SU922983A1 - Device for control of frequency-adjustable electric drive - Google Patents

Description

The invention relates to electrical engineering and can be used in automated AC drives with frequency converters.

A device for controlling the frequency ^5-regulated electric drive comprising ramp-function generator, a semiconductor amplifier, feedback sensors on the engine speed and vice conjugate motor connected via diodes to the reference input of the semiconductor amplifier. A feedback element is included in the feedback circuit. In this device, the rate of increase of the output signal of the intensity adjuster is determined by the rate of rise of the signal from the motor voltage sensor or speed sensor. When braking the engine, the speed of frequency reduction is regulated by the output signal of the voltage or speed sensor when they are connected to the input of the intensity control after the breakdown of the threshold element ϋ].

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The disadvantages of this device are the ability of the drive self-condition mode when it is braked and the impossibility of using this device to generate speed-optimized starting and brake modes of the drive with two-zone control when the stator field frequency of the engine is higher than the nominal value and the voltage is equal to the nominal value.

The closest technical solution to the invention is a device for controlling a variable frequency drive, containing a frequency converter with a pronounced DC link, consisting of a series-connected adjustable rectifier, filter and autonomous current inverter, rectifier and inverter control units connected respectively to the rectifier and inverter , current and voltage sensors, ask3 922983

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A common frequency generator, the output of which is connected to the control unit of the inverter and the first input to the output of the setpoint in-. intensity, the second input of the master oscillator frequency - to the output correction unit ₅ tion frequency having an input connected to the output mismatch meter, the first misalignment meter input connected to the output of the voltage sensor, and between the intensity setting unit, and on, the rectifier control unit connected to the conversion unit of the master

 signal into the voltage regulation signal, the output of the specified conversion unit is additionally connected to, 5, the second input of the error meter G2].

A disadvantage of the known device is the difficulty of matching the optimal starting and braking modes _{20 of the} electric drive, since the error meter signal affects only the frequency control channel.

The purpose of the invention is to simplify the coordination of acceleration and deceleration modes. ₂₅ This goal is achieved by the fact that

a device for controlling the variable frequency electric drive comprising a frequency converter pronounced DC link, co- ₃₀ standing from the series-connected controlled rectifier, a filter and an inverter, the output of which connects to the induction motor, control units rectifier and inverter, respectively connected to the rectifier and an inverter that drives a frequency generator, the output of which is connected to the inverter control unit, voltage and current sensors of the engine, a comparator, motor EMF extraction unit and EMF job restriction unit, the output of which is connected to the rectifier control unit and to one input of the comparison terminal, the other input of which is connected to the voltage and current sensors through the EMF extraction unit, intensity setter, whose output is connected to the inputs of the master frequency generator and setting limit block EMF introduced key epe- semiconductor ment ⁵⁰ and a comparator, wherein the comparator

. It is included at the entrance ramp-function generator, the key element is coupled to the input and output of the comparator, a control electrode of the key element ⁵⁵ nen accession to the output of the comparator unit.

ι The drawing shows a schematic block diagram of a device for controlling a variable frequency drive.

The device contains a frequency converter, consisting of a series-connected adjustable rectifier 1, a smoothing filter 2, and an inverter

3. The rectifier 1 is connected to the rectifier control unit 4, and the inverter 3 is connected, via the inverter control unit 5, to the master frequency generator 6. The sensors 7 voltage, 8 current connected outputs with the inputs of the block 9 of the allocation of the EMF, the output of which is connected to the unit 10 of the comparison. The intensity setting device 11 comprises a comparator 12 shunted by the key element 13, the control electrode of which is connected to the comparison unit 10. Unit 14 limiting the EMF outputs is connected to unit 4 and to the input of unit 10. comparison. The output of the frequency converter is connected to the engine 15.

The device works as follows. ^one

If, during engine acceleration, the difference between the set and true values of the EMF exceeds the setting value selected in accordance with the allowable value of the slip pulsations, the key element * ¹ 13 of the comparator is triggered

12, the intensity setting unit, as a result of which the change in the output signal of the latter stops, and, consequently, the change in the EMF reference and the frequency of the motor field. When the difference between the set and true values of the EMF of the engine becomes less than the setpoint value, the additional key element 13 closes, as a result of which the output signal of the intensity setter and the reference signals of the EMF and frequency of the motor field will continue to change, causing the engine to accelerate further.

When braking the drive, when the difference between the true and specified values of the EMF exceeds the setpoint value selected in accordance with the allowable value of slip pulsations, the allowable amount of overvoltages on the converter elements determined in the specified mode, the additional key element is triggered

13, which shunts the comparator 12 of the intensity control unit, as a result of which the change in the EMF reference and the frequency of the motor field stops.

When the difference between the true and the set EMF values becomes less than the set value, the additional switch5 922983 6

Element 13 closes, causing the WZS and field frequency reference signals to continue changing, causing further engine deceleration. This eliminates the 'self-excitation' mode 5

electric drive.

The proposed device allows to improve the quality of electric drive regulation by forming optimal speeds of acceleration and deceleration, which expands its functional capabilities and scope,

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Claims (1)

Claim A device for controlling a variable frequency drive, containing a frequency converter with a clearly defined 20 dc link, consisting of a series-connected adjustable rectifier, filter and inverter, the output of which is used to connect to an asynchronous motor — 25, the rectifier and inverter control units connected respectively to the rectifier and the inverter, the master frequency generator, the output of which is connected to the inverter control unit, voltage and current sensors of the engine, the comparison unit , a motor EMF extraction unit and a EMF job restriction unit> whose output is connected to a rectifier control unit and to one input of a comparator unit, the other input of which is connected to voltage and current sensors, an intensity setpoint generator, an output connected to inputs of a master oscillator through the allocation unit EMF and block limiting the EMF, characterized in that, e circuit to simplify the coordination of acceleration and deceleration of the drive, additionally introduced semiconductor key element and comparator, with the comparator on chen inlet ramp-function generator, a key element connected to the input and output of the comparator, a control electrode of the key element is coupled to the output of the comparator unit. .