Self-adaptive adjusting system of asynchronous motor under undervoltage operation

Abstract

The invention discloses a self-adaptive adjusting system of an asynchronous motor in undervoltage operation, and relates to the field of motor control. The invention aims to solve the problems that a method for processing undervoltage operation of an asynchronous motor by adopting a voltage stabilizer and an adjuster is not timely in response and lacks self-adaptive adjustment. According to the adaptive adjustment system of the asynchronous motor under the undervoltage operation, a signal acquisition unit is used for acquiring working signals of the asynchronous motor, and the working signals comprise instantaneous current, voltage and temperature rise of a stator winding of the asynchronous motor and mechanical torque of a rotor rotating shaft; the signal acquisition unit is also used for transmitting the working signal to the self-adaptive adjustment unit through the signal transmission unit; and the self-adaptive adjusting unit is used for comparing the received working signal with a rated working signal, and adjusting the input voltage of the power grid to the asynchronous motor when the received working signal exceeds a rated range.

Description

Technical Field

[0001] The invention belongs to the field of motor control. Background Art

[0002] When the local power grid composed of agricultural generators is affected by the environment, it will affect the excitation voltage of asynchronous motors in the industrial production process, and the asynchronous motors will be in undervoltage operation. In severe cases, the actual production of the enterprise will be affected. The asynchronous motor is powered by an agricultural generator set, and the three-phase AC is loaded into the three-phase symmetrical winding of the stator to realize the excitation process of the asynchronous motor, converting electrical energy into mechanical energy, so that the electrical energy provided by the power grid is converted into mechanical power on the rotor shaft; among them, the current, voltage signal and winding temperature rise carried by the stator winding, as well as the mechanical torque on the rotor shaft are the key to determine whether the motor is in undervoltage operation. When the voltage of the power grid composed of agricultural generators is insufficient, the input voltage of the asynchronous motor will be lower than the rated voltage, that is, the asynchronous motor is in an undervoltage operation state. When the load is constant, the asynchronous motor in the undervoltage operation state has insufficient excitation voltage due to the input voltage being lower than the rated voltage, resulting in a surge in current in the stator winding and copper loss, which increases the heat transfer burden of the asynchronous motor, makes the internal working state of the motor unstable, accelerates the aging of the winding insulation, greatly shortens the service life of the motor and reduces the efficiency; at the same time, the mechanical torque on the rotor shaft will be significantly reduced, and in severe cases it will cause the speed to drop or even stop, causing the company's production line to stagnate, delaying normal production progress and reducing production capacity.

[0003] At present, the existing solution for asynchronous motors under undervoltage operation is to install voltage stabilizers and regulators, which have the disadvantages of untimely response and lack of adaptive regulation design. Summary of the invention

[0004] The present invention aims to solve the problem that a method for processing undervoltage operation of an asynchronous motor using a voltage stabilizer and a regulator has untimely response and lacks adaptive regulation, and now provides an adaptive regulation system for an asynchronous motor under undervoltage operation.

[0005] The adaptive regulation system of an asynchronous motor under undervoltage operation includes: a signal acquisition unit and an adaptive regulation unit;

[0006] The signal acquisition unit is used to collect the working signal of the asynchronous motor, and the working signal includes the instantaneous current, voltage and temperature rise of the stator winding of the asynchronous motor, and the mechanical torque of the rotor shaft;

[0007] The signal acquisition unit is also used to transmit the working signal to the adaptive adjustment unit through the signal transmission unit;

[0008] The self-adaptive regulating unit is used to compare the received working signal with the rated working signal, and when the working signal exceeds the rated range, regulate the input voltage of the power grid to the asynchronous motor.

[0009] Furthermore, the signal acquisition unit includes: a current sensor, a voltage sensor, a temperature rise sensor and a torque sensor.

[0010] The current sensor, voltage sensor and temperature rise sensor are used to collect the instantaneous current, voltage and temperature rise of the stator winding of the asynchronous motor respectively;

[0011] The torque sensor is used to collect the mechanical torque of the rotor shaft of the asynchronous motor.

[0012] Further, the above-mentioned adaptive adjustment unit includes: a main control board, a third follower circuit, a second bandpass filter, a PID circuit and an AC / AC converter;

[0013] The main control board is used to receive the working signal and compare the received working signal with the rated working signal, and generate an adjustment signal when it exceeds the rated range;

[0014] The regulation signal is successively maintained by the third follower circuit and filtered by the second bandpass filter and input into the PID circuit. The PID circuit adjusts the parameters of the AC / AC converter according to the received signal, thereby adjusting the voltage connected to the asynchronous motor.

[0015] Furthermore, the main control board is also used to collect parameters of the PID circuit.

