RU2821417C1 - Device for starting asynchronous motor from diesel generator plant - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and is intended for use in self-contained power plants providing power supply to drive systems of process units, having power comparable to the source. Operation of asynchronous motor (15) start-up control device takes place in two stages. First stage of start-up starts when switching device (8) is switched on. At the same time the asynchronous motor is started with limitation of active power and consumed current to rotation frequency proportional to the specified initial value. First stage of start-up ends when the effective value of the starting current of asynchronous motor (15) falls to the specified level. From this moment the second stage of asynchronous motor (15) start-up begins. Output signal of rotation frequency setting device (20) increases from initial value with constant speed to maximum value corresponding to rated rotation frequency of asynchronous motor (15). Output signal of the voltage setting device (18) and the level of active power limitation in unit (9) increase proportionally. Smooth acceleration of asynchronous motor (15) to rated speed at rated voltage with controlled limitation of consumed active power takes place. Second stage of start-up occurs when the frequency changes ƒ and generator voltage U in accordance with the ratio U/ƒ=const by controlling the generator excitation current. Thus, frequency start-up of asynchronous motor (15) takes place at limited active power.

EFFECT: increased efficiency of power supply resource usage at asynchronous motor start-up.

1 cl, 3 dwg

Description

The present invention relates to electrical engineering and is intended for use in electric drives of industrial equipment with asynchronous motors powered by limited power sources, for example, from autonomous power plants.

Known devices for starting an asynchronous motor from a diesel generator set contain a thyristor regulator with a pulse-phase control unit connected by the output to the stator windings of an asynchronous motor, voltage and current sensors connected at the output of the thyristor alternating voltage regulator, and a setting unit (RF Patent No. 2497267, IPC N02R 1/26; RF Patent No. 2235410, IPC N02R 1/26, 2004; RF Patent No. 2596165, IPC N02R 1/26;

Known devices provide a smooth increase in voltage on the stator windings of an asynchronous motor using a thyristor regulator. In this case, the asynchronous motor starts at a reduced current compared to direct starting. When starting an asynchronous motor, the consumed current contains active and reactive components, the ratio between which, and therefore the power factor, changes. When a powerful asynchronous motor is turned on, as a result of the action of a large starting current, the voltage at the generator output decreases. At low supply voltage, the electromagnetic torque developed by the motor may not be sufficient to start the motor. The torque of an asynchronous motor is proportional to the square of the effective voltage value. For example, when the voltage decreases by 30%, the electromagnetic torque of the motor decreases by 2 times. The active power consumption reaches its maximum value at the end of the start; When the engine speed reaches a steady value, the active power takes on a value determined by the mechanical load.

When starting an asynchronous engine in an electrical network with a diesel generator set, i.e. source of limited power, the uneven nature of active power consumption causes a decrease in the efficiency of using the energy resource of the power source.

Thus, the disadvantage of known devices for controlling the start of an asynchronous motor from a diesel generator set is the low efficiency of using the energy resource of the power source.

Of the known devices, the closest to the proposed technical solution is a device for starting an asynchronous engine from a diesel generator set, containing a diesel engine with a sensor and a speed controller, the summing and subtracting inputs of the speed controller are connected to the outputs of the speed controller and speed sensor, respectively, the shaft of the diesel engine connected to the rotor of a synchronous generator, the output of which is connected through a switching device to the stator windings of the asynchronous motor, a synchronous generator excitation current regulator, connected by the output to the excitation winding of a synchronous generator, a synchronous generator current sensor and an effective current value converter connected to its output, a synchronous generator voltage sensor and an effective voltage value converter connected to its output, a voltage adjuster connected by its output to the summing input of the voltage regulator, the subtractive input of which is connected to the output of the effective voltage value converter, and the output is connected to the control input of the synchronous generator excitation current regulator (RF Patent No. 2745149. MPK N02R 1/30. Publ. 03/22/2021. Bull. No. 9).

The known device provides, when starting an asynchronous motor, a smooth increase in frequency and voltage on its stator windings by regulating the excitation of the synchronous generator. With frequency starting, the current and power consumed from the diesel generator set are limited. When starting an asynchronous motor, the consumed current contains active and reactive components, the ratio between which, and therefore the power factor, changes. The active power consumed from the source reaches its maximum value at the end of the start. The power of a diesel engine increases with increasing rotation speed. The current limit and active power levels remain constant. This causes a decrease in the efficiency of using the energy resource of the power source.

