RU2543970C1 - Device for control over digital frequency-adjustable electrical drive - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed device comprises controlled frequency inverter, intensity master, motor e.m.f. and voltage error sensors, motor e.m.f. controller and frequency controller. Additionally introduced are current transducer, function generator, motor e.m.f. feedback signal time sampling unit. Thinker defines the sign of motor e.m.f. signal current increment. Correction unit corrects motor acceleration and deceleration time subject to aforesaid sign. Motor acceleration and deceleration is controlled by time sampling of motor e.m.f. feedback signal time sampling, measurement of instantaneous amplitudes of quantised pulses and determination of sign of motor quantised e.m.f. signal current increments. Second differences of instantaneous amplitudes for every three quantised serial pulses are calculated. Acceleration and deceleration times are corrected subject to the sign of said second differences.

EFFECT: optimised acceleration of drive without overload at inverter power components.

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Description

Technical field

The invention relates to the field of electrical engineering and can be used in digital automated AC electric drives with frequency converters.

State of the art

A device for controlling a frequency-controlled electric drive according to the patent of the Russian Federation No. 1836802.

The device comprises a frequency converter composed of series-connected units: an adjustable rectifier, a filter, an inverter. The control input of the rectifier is connected to the output of the control unit of the rectifier, the control input of the inverter is connected to the output of the control unit of the inverter, the input of which is connected to the output of the master frequency generator. The outputs of the voltage and current sensors of the motor are connected to the inputs of the motor EMF determination unit, the output of which is connected to one of the inputs of the comparison unit, the other input of which is connected to the output of the motor EMF restriction unit. The input of the EMF restriction block is connected to the output of the intensity adjuster, the input connected to the output of the comparison unit. The output of the EMF limiting unit is connected to the input of the rectifier control unit and one of the inputs of the engine EMF error sensor, the other input of which is connected to the output of the EMF detection unit, and the output is connected to one of the inputs of the summing amplifier, the other input of which is connected to the output of the EMF limiting unit. The phases of the stator winding of the motor are connected to the inverter outputs.

The technical solution is aimed at ensuring a constant relationship between the current values of the EMF and the frequency of the stator field (EMF) of the motor during overloads in static and dynamic modes, i.e. when current limiting starts to work to prevent the motor from “tipping over”.

The disadvantage is that maintaining a constant relationship between the current values of the EMF and the frequency of the stator field (EMF) of the motor is provided only in overload mode during current limiting operation, and not in all modes of operation of the electric drive, which narrows its functionality.

The closest technical solution, taken as a prototype, is set forth in the patent of the Russian Federation No. 2331152.

According to the patent, a device for controlling a frequency-controlled electric drive comprises a frequency converter composed of series-connected unregulated rectifier, filter and inverter, the output of which is connected through a voltage sensor to the stator of an induction motor. To control the inverter, an inverter control unit is used, the output of which is connected to the control input of the inverter. The device also includes an intensity adjuster that determines the set value of the motor EMF, an EMF error sensor that detects an EMF control error, and a comparison unit connected at the output to the intensity adjuster, and from one of its inputs to an EMF error sensor.

In addition, the device contains a motor EMF controller with two inputs, a frequency controller of the stator field of the motor with three inputs, a functional converter with three inputs.

The inverter control unit has two inputs, the first of which is connected to the output of the frequency controller of the stator field, and the second to the output of the motor EMF controller. The output of the intensity adjuster is connected to one of the inputs of the EMF error sensor and the connection point of the second inputs: the frequency controller of the stator field of the motor, the motor EMF regulator, and the functional converter. The output of the EMF error sensor is connected to the third input of the frequency controller of the stator field of the motor, and the second input of the EMF error sensor is connected to the first input of the motor EMF controller and the output of the functional converter, the third input of which is connected to the motor voltage sensor.

The absolute rotor slider of the engine rotor sets the amount of slip that determines the moment of the engine in the starting braking modes of its operation. The output of the absolute slip master is connected to the second input of the comparison unit and to the first inputs of the frequency controller and the functional converter.

The technical solution is aimed at ensuring compliance at any time with the current value of the frequency of the stator field of the motor to the current value of the motor EMF in all modes of operation.

Optimization of the speed of the acceleration and braking processes is carried out by acting on the signal intensity setter of the comparison unit, depending on the ratio of the signals of the EMF error sensor and the absolute slip setter.

The disadvantage is that the device optimizes the speed of the acceleration and braking processes only in the analog control system of the electric drive and cannot be used in a digital control system.

