DE2756918A1 - PROCEDURE FOR CONTROLLING AND REGULATING THE SPEED OF A INVERTER-SUPPLIED ASYNCHRONOUS MACHINE - Google Patents

Description

PPOWN. BOVERI & CIE · AKTIENGESELLSCHAFT [CJ ; ~ ^:) VV

MANNHEI M BROW. '> FBOVt R ι

Np.-ITr. 4 ^ 9/77 Mannheim, December 12, 1977

ZFE / P3-Kr / Bt

Method for controlling and regulating the speed of a converter- fed asynchronous machine.

The invention relates to a method for controlling and regulating the speed of an asynchronous machine, which consists of is fed to a converter with stamped Stnm where the control is carried out by a subordinate current control, in which one of the value of the slip frequency f corresponding electrical variable and a frequency f corresponding to the actual value of a rotor speed proportional electrical variable the control variable for the frequency f .. of the current output by the converter is formed will.

A regulation for converter-fed asynchronous machines with an impressed stator current is known from the Siemens magazine Paragraph 42 (1968), Issue 9, page 773 ff. In this control device, there is a subordinate current control with which the current in the asynchronous machine is regulated to a setpoint specified by the higher-level control. The actual current value for this control loop is recorded either in the DC link or in the supply lines to the line -commutated converter at the input.

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A similarly known regulating device "for control
and control of the speed of an asynchronous motor is shown in FIG. 1. This control device has a rectifier 1 for the intermediate circuit current from an alternating current network. The DC link 2 contains a choke; coil 5, via which the rectifier is connected to an inverter 4. at its AC side! Connections the .'synchronous machine 5 is connected. ! A transmitter S is connected to it, in which the frequency z " corresponding to the engine rotation beam is determined. These
Frequency f is fed to a summation point 7 together with a frequency i & proportional to the load. This one
a speed controller S is connected downstream. Its output signal
becomes a second sum point 9 together with the frequency f_
supplied, whose output frequency f. as a control variable for
the change frequency of the Λ synchronous machine via a
Rate ¹ O is supplied to the V, ^R A echseirichter. That
The output signal f _{0 of} the speed controller 8 and the frequency f are fed to a characteristic curve 11 in which the behavior of the asynchronous machine 5 is simulated. That
Output signal of the characteristic curve. ^] Iedes 11 w: rd used as current Sullv / ert I _so in. This current setpoint value I ₃₀ -II becomes

a sum point 12 is supplied. As actual current value
the sum point 12 receives either the actual current value determined in the intermediate circuit or that in the supply lines
actual current value recorded by the rectifier. The sum point 12
is connected to a current regulator 13. The output signal ! this current regulator is fed to the rectifier 1 via a control unit 14. '

From ETZ-A 1975, page 520 ff. Is a circuit for 'feeding an asynchronous machine with a line -commutated
Rectifier, an intermediate circuit and a self-

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led inverter known. In the circuit arrangement described there, the asynchronous machine from the Inverter fed rectangular power blocks. These rectangular flow blocks contain next to the desired Fundamental oscillation of the current still contains a large number of harmonics of high frequencies that lead to pendulum moments in the Asynchronous machine lead. Capacitors are provided to commutate the current in this inverter. the The size of the voltage across these capacitors depends on the one hand on the motor voltage and its phase angle compared to the motor current, on the other hand from the motor current, the machine leakage inductances and the capacitor size. The capacitor size is again dependent on the machine leakage inductances the maximum scatter frequency and in particular the ratio of motor voltage to motor current im Idle operation.

In this known method for controlling an asynchronous motor fed by a converter, the at Calculation of the nominal flux on which the motor is based, regardless of the load and supply frequency, as constant as possible held. The torque is set by specifying the slip frequency. The motor current is dependent on specified by the slip frequency of the machine in such a way that the flux of the motor remains constant. i.e. in the area in which the maximum voltage is reached and the motor voltage when the stator frequency increases can no longer be increased, the maximum voltage and the torque are kept constant of the motor can only be set by changing the slip frequency.

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In the known method, therefore, to control the!

Asynchronous motor from idling to full load operation at:

constant flux the slip frequency of the motor between,

Slip frequency zero and the required maximum! Adjusted slip frequency. The point of interpretation for size of the commutation capacitor results from one of the

like control method at maximum feed frequency. In no-load operation, the slip frequency is zero and the motor current corresponds to the magnetizing current. The maximum motor voltage to ratio results at this operating point Motor current which, together with the maximum frequency, determines the size of the commutation capacitor. ' In full load operation with a correspondingly high current, however, there is an increase across this capacitor compared to idle operation much larger capacitor voltage. The semiconductor element ^ in the inverter must also designed for this high capacitor voltage. In addition, the machine insulation and the ripple of the Intermediate circuit current, which determines the size and weight of the intermediate circuit inductor, influences.