Thus, the disadvantage of the known device for controlling the start of an asynchronous motor from a diesel generator set is the low efficiency of using the energy resource of the power source.

The purpose of the proposed invention is to increase the efficiency of using the energy resource of the power source.

This goal is achieved by the fact that in the known device for starting an asynchronous engine from a diesel generator set, containing a diesel engine with a sensor and a speed controller, the summing and subtracting inputs of the speed controller are connected to the outputs of the speed controller and speed sensor, respectively, the diesel engine shaft is connected to the rotor of a synchronous generator, the output of which is connected through a switching device to the stator windings of the asynchronous motor, a synchronous generator excitation current regulator, connected by its output to the excitation winding of a synchronous generator, a synchronous generator current sensor and an effective current value converter connected to its output, a synchronous generator voltage sensor and a connected to its output is an effective voltage value converter, a voltage adjuster connected by its output to the summing input of the voltage regulator, the subtractive input of which is connected to the output of the effective voltage value converter, a threshold element, an active power limiting unit, a current limiting unit, a current regulator, an active power regulator are additionally introduced and an active power sensor, the inputs of which are connected to the outputs of the current and voltage sensors, and the output is connected to the subtracting input of the active power regulator, the output of which is connected to the input of the excitation current regulator of the synchronous motor, and the summing input is connected through the active power limiting unit to the output of the current regulator, the subtractive input of which is connected to the output of the actual current value converter, and the summing input is connected to the output of the voltage regulator through a current limiting block, the active power limiting unit and voltage and frequency setters are made with control inputs, the control input of the speed setter is connected to the output of the converter through a threshold element effective current value, the control inputs of the active power limiting unit and the voltage setter are connected to the output of the speed setter.

Compared to the closest similar technical solution, the proposed device has the following new features:

- threshold element;

- active power limiting unit;

- current limiting unit;

- current regulator;

- active power regulator;

- active power sensor;

the active power limiting unit and the voltage adjuster are made with control inputs.

Consequently, the claimed technical solution meets the “novelty” requirement.

For each of the distinctive features, a search was carried out for well-known technical solutions in the field of electrical engineering, electric drives and automation.

Known voltage regulator; current regulator; active power controller; active power sensor, in devices for starting asynchronous motors (RF Patent No. 2737953. MPK N02R 1/26. - Published 12/07/2020. Bulletin No. 34).

Active power limiting unit and voltage and frequency controllers with control inputs; the threshold element connected between the output of the actual current value converter and the control input of the frequency setter has not been found in known devices for similar purposes.

Thus, these features ensure that the claimed technical solution meets the “significant differences” requirement.

When implementing the proposed technical solution, the efficiency of using the energy resource of the power source when starting an asynchronous motor is ensured. The asynchronous motor is started by increasing the frequency and voltage of the diesel generator set from the initial minimum values. During the transient process, as a result of negative feedback on active power, the latter does not exceed the value determined by the technical characteristics of the diesel engine, and regulated during the start-up process depending on the changing characteristics of the energy source when the rotation speed of the diesel engine changes. In this case, the consumed total current, containing active and reactive components, is limited to the value permissible for an electromechanical energy converter, i.e., a synchronous generator. At the beginning of the start-up, the generator operates with a reactive current overload with low active power consumption, which ensures a high speed of electromagnetic processes in the asynchronous motor.

Consequently, the claimed technical solution meets the requirement of “positive effect”.

The essence of the proposed invention is illustrated by drawings. In fig. Figure 1 shows a diagram of a control device for starting an asynchronous motor from a diesel generator set. In fig. 1 is indicated: 1 - diesel engine; 2 - diesel engine speed controller; 3 - rotation speed sensor; 4 - synchronous generator; 5 - synchronous generator excitation current regulator; 6 - active power regulator; 7 - active power sensor; 8 - switching device; 9 - active power limitation block; 10 - current transformer; 11 - current measuring transducer; 12 - current regulator; 13 - voltage sensor; 14 - current limiting block; 15 - asynchronous motor; 16 - actual voltage value converter; 17 - voltage regulator; 18 - voltage regulator; 19 - threshold element; 20 - speed controller.