The use of microprocessor technology when creating a device for controlling a frequency-controlled electric drive will not only significantly reduce the dimensions of the device, but also increase the flexibility of controlling the electric drive in terms of changing its operation algorithms and technical characteristics by changing the software of the microcontroller accordingly. However, in this case, the issue of optimizing the speed of acceleration and braking of the electric drive must be solved in a different way compared to the analog device of the prototype.

Therefore, the aim of the invention is to provide a device for controlling a digital frequency-controlled electric drive with reduced dimensions and increased flexibility of controlling the electric drive, which optimizes the speed of acceleration and braking of the electric drive without “tipping” the motor during acceleration and without overvoltage on the power elements of the frequency converter during braking.

Disclosure of invention

The proposed device for controlling a digital frequency-controlled electric drive contains a frequency converter composed of series-connected elements: a constant voltage source, a filter and an inverter, the output of which is connected through a voltage sensor to the stator of an induction motor. To control the inverter, an inverter control unit is used, the output connected to the inverter input.

To control the frequency of the stator field of the motor, a frequency regulator is used, the output of which is connected to the first input of the control unit. To regulate the motor EMF, an EMF regulator is used, the output connected to the second input of the inverter control unit. To set the acceleration speed and braking speed of the electric drive, an intensity adjuster is used, the output is connected to the first input of the EMF error sensor, the first input of the frequency controller and the first input of the motor EMF controller. The functional converter is used to determine the motor EMF from the signals of the voltage sensor and an additional current sensor inserted into the device, the first input of the functional converter connected to the output of the voltage sensor, and the second input to the output of the current sensor, and the output connected to the second input of the motor EMF controller and the second EMF error sensor input. The essence of the invention lies in the fact that in the device for controlling an electric drive (for example, with an induction motor), adjustable in frequency, which contains a frequency converter, an inverter control unit, EMF and frequency regulators of the stator field of the motor, EMF error sensor, elements are introduced that allow optimization on the speed of acceleration and braking of the engine.

This is a current sensor, a functional converter, which determines the feedback signal from the motor EMF, the time quantization block of the feedback signal from the motor EMF, the solving block and the block for correcting the acceleration time and engine braking time using the signals of the voltage and current sensors.

In this case, the functional converter is connected by the first input to the output of the voltage sensor, the second input to the output of the current sensor, and the output to the second input of the motor EMF error sensor, to the second input of the motor EMF controller and to the input of the quantization unit, the output of which is connected to the input of the deciding unit , the output of the acceleration time and engine braking time correction unit connected to the input of the correction unit, the output of which is connected to the input of the intensity adjuster.

Due to the fact that the acceleration and deceleration of the digital frequency-controlled electric drive are controlled by continuously quantizing the feedback signal by EMF by the quantization unit, continuously measuring the instantaneous values of the amplitudes of the quantized pulses, continuously determining the sign of the current increment of the amplitudes of the quantized pulses by calculating the second differences of the instantaneous amplitudes for every three consecutive quantized pulses using a decision block and continuously correction of the acceleration time and the braking time by appropriate action of the intensity adjuster, depending on the sign of the second differences of the instantaneous values of the amplitudes of the quantized pulses, the acceleration of the electric drive without “tipping” of the asynchronous motor and the braking of the electric drive without overvoltage on the inverter power elements are optimized for speed.

Brief Description of the Graphic Figure

Figure 1 presents a block diagram of a device for controlling a digital frequency-controlled electric drive. The numbers indicate:

1 - constant voltage source,

2 - filter

3 - inverter,

4 - voltage sensor,

5 - current sensor,

6 - induction motor,

7 - inverter control unit,

8 - motor EMF regulator,

9 - motor frequency controller,

10 - functional converter

11 - engine EMF error sensor,

12 - intensity adjuster,

13 is a block of time quantization of the feedback signal of the EMF of the engine,

14 - a crucial unit,

15 - block correction of acceleration time and engine braking time.