This type of current control is sufficient for a large operating range of the drive system. In the event of malfunctions in the self-commutated converter, the current in the intermediate circuit can be limited relatively easily. _;

In the case of converters with impressed current, operating at higher frequencies and lower currents can: states occur in which part of the current flowing in the intermediate circuit flows past the asynchronous machine. A regulated operation of the asynchronous machine is then not possible with the type of current regulation mentioned above more is possible.

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When dimensioning this area of "multiple commutations in the self-commutated converter" avoided. Due to this, however, voltage stresses occur when the machine is operated with high machine currents Valves of the self-commutated converter, which greatly reduce the use of the drive system at higher frequencies restrict.

There are known measures for reducing excessively high voltages on or on the Konnutierungskondensatoren that a feedback Provide excess energy via an inverter in the feeding network and thus very costly (DT-AS 25 15 223, DT-AS 24 55 765).

The invention is based on the object of specifying a method that is used when operating at higher frequencies and smaller currents also ensure that the asynchronous machine is dynamically controlled. The procedure should also be created so that in the range of higher frequencies when operating with large machine currents high voltage stresses on the valves of the self-commutated converter are prevented.

The solution to the problem posed is, according to the invention, that the current actual value for the current control in the Leads to the asynchronous machine is detected, and that in the DC link or in the leads of the line-commutated converter, only the actual current value for limiting the intermediate circuit current is determined.

The frequency limit of multiple commutations is reached with the inverter when in a commutation group T 11, T12, T13, D1, D2, D3 or D4, D5, D6, T14, T15, T16 the beginning of the following commutation with the

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The end of the last coincides, ie a thyristor ignition is already initiated in the same commutation group, although diode commutation is still taking place. This fact has the effect that the processes in the two commutation groups influence each other. The inverter now makes unused Itrom paths available: The two capacitor groups C1, C ?, C3 or C4, C5, C6 are mutually recharged, causing current to bypass the machine. This causes a reduction in the current-time area in the machine phases with the intermediate circuit current remaining constant.

The measured value recorded in the supply lines to the asynchronous machine for the subordinate current control is correct in the "normal" Operating range with the value measured in the intermediate circle match. He becomes the subordinate current control that is now represents a real motor current control, as current actual value fed. With the specified procedure, it is possible with the same effort in the power section to set the frequency range, in which the drive system can be operated.

The circuit for carrying out the method is characterized in that the current setpoint value is a sum point and the actual motor current value is managed in such a way that the summation point is connected to a current controller whose output signal is fed to the rectifier via a limiter, and that the limiter is the actual value of the current of the intermediate circuit or the feed lines of the rectifier.

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The usual way is between the self-guided inverter and the third summation point as well as between the line-commutated rectifier and the limiter Tax rate arranged.

[The invention is explained in more detail below with reference to drawings. Show it:

1 shows an already known circuit for regulating the speed of an asynchronous machine,

! Fig. 2 shows a circuit for performing the fiction ^! according to the procedure.

■ The circuit shown in Figure 2 for performing the method comprises a rectifier 1, a DC intermediate circuit 2 with 3iner reactor 3 and an inverter. 4 The AC connections R1, S1 and T1

'of the rectifier 1 are connected to an alternating current network. The rectifier is a three-phase bridge circuit with three bridge arms each with two series-connected thyristors T1 and T4; T2 and T5; T3 and T6 trained. The rectifier is connected to the inverter 4 via the choke coil 3. This is also designed as a three-phase bridge circuit and has three bridge arms, each with two series-connected thyristors T11 and TH; T12 and T15; T13 and T16. Each of the two bridge halves of the inverter 4 is equipped with a commutation device made up of commutation capacitors C1, C2 and C3 and / or. C4, C5 and C6 and diodes D1, D2 and D3 or D4, D5 and D6 are provided for phase sequence deletion. A diode D1, D2 ... D6 is connected to each thyristor T11, T12 ... T16. Between

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the connecting lines of the thyristors T11, T12, T13 or T14, T15, T16 and the diodes D1, D2, D3 or D4, D5, D6 are the commutation capacitors C1, C2, C3 and C4, C5 and C6 arranged. The circuit of this commutation device is already known from ETZ-A Vol. 96 (1975) H. 11, page 520 et seq.

