DE3224301A1 - Circuit arrangement for operating a three-phase machine, which is supplied from a DC-link converter, in the field-weakening range - Google Patents

Abstract

If a three-phase machine (5) is braked in the field-weakening mode, an undesirable increase in the DC-link circuit voltage occurs in the case of a converter which supplies the three-phase machine (5) with a variable DC-link circuit voltage and frequency tracking. In order to avoid this, an additional desired-value transmitter (15) is provided which, from the DC-link circuit voltage control variable, supplies a continuously increasing desired value as an additional value to the fundamental value for frequency tracking when the DC-link circuit voltage exceeds 90% of the maximum permissible value. The additional desired value-transmitter (15) is at the same time connected to the voltage regulator (8) via which the DC-link circuit voltage is regulated. <IMAGE>

Description

- 3 - B 82/33 Ham

Circuit arrangement for operating one of a DC link converter powered three-phase machine in the field weakening range

description

The invention relates to a circuit arrangement according to the preamble of claim 1. Such a circuit arrangement Circuit arrangement is known from DE-OS 30 21 119.

Both known arrangements give when operating in the field weakening range the additional setpoint generator emits an additional signal that increases with the setpoint, through which despite Maintaining the nominal voltage at a higher frequency Machine converter is generated. Should the three-phase machine are braked, the reference variable set on the setpoint generator is reduced. But that increases the intermediate circuit voltage because of the corresponding Frequency reduction, the machine works as a generator and feeds into the intermediate circuit. To avoid such Overvoltages in the intermediate circuit, a discriminator is provided in the known arrangement, which then generates an error signal to increase the frequency emits until the intermediate circuit voltage again corresponds to the maximum permissible value. After that, further braking causes an increase in voltage in the intermediate circuit, which is caused by a renewed error signal to increase the frequency is eliminated by the discriminator. The discriminator works in the sense of a two-point control; the frequency always oscillates back and forth when braking, which results in unsteady braking behavior of the. J3 three-phase machine entails.

The invention is based on the object of a circuit arrangement to avoid the discontinuous braking when operating in the field weakened area of the type specified at the beginning.

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This object is achieved according to the invention by the claims 1 marked features solved.

The additional target size is thus already below the Rated frequency of the three-phase machine activated, so that when When braking, no overvoltage can occur in the intermediate circuit can. Rather, the addition of the additional variable to the frequency tracking of the machine converter automatically for a required frequency increase below the maximum permissible value of the intermediate circuit voltage taken care of.

Advantageous refinements of the invention are set out in the subclaims marked.

The invention will be explained below with reference to an embodiment shown in the drawing will. Show it

Fig. 1. a principle circuit diagram of the circuit arrangement according to the invention and

2 shows the course of the intermediate circuit voltage

depending on the frequency of the machine converter or depending

speed from the setpoint of the machine speed.

Fig. 1 shows an intermediate circuit converter, which consists of a controlled line converter 1, an intermediate circuit with an intermediate circuit capacitor 3 and a smoothing reactor 4 and a machine converter 2 is formed. The machine converter 2 feeds a three-phase motor 5

The converter works with a variable intermediate circuit voltage, which is provided by the line converter 1. A setpoint generator 7, on which the desired machine speed n _g - ^ can be set, is used to set the variable intermediate circuit voltage. The actual value xg of the intermediate circuit voltage

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v: is determined via a voltage sensing element 6 and compared with the specified reference variable n _s -, -. The control deviation serves as the input variable of a voltage regulator S, the output variable of which is used as a current control variable for a 3tror.regier 9 connected downstream of it. This current control variable is compared with the actual current value Xj · ^ recorded via a current transformer 11. Corresponding to the control deviation of the current, the current regulator 9 with its output signal influences the rapid control set 10 for the valves of the controlled mains converter 1, so that these are ignited according to the desired intermediate circuit voltage U 1.