[0016] Further, the signal transmission unit comprises a first follower circuit, a first controllable amplifier circuit, a second follower circuit, a first bandpass filter and an A / D converter connected in sequence;

[0017] The working signal collected by the signal collection unit is once maintained by the first follower circuit, amplified by the first controllable amplifier circuit, maintained by the second follower circuit, filtered by the first bandpass filter and converted into a digital signal by the A / D converter;

[0018] The main control board is also used to adjust the amplification parameters of the first controllable amplification circuit.

[0019] Furthermore, the above-mentioned adaptive adjustment unit also includes a power supply, and the power supply is used to supply power to the main control board.

[0020] Furthermore, the signal acquisition unit, signal transmission unit and adaptive adjustment unit are all located in a sealed protective shell.

[0021] Furthermore, the material of the protective shell is copper.

[0022] The beneficial effects of the present invention are as follows:

[0023] First, the starting excitation source of the asynchronous motor described in the present invention is powered by the agricultural power grid and the controllable AC / AC converter connected in sequence, and the parameters in the controllable AC / AC converter are controlled by the main control board; once the asynchronous motor is detected to be in an undervoltage operation state, the main control board can promptly determine whether the asynchronous motor is undervoltage and the specific degree of undervoltage, and issue an adaptive adjustment instruction accordingly, adjust the output signal of the controllable PID circuit, adjust the voltage parameters in the AC / AC converter, and then increase the input voltage of the asynchronous motor to avoid the influence of undervoltage operation on the motor performance.

[0024] Second, the signal acquisition unit of the present invention, on the one hand, detects the current, voltage and temperature rise in the stator winding of the asynchronous motor to determine whether the asynchronous motor is in undervoltage operation and the degree of undervoltage; on the other hand, it measures the mechanical torque change curve on the rotor shaft to provide a basis for adjusting the boost degree in the AC / AC converter in the adaptive regulation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the structural diagram of the adaptive regulation system of the asynchronous motor under undervoltage operation.

[0026] Figure 2 It is the T-type equivalent circuit diagram of one phase of asynchronous motor. DETAILED DESCRIPTION

[0027] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0028] Reference Figure 1 The present embodiment is described in detail. The adaptive regulation system of the asynchronous motor under undervoltage operation described in the present embodiment includes: a signal acquisition unit, a signal transmission unit and an adaptive regulation unit.

[0029] Signal acquisition unit: used to measure the working signal of the asynchronous motor, including the instantaneous current, voltage, temperature rise of the stator winding, and the mechanical torque of the rotor shaft. Afterwards, the signal acquisition unit transmits the working signal of the asynchronous motor to the signal transmission unit.

[0030] Signal transmission unit: includes a first follower circuit, a first controllable amplifier circuit, a second follower circuit, a first bandpass filter and an A / D converter connected in sequence. The first follower circuit is used to receive the working signal collected by the signal acquisition unit, and then after amplification by the first controllable amplifier circuit, retention by the second follower circuit, and filtering by the first bandpass filter, the A / D converter completes the analog-to-digital conversion, and finally transmits the digital signal to the adaptive adjustment unit. The amplification factor of the first controllable amplifier circuit for the signal is controlled by the main control board to form a closed-loop control, measure the current signal, voltage signal, temperature rise signal of the stator winding and the mechanical torque signal on the rotor shaft, and transmit them to the main control board for the issuance of adaptive adjustment instructions.

[0031] Adaptive adjustment unit: including a main control board, a power supply for supplying power to the main control board, a third follower circuit, a second bandpass filter, a controllable PID circuit and an AC / AC converter. The main control board adopts an STM32 control chip for receiving and storing working signals from an asynchronous motor. The main control board compares the instantaneous voltage signal and current signal in the stator winding with the rated excitation voltage and current values ​​respectively, and uses the difference between the two to determine whether the motor is in undervoltage operation at this time; according to the mechanical torque on the rotor shaft, the electromagnetic power is calculated to determine the degree of undervoltage operation of the motor. If it is in undervoltage operation, an adaptive adjustment signal instruction is issued.

[0032] The controllable PID circuit is connected to the main control board, and the parameters in the controllable PID circuit are controlled by the main control board. The input side of the AC / AC converter is respectively connected to the agricultural power grid and the output side of the controllable PID circuit, and the output side of the AC / AC converter is connected to the three-phase winding of the stator; the parameters in the AC / AC converter are controlled by the output signal of the controllable PID circuit.

[0033] In this embodiment, the voltage signal in the agricultural power grid is input into the three-phase winding in the asynchronous motor junction box via an AC / AC converter. One side of the input end of the signal acquisition unit is connected to the three-phase winding in the stator slot of the asynchronous motor, and the other side is connected to the output end of the rotor shaft mechanical torque measuring instrument.