The implementation of the invention

The proposed device for controlling a digital frequency-controlled electric drive (figure 1) contains a frequency converter composed of series-connected elements: a constant voltage source 1, an inductive-capacitive filter 2 and an inverter 3, the output of which is connected through the voltage sensors 4 and current 5 to the phases stator winding of an induction motor 6. The control unit 7 of the inverter is connected at its output to the control input of the inverter 3, and at its two inputs, respectively, to the output of the regulator 8 of the motor EMF controller 9 to the output frequency of the motor stator field. The output intensity adjuster 12 is connected to the first input of the motor EMF controller 8, the first input of the motor EMF sensor 11 and the first input of the motor stator field frequency controller 9, the second input of the motor stator field frequency regulator is connected to the output of the motor EMF sensor 11. The functional Converter 10 inputs connected to the outputs of the voltage sensor 4 and the current sensor 5, and the output to the input of the quantization unit 13, as well as the second inputs of the regulator 8 of the EMF of the engine and the sensor 11 of the error of the EMF of the engine. The output quantization unit 13 is connected to the input of the decision unit 14, the output of which is connected to the input of the acceleration time and braking time correction unit 15, the output associated with the input of the intensity adjuster 12.

The following may be selected as specific elements of the described flowchart:

1 (constant voltage source - unregulated rectifier) - three-phase rectifier module type M6D-63-400, 63A, 400V;

2 (filter) - a DC inductor with an inductance of 1 mH, a SHL core of 20 × 25, an air gap of 1.25 mm per current 25A; K50-77-250 V-4700 uF electrolytic capacitor;

3 (inverter) - three-phase inverter module SEMIX101GDO66HDS (Germany), 140A, 600V;

4 (voltage sensor) - type LV25-P / SP3;

5 (current sensor) - type LA55-P / SP21;

7 (control unit) - driver SKHI71 (Germany);

10 (functional converter) - operational amplifier type 140UD7VK;

7, 8, 9, 13, 14, 15 - devices can be performed on a microcontroller type ST10F276Z5T3 (USA), ST10 series;

12 (intensity adjuster) - integrator on the amplifier type 140UD7VK;

6 (asynchronous motor) - an asynchronous motor with a squirrel-cage rotor with a capacity of 2 kW, 12000 rpm.

The device operates as follows:

поступает на первый вход регулятора 8 ЭДС двигателя. Этот же сигнал в качестве задания частоты поля статора двигателя

поступает на первый вход регулятора 9 частоты поля статора двигателя. На второй вход регулятора 8 ЭДС двигателя поступает сигнал текущего значения ЭДС двигателя e₁ в качестве сигнала обратной связи по ЭДС с выхода функционального преобразователя 10. Регулятор 8 ЭДС двигателя является ИП-регулятором, т.е. имеет астатизм первого порядка. Он реализует функцию управления в виде:From the output of the setter 12 of the intensity of the reference signal EMF engine

enters the first input of the regulator 8 EMF engine. The same signal as the reference frequency of the stator field of the motor

arrives at the first input of the controller 9 of the frequency of the stator field of the engine. The signal of the current value of the motor EMF e ₁ is fed to the second input of the motor EMF controller 8 as an EMF feedback signal from the output of the functional converter 10. The motor EMF controller 8 is an IP controller, i.e. has astatism of the first order. It implements a control function in the form of:

where U _y is the control signal for the magnitude of the motor EMF coming from the output of the regulator 8 of the motor EMF to the second input of the inverter control unit 7;

T _E is the time constant of the integral component of the signal U _y ;

K _E - transmission coefficient proportional to the signal component U _у .

и e₁, и поэтому корректно соотношение

. Однако в динамических режимах электропривода величиной Δe₁ пренебречь нельзя. Текущее значение ЭДС (e₁) определяется функциональным преобразователем 10 из текущего значения напряжения U₁ двигателя, поступающего с выхода датчика 4 напряжения на один из входов (1) преобразователя 10 и текущего значения тока I₁ двигателя, поступающего с выхода датчика 5 тока на второй вход функционального преобразователя 10 путем векторного сложения сигнала датчика 4 напряжения с сигналом датчика 5 тока, соответствующего падению напряжения на активном сопротивлении обмотки статора.Obviously, in controller 8 with first-order astatism, Δe ₁ in steady-state modes of operation of the electric drive is a high order of smallness compared to

and e ₁ , and therefore the relation

. However, in the dynamic modes of the electric drive, Δe ₁ cannot be neglected. The current value of the EMF (e ₁ ) is determined by the functional converter 10 from the current value of the voltage U _{1 of the} motor coming from the output of the voltage sensor 4 to one of the inputs (1) of the converter 10 and the current value of current I _{1 of the} motor coming from the output of the current sensor 5 to the second the input of the functional Converter 10 by vector addition of the signal of the voltage sensor 4 with the signal of the current sensor 5, corresponding to the voltage drop across the active resistance of the stator winding.