In the usual way, the frequency of the machine converter 2 is adjusted in accordance with the applied intermediate circuit voltage. For this purpose, the actual value x _{TT is} the over

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the voltage detection element 6 applied the detected intermediate circuit voltage to the input of an adaptation controller 12, which is followed by a voltage-frequency converter 13. The output frequency of the voltage-frequency converter 13 influences t> e a control set 14, with which the valves of the machine converter 2 f ^ equence-appropriate for the motor 5 . be switched.

According to the invention, an additional target value transmitter 15 is provided for operating the three-phase motor 5 in the field weakening range, which becomes active when 90% of the maximum permissible value of the intermediate circuit voltage is exceeded. This then outputs an additional variable that increases continuously up to the maximum permissible value of the intermediate circuit voltage, which is input to the adaptation controller 12 as an additional reference variable to the value Χττ- added. This increases the frequency of the machine current

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judge 2 between (ο, 9 ··· 1) χ U, ^ dm "- ^{= maximum} intermediate ^{circuit" 1} "svoltage) disproportionately, without an overvoltage normally occurring during braking. Braking takes place continuously and without frequency fluctuations.

At the same time, the additional variable provided by the additional setpoint generator is also specified for the voltage regulator 8, about a linear relationship between the speed reference variable and the frequency to get. This makes the frequency dependent exclusively on the Actual voltage value preserved.

By inserting the additional variable from the additional setpoint generator 15, the usual overvoltage limitation can no longer take place via the speed setpoint specification. Instead, a maximum value limiter for the intermediate circuit voltage, which is connected to the voltage regulator 8, is provided in a further embodiment of the invention. The maximum value limiter 16 is activated when the actual value x _{TT of} the intermediate circuit voltage

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a specified maximum value ^ YjA _may - exceeds. The overvoltage limitation is therefore independent of the additional variable because it compares the actual controlled variable (x _TT ) with the

Compares the maximum value and corrects the voltage regulator 8.

Fig. 2 shows the course of the intermediate circuit voltage U, depending on the frequency f of the machine converter or depending on the value set on the setpoint generator 7 Speed setpoint n ^ ■, ·, for the three-phase motor 5. As can be seen, the intermediate circuit voltage U increases with the frequency

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quenz f or the speed _{setpoint Ho 0} -.-, linearly, so that in the usual way at the highest permissible value of the intermediate circuit voltage U, and the nominal frequency of the machine f

-yf

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the field weakening range begins. Instead, however by activating the additional setpoint generator 15 at 0.9 · υ. a disproportionate increase in frequency in the Field weakening range reached until the maximum permissible DC link voltage is reached «

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Claims (3)

Licentia Patent-Verwaltungs-GmbH
Theodor-Stern-Kai 1 Frankfurt 70 Ham / Te B 82/33 Ham Circuit arrangement for operating one of a DC link converter powered three-phase machine in the field weakening range Claims (1.) Circuit arrangement for operating a three-phase machine in the field weakening range with a DC link converter feeding the three-phase machine, - Which has a converter providing a variable intermediate circuit voltage on the input side, which can be ignited as a function of the control deviation of a voltage regulator, the control deviation being through Comparison of the reference variable proportional to the motor speed with the controlled variable proportional to the DC link voltage is formed - which has a machine converter on the output side, which is dependent on an adaptation controller is tracked by the intermediate circuit voltage and _ 2 - JZZ4JU I 2 - B 82/33 Ham - in which an additional setpoint generator is provided for operation in the field weakening range, characterized, that the additional setpoint generator (I5) is connected to the input of the adaptation controller (12) is connected and above an actual value of the intermediate circuit voltage of more than 90% of the maximum permissible value one to the maximum permissible value provides continuously increasing additional variable. 2. Circuit arrangement according to claim 1, characterized in that that the additional setpoint generator (15) provides an additional linear variable. 3. Circuit arrangement according to one of claims 1 or 2, characterized in that that the additional setpoint generator (15) is also connected to the voltage regulator (8). 4-. Circuit arrangement according to one of Claims 1 to 3 » characterized, that a maximum value limiter (16) for the intermediate circuit voltage that is not influenced by the additional setpoint generator (15) is connected to the voltage regulator (8).