[0034] Once the main control board module analyzes the undervoltage situation and degree of the asynchronous motor, it adjusts the voltage parameters in the AC / AC converter circuit through the third follower circuit, the second bandpass filter, and the PID circuit in sequence, thereby increasing the input voltage of the agricultural power grid to the asynchronous motor. At the same time, the main control board monitors the signal collected by the signal acquisition unit of the asynchronous motor in real time to form a closed-loop control, so that the voltage at the input end of the motor increases, the instantaneous voltage in the winding increases, the instantaneous current decreases, and the mechanical torque on the shaft increases, thereby achieving more precise adaptive adjustment and control.

[0035] The signal acquisition unit, signal transmission unit and adaptive adjustment unit are all placed in a protective shell made of a sealed metal copper plate, which isolates the interference of electromagnetic signals in the working environment of the motor, realizes accurate monitoring of the motor status signal and rapid issuance of adaptive adjustment instructions.

[0036] Working principle:

[0037] The agricultural power grid composed of multiple groups of generators supplies power to the three-phase winding of the asynchronous motor through the AC / AC converter. At this time, the electromagnetic induction in the three-phase winding of the stator induces an electromotive force and a rotating magnetic field on the rotor. Under the action of the electromagnetic force, the rotor rotates at a certain numerical speed. After the motor runs smoothly, a constant load is added to the shaft. The instantaneous current, voltage, temperature rise in the three-phase winding of the stator and the mechanical torque signal on the shaft are detected by the current sensor, voltage sensor, temperature rise sensor and torque sensor respectively. The signals are sent to the main control board through the signal acquisition unit and the signal transmission unit for comparison and analysis. If it is detected that the motor is in undervoltage operation, the main control board issues an adaptive adjustment instruction, which is input into the AC / AC converter through the voltage follower circuit, the bandpass filter circuit and the PID circuit. The voltage parameter conversion value in the AC / AC converter is realized by changing the parameters in the PID circuit to adjust the input voltage of the motor, adjust the internal electromechanical energy conversion of the motor, and reduce the influence of insufficient input voltage on the life and performance of the motor. At the same time, the main control board can store and display the change curve of the motor torque with load.

[0038] Theoretical basis:

[0039] like Figure 2 As shown, the terminal voltage U1 represents the input phase voltage of the induction motor, which is generated by the agricultural power grid through the AC / AC converter circuit and input to the stator three-phase winding. R1 is the resistance of one phase winding on the stator side, X 1σ is the stator side leakage reactance, I1 is the input phase current in one phase winding of the stator, R m is the excitation winding, X m is the magnetizing reactance, I m is the excitation current, R2 is the resistance of one phase winding on the rotor side, X 2σ is the rotor side leakage reactance, I2 is the rotor side phase current, is the load resistance of one phase on the shaft. j is a vector with direction, E1 is the induced electromotive force on the stator side, E2 is the value of the induced electromotive force on the rotor side converted to the stator side, and the superscript "'" indicates the converted value of the parameter converted to the stator side.

[0040] The voltage equations of the stator and rotor of an asynchronous motor are as follows:

[0041]

[0042] Depend on Figure 2From the equivalent circuit of the asynchronous motor, it can be seen that the input power P1 supplied by the power supply to the asynchronous motor is:

[0043]

[0044] in, is the power factor angle of the motor, indicating the phase angle that U1 on the stator side leads I1; m1 is the number of phases of the motor, generally a three-phase induction motor, in which case m1 is 3.

[0045] Part of the input power P1 is consumed by the stator winding resistance R1 and converted into stator winding copper loss P Cu1 :

[0046]

[0047] Another part of the input power P1 is consumed by eddy current and hysteresis loss in the stator core. The alternating frequency of the magnetic field in the rotor core is sf1. Since the slip rate s is very small, the frequency of magnetic field change in the rotor is very low, so the rotor core loss can be ignored. The total iron loss corresponds to R in the equivalent circuit. m Loss on:

[0048]

[0049] Input power minus stator winding copper loss P Cu1 and iron loss P Fe After that, the remaining power is all transmitted to the rotor through the air gap by electromagnetic induction, which is called electromagnetic power P e , so we have:

[0050] P e =P1-P Cu1 -P Fe .

[0051] From the equivalent circuit, we can see that:

[0052]

[0053] in, is the power factor angle of the motor, indicating the phase angle at which the rotor side E' leads I2'.

[0054] Electromagnetic power P e Part of it is consumed in the rotor resistance and converted into heat energy, which is called rotor copper loss P Cu2 , the formula is

[0055]

[0056] Among them, m2 is the number of phases of the rotor.

[0057] The rest of the power is converted into mechanical energy, which is called total mechanical power P Ω , which corresponds to the power consumed in the additional resistance (1-s)R′2 / s in the equivalent stationary rotor:

[0058]

[0059] Total mechanical power P Ω Part of the power is consumed to overcome the mechanical loss P caused by bearing friction and wind friction resistance. Φ , and part of the power is consumed to overcome the additional loss P Δ Corresponding braking torque. From the total mechanical power P Ω Deduct P Φ and P Δ After the two parts are lost, the output power P2 is obtained, that is,

[0060] P2=P Ω -P Φ -P Δ .

