the shaft when switching from a working 3-phase to emergency 2-phase mode work in case of failure in phase "A" at a time equal to t = 0 s. In an uncontrolled emergency, as can be seen from figure 2, the current in the failed phase ("A") became equal to zero, and the currents in the remaining phases "B" and "C" after the electromagnetic transient t = 0.05 s became the same , as in the 3-phase mode with a phase angle between them equal to 2π / 3. In this case, the rotational speed of the engine shaft drops to zero in time t = 0.375 s followed by the rollover of the engine, i.e. an induction motor does not support the survivability property.

With the activated recovery algorithm (Fig. 3), the currents in the two remaining phases “B” and “C” after the electromagnetic transient t = 0.05 s have the same amplitude in amplitude as in the 3-phase mode, but with reverse rotation and a phase angle between them equal to π / 2, which is determined by the restoration algorithm (2) and (3) to maintain a circular rotating field of the engine. After that, the engine shaft speed drops to the level of 30% relative to the three-phase operation. The engine continues to run, maintaining the rated load on the shaft. That is, the use of the proposed method provides the survivability of a three-phase asynchronous motor during emergency phase shutdown.

The proposed technical solution allows, in the event of a failure in one of the engine phases, to ensure the rotation direction, a circular rotating field and a 100% probability of starting in a given direction with an extended control range and a specific reaction time of the microprocessor control system when switching the recovery algorithm from three-phase to two-phase mode, equal to the time interval of the pulse width modulation in the absence of additional hardware costs to support the slave recovery algorithm petitiveness.

Claims (1)

The method of controlling and ensuring the survivability of a three-phase asynchronous motor, namely, that the phase windings of the stator of the motor are powered from a three-phase frequency converter operating in the current source mode, which is implemented by regulating the phase currents, which ensures their proportionality to the reference signals for currents generated at the output of the speed controller, at the inputs of which a speed reference signal is supplied, and at its output three-phase systems of reference signals for phase currents are obtained, characterized in that one temporarily with the foregoing, the rotational speed of the motor shaft is continuously determined and the phase currents of the motor are analyzed at each interval of pulse-width modulation, and if a failure is detected in one of the motor phases, the instantaneous currents in the two remaining phases of the induction motor are corrected by the expressions for the leading phase of the current vector:

for the lagging phase of the current vector:

where I _ω is the amplitude value of the generated phase currents, A; σ is the number of binary bits of the output code of the digital signal obtained by integrating the signal from the speed sensor; a, b, c - three bits of failure of each phase;

- inverse values of a, b, c, d; α is the value of the current binary code of the digital signal obtained by integrating the signal from the speed sensor; d is the value of the bit calculated by the logical expression d = a∪b∪c (∪ is the logical OR operation); if d = 1, then this indicates a failure in one of the engine phases.

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