The device for starting an asynchronous engine from a diesel generator station contains a diesel engine 1 with a sensor 3 and a speed controller 2, the summing and subtracting inputs of the speed controller 2 are connected to the outputs of the speed controller 20 and the speed sensor 3, respectively, the shaft of the diesel engine 1 is connected to the rotor of the synchronous generator 4, the output of which is connected through the switching device 8 to the stator windings of the asynchronous motor 15, the excitation current regulator 5 of the synchronous generator 4 is connected by its output to the excitation winding of the synchronous generator 4, the output of the current sensor 10 of the synchronous generator 4 is connected to the input of the effective current value converter 11, the sensor voltage 13 of the synchronous generator is connected to the input of the effective voltage value converter 16, the voltage setter 18 is connected by its output to the summing input of the voltage regulator 17, the subtractive input of which is connected to the output of the effective voltage value converter 16, the inputs of the active power sensor 7 are connected to the outputs of current sensors 10 and voltage 13 of the synchronous generator 4, and the output is connected to the subtractive input of the active power regulator 6, the output of which is connected to the input of the excitation current regulator 5, and the summing input through the active power limiting unit 9 is connected to the output of the current regulator 12, the subtractive input of which is connected to the output of the converter effective current value 11, and the summing input through the current limiting unit 14 is connected to the output of the voltage regulator 17, the control input of the speed setter 20 is connected through the threshold element 19 to the output of the effective current value converter 11, the control inputs of the active power limiting unit 9 and the voltage adjuster 18 connected to the output of the speed controller 20.

The device for starting an asynchronous motor from a diesel generator station is implemented using the principle of subordinate coordinate control. The main feedback is closed by voltage on the stator winding of the asynchronous motor 15 using a series-connected voltage sensor 13 and a measuring transducer of the effective voltage value 16. The voltage at the output of the synchronous generator and, accordingly, on the stator winding of the asynchronous motor is set using a voltage setter 18. Regulator voltage 17 compares the voltage reference signal and the feedback signal acting at the output of the measuring transducer of the effective voltage value 16, and converts the error signal in accordance with the proportional (or proportional-integral) control law. The voltage setter 18 has a control input, which is connected to the output of the speed setter 20. In this case, the output signal of the voltage setter changes depending on the output signal of the speed setter 20, for example, in proportion to its output signal.

The slave current control loop of the asynchronous motor 15 is organized using a current sensor 10, an effective current value converter 11 and a current regulator 12, which implements a proportional or proportional-integral control law. The output signal of the voltage regulator 17 is supplied to the summing input of the current regulator 12 through the current limiting unit 14, in which a limit is set that corresponds to the permissible current of the power source during a set time interval.

The slave active power control circuit of the asynchronous motor 15 is organized using an active power measuring transducer 7 and an active power controller 6, which implements a proportional or proportional-integral control law. The output signal of the active power regulator 7 operates at the input of the excitation current regulator 5 of the synchronous generator 4. The output signal of the current regulator 17 is supplied to the input of the active power limiting unit 9, in which a limit is set corresponding to the active power of the power source permissible during a set time interval. The task signal for the active power controller 6 is generated at the output of the active power limitation block 9. In this case, the active power limitation level changes depending on the output signal of the speed controller 20, for example, in proportion to its output signal.

The operation of the asynchronous motor starting control device occurs in two stages as follows. At the initial moment, a signal with a logical zero level operates at the output of the threshold element 19. The first stage of the start-up begins when the switching device 8 is turned on. The controller 20 generates a control signal for the speed controller 2 of the diesel engine 1 in the form of a constant initial value, for example, corresponding to the minimum operating frequency n ₀ . The output signal of the speed setter 20 acts on the control input of the voltage setter 18, at the output of which a control signal is generated in the form of a constant initial value corresponding to the rated voltage of the synchronous generator U _n multiplied by a coefficient where n _n is the rated rotation speed of diesel engine 1. Thus, the initial value of the synchronous generator voltage is set equal to The voltage regulator 17 compares the specified voltage and the effective value of the output voltage of the synchronous generator 4 and converts the resulting difference in accordance with a proportional or proportional-integral (depending on the selected setting) control law. The output signal of the voltage regulator 17 through the current limiting unit 14 is supplied to the summing input of the current regulator 12, which compares the input signal and the effective value of the motor current, generated using a measuring transducer of the effective current value 11, and converts the resulting difference in accordance with the proportional or proportional-integral (depending on the selected setting) by the regulation law. In this case, the maximum value of the current during regulation is determined by the value of the limitation level of the current limiting unit 14.