[0061] The asynchronous motor generates electromagnetic torque through the action of rotor current and magnetic field. The electromagnetic torque overcomes the resistance torque of the mechanical load to perform work, output mechanical power, and thus convert electrical energy into mechanical energy.

[0062]

[0063] T2=T e -T0,

[0064]

[0065] Among them, T e is the electromagnetic torque, T0 is the no-load torque corresponding to the mechanical loss and additional loss, T2 is the output torque, n is the rotor shaft speed, n s is the synchronous electromagnetic speed, Ω s is the synchronous mechanical angular velocity, and Ω is the mechanical angular velocity.

[0066] In summary, the adaptive regulation system of an asynchronous motor under undervoltage operation of the present invention is to solve the problem that the asynchronous motor under undervoltage operation has an unstable internal working state due to insufficient excitation voltage, serious heating of the motor, insulation aging, shaft failure, shortened service life, and equipment downtime causing economic losses to the factory. The adaptive regulation system of an asynchronous motor under undervoltage operation of the present invention comprises: a signal acquisition unit, a signal transmission unit and an adaptive regulation unit. On the one hand, the winding temperature rise, instantaneous current and instantaneous voltage are detected from the stator winding, and the torque fluctuation of the rotor shaft is measured from the rotor side. The collected signal is transmitted to the main control board circuit for processing through the first follower circuit, the first controllable amplifier circuit, the second follower circuit, the first bandpass filter, and the A / D conversion to obtain an electrical signal representing that the motor is in undervoltage operation; on the other hand, if the main control board detects that the motor is in undervoltage operation, an adaptive adjustment command signal is issued according to the degree of undervoltage in multiple places of the motor, and the voltage in the three-phase winding of the asynchronous motor is changed through the third follower circuit, the second bandpass filter, the PID circuit, and the AC / AC converter, so as to realize the adaptive adjustment function of the motor under undervoltage operation and avoid the motor shutdown failure caused by undervoltage operation.

[0067] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. An adaptive regulation system for an asynchronous motor under undervoltage operation, characterized in that: include: Signal acquisition unit and adaptive adjustment unit; The signal acquisition unit is used to collect the working signal of the asynchronous motor, and the working signal includes the instantaneous current, voltage and temperature rise of the stator winding of the asynchronous motor, and the mechanical torque of the rotor shaft; The signal acquisition unit is also used to transmit the working signal to the adaptive adjustment unit through the signal transmission unit; The self-adaptive regulating unit is used to compare the received working signal with the rated working signal, and when the working signal exceeds the rated range, regulate the input voltage of the power grid to the asynchronous motor.

2. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 1, characterized in that: The signal acquisition unit includes: a current sensor, a voltage sensor, a temperature rise sensor and a torque sensor. The current sensor, voltage sensor and temperature rise sensor are used to collect the instantaneous current, voltage and temperature rise of the stator winding of the asynchronous motor respectively; The torque sensor is used to collect the mechanical torque of the rotor shaft of the asynchronous motor.

3. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 1, characterized in that: The adaptive adjustment unit comprises: a main control board, a third follower circuit, a second band-pass filter, a PID circuit and an AC / AC converter; The main control board is used to receive the working signal and compare the received working signal with the rated working signal, and generate an adjustment signal when it exceeds the rated range; The regulation signal is successively maintained by the third follower circuit and filtered by the second bandpass filter and input into the PID circuit. The PID circuit adjusts the parameters of the AC / AC converter according to the received signal, thereby adjusting the voltage connected to the asynchronous motor.

4. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 3, characterized in that: The main control board is also used to collect parameters of the PID circuit.

5. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 3 or 4, characterized in that: The signal transmission unit comprises a first follower circuit, a first controllable amplifier circuit, a second follower circuit, a first bandpass filter and an A / D converter connected in sequence; The working signal collected by the signal collection unit is once maintained by the first follower circuit, amplified by the first controllable amplifier circuit, maintained by the second follower circuit, filtered by the first bandpass filter and converted into a digital signal by the A / D converter; The main control board is also used to adjust the amplification parameters of the first controllable amplification circuit.

6. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 5, characterized in that: The adaptive adjustment unit also includes a power supply, and the power supply is used to supply power to the main control board.

7. The adaptive regulation system of an asynchronous motor under undervoltage operation according to claim 6, characterized in that: The signal acquisition unit, the signal transmission unit and the adaptive adjustment unit are all located in a sealed protective shell.

8. The adaptive regulation system for an asynchronous motor under undervoltage operation according to claim 7, characterized in that: The material of the protective shell is copper.

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