, поступающего с его выхода на первый вход регулятора 9 частоты поля статора двигателя, и из сигнала Δe₁ с выхода датчика 11 ошибки ЭДС двигателя, поступающего на второй вход регулятора 9 частоты реализует функцию управления видаThe regulator 9 of the frequency of the field of the stator of the engine from the signal setter 12

coming from its output to the first input of the frequency controller 9 of the stator field of the motor, and from the signal Δe ₁ from the output of the sensor 11 of the error of the EMF of the engine, coming to the second input of the frequency controller 9, implements a control function of the form

- функция управления, реализуемая датчиком 11 ошибки ЭДС двигателя… (3).Where

- a control function implemented by the sensor 11 errors of the EMF of the engine ... (3).

Given the expression (3) we obtain:

where U _α is the frequency control signal of the stator field, coming from the output of the frequency controller 9 to the first input of the inverter control unit 7.

Thus, the control signal U _{α by the} frequency of the stator field determines such a frequency α of the stator field that at any time corresponds to the current value of the motor EMF.

If when accelerating the engine 6, its speed lags behind the rate of increase of the output signal of the intensity adjuster 12, which determines the frequency of the stator field of the engine, the slip and the motor current begin to increase, and when current limiting comes into operation, the motor EMF e ₁ and the feedback signal for EMF a therefore, the frequency of the stator field and the speed of the motor, up to a complete stop ("tipping" of the motor).

To prevent this, the quantization unit continuously quantizes the feedback signal from the motor EMF from the output of the functional converter 10 to the input of the quantization unit 13, time-quantized pulses continuously output from the output of the quantization unit to the input of the decisive unit, in which the current the amplitudes of the quantized pulses and the sign of the current increment of the amplitudes of the quantized pulses is continuously determined by calculating the second differences of the instantaneous amplitudes for azhdyh three consecutive quantized pulses according to the equation:

where X _n is the nth quantized momentum,

X _{n + 1} - (n + 1) -th quantized momentum,

X _{n + 2} - (n + 2) -th quantized momentum, where

n = 1, 2 ... ~.

Signal Sign Δ ² X _n from the output of the decision block is input to the correction block 15, which either stops the intensity adjuster and accelerates the engine at Δ ² X _n <0, i.e. if Sign is negative, until Δ ² X _n ≥0, i.e. Sign is positive. In this case, the output signal of the setpoint will continue to increase, and the engine will continue to accelerate.

If during acceleration of the engine Δ ² X _n ≥0, i.e. Sign is positive, then the intensity control does not stop, and the acceleration of the engine continues.

If during engine braking Δ ² Xn≤0, i.e. Sign is negative, then the engine braking continues without overvoltage on the power elements of the inverter, i.e. when the magnitude of the negative slip of the engine does not increase.

If during engine braking Δ ² X _n > 0, i.e. Sign is positive, then the intensity adjuster stops, and engine braking continues by coasting until Δ ² X _n ≤0, i.e. Sign is negative and the intensity adjuster will continue to change the output signal towards a further decrease, i.e. the engine will continue active braking.

A device for controlling a digital frequency-controlled electric drive will not only improve the dynamics of the electric drive without “tipping over” the engine during acceleration and without overvoltage on the power elements of the converter when it brakes, but significantly reduce the dimensions of the device and increase the flexibility of controlling the electric drive in terms of changing its operation algorithms and technical specifications through appropriate microcontroller control software.

According to the invention, a prototype of an electric drive with a power of 500 W and an output frequency of 50 Hz for a transfer water pump was developed and tested.

Claims (1)

A device for controlling a digital variable frequency drive containing a constant voltage source and an inverter connected to each other via an LC filter, a voltage sensor connected to the stator of an induction motor, an intensity adjuster, a functional converter and an inverter control unit connected to the inverter, while two the inverter control unit inputs are connected, respectively, to the stator field frequency regulator and the motor EMF regulator, the output of the intensity adjuster is connected to the regulator EMF-directly, and to the frequency controller of the stator field through one of the inputs of the motor EMF error sensor, the other input of which is connected to the second input of the motor EMF controller and simultaneously with the output of the functional converter, in which one of the inputs is connected to a voltage sensor, different the fact that the device includes elements for optimizing the speed of acceleration and deceleration of the motor: a current sensor, a quantization unit, a decision unit and a correction unit, while the current sensor is connected in series between the inverter and the sensor voltage, and its output is connected to the second input of the functional converter, while the output of the functional converter is additionally connected to a quantization unit, which is connected in series with a decoding device and a correction unit, and the output of the latter is connected to the input of the intensity adjuster.