The output signal of the current regulator 12 through the active power limiting unit 9 is supplied to the summing input of the active power regulator 6, which compares the input signal of the active power control loop and a signal proportional to the active power generated using the active power measuring transducer 7, and converts the resulting difference into in accordance with the proportional or proportional-integral (depending on the selected setting) control law. In this case, the maximum value of active power during the start-up process is determined by the value of the limitation level of the active power limitation block 9. The active power limitation level in this case changes depending on the output signal of the speed controller 20. As the rotation speed of diesel engine 1 increases, its power increases, so the limitation level in block 9 it also increases.

The output signal of the active power regulator 6 acts at the input of the excitation current regulator 5 of the synchronous generator 4. In accordance with the output signal of the active power regulator 6, the voltage is generated on the stator winding of the synchronous generator 4. In this case, the effective voltage value at the output of the synchronous generator 4 is always maintained during the start-up process in such a way that the current does not exceed the level specified by the current limiting unit 14, and the active power does not exceed the value set by the active power limiting unit 9. Thus, during the process of starting an asynchronous motor, the active power consumed from the power source does not exceed the specified value, which adjusted during the starting process depending on the power of the diesel engine 1.

The first stage of the start ends when the rotation speed of the asynchronous motor 15 reaches a specified value, proportional to the rotation speed of the synchronous generator 4, and the effective value of the starting current of the asynchronous motor 15 decreases to a specified level, for example, the nominal value. In this case, the threshold element 19 switches. At its output, a signal with a logical one level is generated, which acts on the control input of the speed setter 20. From this moment, the second stage of starting the asynchronous motor 15 begins. The output signal of the speed setter 20 increases from the initial value with constant speed to the maximum value corresponding to the rated speed of the asynchronous motor 15. At the same time, the output signal of the voltage regulator 18 and the level of active power limitation in block 9 increase proportionally. The asynchronous motor 15 smoothly accelerates to the rated speed at rated voltage with an adjustable limitation of the active active power consumed power. The second stage of starting occurs when the frequency ƒ and voltage U of the generator changes in accordance with the ratio U/ƒ=const by regulating the excitation current of the generator.

Thus, the proposed method provides frequency starting of an asynchronous motor with limited power of a diesel generator set. As a result, this ensures increased reliability of the diesel generator set when starting an asynchronous engine.

In order to confirm the positive effect achieved by using the proposed technical solution, the operation of a diesel generator set was simulated when an asynchronous motor was turned on, the power of which is commensurate with the power of the generator, using MATLAB. The following were used in the modeling:

- diesel engine 12M26G1000/5 with parameters: power 820 kW; rated frequency 1500 rpm;

- synchronous generator SG2-750/6.3-4U3 with parameters: rated power 750 kW; rated voltage 6300 V; rated current 86 A; Efficiency 94.3%; rotation speed 1500 rpm; rotor moment of inertia 44 kg⋅m ² ;

- asynchronous motor A4-450X-4MU3 with parameters: rated power 800 kW; rated voltage 6000 V; rated stator current 72.5 A; synchronous speed 1500 rpm; Efficiency 94.3%; ratio of maximum torque to nominal 2.3; starting current ratio 5.5; rotor swing moment 84 ^kg⋅m2 .

In a Simulink model compiled in accordance with the circuit shown in FIG. 1, the switching level of the threshold element 19 I _p =30 A and the initial active power limitation level P _p =80 kW are set; Initial rotation speed of the diesel engine n=750 rpm; initial linear voltage of the synchronous generator U ₀ =3 kV. The excitation voltage of the synchronous generator 4 is limited to a value equal to 2.9U _V.N , where U _V.N is the rated excitation voltage of the synchronous generator 4. The mechanical torque of the motor load depends on the angular speed Ω of the asynchronous motor 15 in accordance with the equation M _d =0, 1Ω ² .

In fig. Figure 2 shows oscillograms for the effective value of current I; effective value of line voltage U at the output of synchronous generator 4; angular velocity Ω of the asynchronous motor 15; rotation speed n of diesel engine 1. In FIG. Figure 3 shows oscillograms of the active P and reactive Q powers and the mechanical power P of the _mechanical asynchronous motor 15.