; The inverter 4 is fed with an impressed direct current Id. To its AC connections R2,

An asynchronous machine 5 is connected to S2 and T2. ; This is connected to a transmitter 6, which is one of the 'Motor speed corresponding frequency f generated. These Frequency f is combined with one of the load condition

I *

corresponding frequency f * a first summation point 7 fed.

This frequency f * can, for example, in a frequency ! generator 21 are generated. The sum point 7 is connected to a speed controller 8, to which the sum value

the frequency f * and the Frequena f is supplied. The output signal of this speed controller 8 corresponds to the slip frequency fo and is fed as the actual setpoint frequency together with the frequency f to a second summation point 9. The sum value of the frequency fp and the frequency fv / ird is fed to the inverter 4 via a control set 10 as a control variable f... For the stator frequency of the asynchronous machine 5. The output signal fg of the speed controller 8 and the control variable f ^ for the stator frequency are fed to a characteristic element 11. The behavior of the asynchronous machine 5 is simulated in this. The characteristic element Π is connected to a third summation point 12. The output signal of the characteristic element 11 is fed to the sum point 12 as a current setpoint Ι __-, _Ί . In the supply lines R2, S2 and T2

* in particular the deviation between ··· / ···

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of the asynchronous motor 5, measuring points 36 for determining the motor current are installed. The current values determined in the measuring points 36 are the summation point 12 is supplied as a motor current value ¹ Mist ^{for urvterla} e ^{he "te} current Rege lung. The summing junction 12 is a flow regulator 13 downstream of the sum value to the current command value I _goll and the motor current j ^ gt ^a ls input signal receives actual value?. the output of the current controller 13 outputs the modulation of the rectifier 1 for the Zv / ischenkreisstroro before. to limit the intermediate circuit current, the output of the current controller 13 is supplied to a limiter 14th a measurement point 37 for determining the current actual value Tß4 _S ^ - i ^s "t arranged in the intermediate circuit in front of the choke coil 3 or in the alternating current supply lines R1, S1, T1. _{The actual current value I ßist} determined in the measuring point 37 is only used to limit the intermediate circuit current and is supplied to the limiter 14 for this purpose. The output signal of the limiter 14 is fed to the rectifier 1 via a control unit 15.

especially the difference between

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Claims (1)

Claims A method for controlling and regulating the speed of an asynchronous machine which is fed from an inverter with impressed current, wherein, the regulation by a subordinate current regulation, in which from one to V / ^r ert the slip frequency (f _o) the corresponding electrical quantity and a the actual value of an electrical variable proportional to the rotor speed (E " _n ) corresponding to the control variable for the frequency (T ₁ ) of the current output by the converter, characterized in that the actual current value for the current control is detected in the supply lines to the asynchronous machine, and that in the intermediate circuit or in the supply lines of the self-commutated converter only the actual current value for limiting the intermediate circuit current is determined. 2.Circuit for carrying out the method with a rectifier fed by an alternating current source, whose direct current output is connected via a choke coil to a self-commutating inverter, to whose alternating current side an asynchronous machine is connected, with an encoder for determining a frequency of the motor speed corresponding to _n ), a speed controller, to which the deviation between one of the load 0Θ9827 / ΟΟ24 κ η 12/12/1977 659/77 state corresponding frequency (f #) and the frequency (f) zurre f'Jhrt v. ^r i ^ d, e iners I'Iennlirienrjlisd which the slip frequency _(f?) corresponding output signal of the speed controller and the difference zv / delete this frequency _f? ) wnd the motor speed proportional frequency (f ^) formed control variable (f (11) as Jvtro ~ ekennzeic ^v : ne '.' seen in τ.,;.: or the ^Ύ . '"" · τ.ντ- or werdtvi,: - nachgeschalt'j ": via a rf J.es Gieic · -;:. ■ -' ^ •• ■ "'Grenzer,'! ■ '". · ^ - s Stror. ·' ■!: -, .. ■ ti den ZuJ ■ - ■.:.:.; ■ : ■: -sits. ) is used, thereby prefixing SunmenpunJ-rt (12) ( (Tr ..; .. · "+.) Is supplied WlSX : 3ct (12) a current regulator (13) output of the current regulator (1?) Is the control rate (15) 'en, and that the ri current actual value (Ir ,. ₊ ). ^- nd / odor of the current values Ο of the rectifier (1) 609827/0024