The first stage of starting the asynchronous motor 15 begins at time t ₁ =5 s. In this case, there is a sharp increase in the load current and a decrease in the output voltage of the synchronous generator 4. The angular speed of the asynchronous motor 15 increases from 0 to a value of Ω ₁ ≈75 rad/s. As a result, the asynchronous motor 15 starts at reduced voltage and frequency (time interval t ₁ -t ₂ ). During start-up, the active power is limited, so that diesel engine 1 operates without overload. At the end of the first starting stage, the current of the asynchronous motor 15 decreases and at time t ₂ ≈25 s reaches the switching level of the threshold element 19. When the latter is switched, the second starting stage begins. There is an increase in the rotational speed of the diesel engine according to a linear law and a proportional increase in the output voltage of the synchronous generator 4. As a result, the angular speed of the asynchronous motor 15 increases to the nominal value. At time t ₃ the start ends. At the end of the start (time t ₃ ≈42 s), the shaft speed of diesel engine 1 is set using controller 2 and then stabilized at the nominal level n _n =1500 rpm. The output linear voltage of the synchronous generator 4 is also maintained at a given level of 6 kV using the excitation current regulator 5.

The total start-up time is 37 s. The operation of a diesel generator set with an overcurrent of a synchronous generator occurs in the time interval t ₁ -t ₂ for 18 s. In this case, the reactive component predominates in the load current.

Consequently, the use in a known device for starting an asynchronous engine from a diesel generator set, containing a diesel engine with a sensor and a speed controller, the summing and subtracting inputs of which are connected to the outputs of the speed controller and speed sensor, respectively, the shaft of the diesel engine is connected to the rotor of a synchronous generator, the output which is connected through a switching device to the stator windings of an asynchronous motor, a synchronous generator excitation current regulator connected by its output to the excitation winding of a synchronous generator, a synchronous generator current sensor and an effective current value converter connected to its output, a synchronous generator voltage sensor and an effective current converter connected to its output voltage values, a voltage adjuster connected by its output to the summing input of the voltage regulator, a subtractive one, the input of which is connected to the output of the effective voltage value converter, additionally a threshold element, an active power limiting unit, a current limiting unit, a current regulator, an active power regulator and an active power sensor, the inputs of which are connected to the outputs of the current and voltage sensors, and the output is connected to the subtractive input of the active power regulator, the output of which is connected to the input of the excitation current regulator, and the summing input through the active power limiting unit is connected to the output of the current regulator, the subtractive input of which is connected to the output of the converter effective current value, and the summing input is connected to the output of the voltage regulator through a current limiting block, the active power limiting unit and voltage and frequency setters are made with control inputs, the control input of the speed controller is connected through a threshold element to the output of the effective current value converter, control inputs of the block Limitations of active power and voltage setter are connected to the output of the speed setter, which increases the efficiency of using the energy resource of the power source.

The use of the proposed method in industrial electric drive systems will help improve energy efficiency, reliability and quality of electrical equipment.

Claims (1)

A device for starting an asynchronous engine from a diesel generator set, containing a diesel engine with a sensor and a speed controller, the summing and subtracting inputs of the speed controller are connected to the outputs of the speed controller and the speed sensor, respectively, the shaft of the diesel engine is connected to the rotor of a synchronous generator, the output of which is connected through a switching device to the stator windings of an asynchronous motor, a synchronous generator excitation current regulator connected by an output to the excitation winding of a synchronous generator, a synchronous generator current sensor and an effective current value converter connected to its output, a synchronous generator voltage sensor and an effective voltage value converter connected to its output, a voltage adjuster connected by its output to the summing input of the voltage regulator, the subtractive input of which is connected to the output of the actual voltage value converter, characterized in that a threshold element, an active power limiting unit, a current limiting unit, a current regulator, an active power regulator and an active power sensor are additionally introduced , the inputs of which are connected to the outputs of the current and voltage sensors of the synchronous generator, and the output is connected to the subtractive input of the active power regulator, the output of which is connected to the input of the excitation current regulator, and the summing input through the active power limiting unit is connected to the output of the current regulator, the subtractive input of which is connected with the output of the effective current value converter, and the summing input is connected to the output of the voltage regulator through the current limiting block, the active power limiting unit and voltage and frequency setters are made with control inputs, the control input of the speed adjuster is connected through a threshold element to the output of the effective current value converter, The control inputs of the active power limitation block and the voltage setter are connected to the output of the speed setter.

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