DE2344330A1 - Control circuit for three-phase static converter - has loop gain varied according to current-gap-modes current - Google Patents

Abstract

The control circuit, for a 3-phase static converter, has a current regulator, a control unit and a device to alter at least one of the regulating control circuit parameters depending on the gap or break current. The circuit loop gain is altered continuously depending on a reference value. The reference value may be the actual value of the instantaneous current or its mean. The reference value is limited to an upper level which corresponds to the current at the boundary of the gap-mode of operation so that the loop gain is only affected below this boundary.

Description

Control device for a controlled converter arrangement

The invention relates to a control device for a controlled converter arrangement with a current regulator, a control rate and a device for the leakage current-dependent adaptation of at least one control loop parameter.

In a "known such control device for the Current control of converters in the discontinuous and non-discontinuous area is a controller with switchable time behavior and a changeover device is provided (DT-AS 1 957 599) · The changeover is carried out in such a way that the controller is in the non-discontinuous range and while the current is being carried In the gaping area a PI behavior, on the other hand an I behavior in the current gaps of the gaping area having.

The constant switching of the time response of the current regulator can be considerable with this known regulating device Bring unrest into the control loop. In addition, with the known control device only for the special case that a PI controller with an integral time corresponding to the time constants of the consumer circuit is used, equally good dynamic control conditions both in the non-discontinuous and in the discontinuous area achieve.

The invention is therefore based on the object of using simple means to provide a leakage current-adapted current control for To create power converters that are independent of the type

509830/0360

VPA 73/3228 - 2 of the current controller and its parameter setting.

According to the invention, this is a member for influencing the Loop gain in constant dependence on a current value or suggested by a variable derived from a current value.

It was found that the deterioration in control characteristics of the current control loop of a converter in the gap area mainly due to the change in gain is. The invention therefore proposes influencing the loop gain. The influencing takes place however, not in a discontinuous switching operation, but rather a constant influencing is carried out. From the Finding out that the influence of the control angle of the converter is of minor importance, acts as the variable influencing the loop gain is a Stram value or a quantity derived from it. By inserting a link to influence the loop gain the current controller can be left unchanged. This means that they remain independent of the type of controller used and the applied optimization rule the control dynamic conditions in the gap and non-gap area the same Well.

The current value or the variable derived from it is limited to an upper value that corresponds to the current at the gap limit corresponds, the element being adjusted in such a way that the loop gain is only influenced below the upper limit value. Influencing the gain this only takes place in the discontinuous area of the current.

509830/0360

VPA 73/3228

The current value or the variable derived therefrom is expediently also set to a lower limit value limit the same polarity, so that even with very small currents in the gap area, a defined influence on the Loop gain takes place without the zero point error of the components used are disturbing.

The easiest way to influence the loop gain is to make it dependent on the Bring instantaneous value of the current actual value. The loop gain can, however, also be a constant function of the Current mean value are brought because the change in the system gain in the gap area is a good approximation Puncture the current mean value is. However, it is also possible to use the peak value of the current, since im Void area the mean is a puncture of the peak value and the control angle.

According to one embodiment of the invention, the output signal can be derived from a current value The substitute timer is used, which simulates the transition behavior of the control loop and is acted upon by the current setpoint will. It is particularly advantageous if the member has a puncture transmitter for influencing the loop gain with a puncture corresponding to the course of the loop gain depending on the current in the gap area is.

To influence the loop gain, a divider in the input or output of the current controller or a Multipliers can be provided in the feedback of the current control amplifier or the control differential amplifier. If it requires a special application, according to the invention, not only can the loop gain in continuous

-A- 509830 / 0-3 60

YPA 73/3228

dependence on a current value or a quantity derived from it, but it can also do that Time behavior of the current controller can be appropriately influenced. Also influencing the time behavior of the current regulator takes place according to the invention not in discontinuous switching operation, but in constant dependence on a current value or a quantity derived from this.

Embodiments of the invention and their in the subclaims Embodiments marked are described in more detail below with reference to the figures.

Fig. 1 shows the use of a current-regulated converter for speed control of a direct current motor 1, which has a converter 2 as an actuator from a Three-phase network RST is fed. The tachometer generator 3 maps the speed η of the DC motor 1. The control difference from the actual value of the speed η and its setpoint n * controls the speed controller 4, whose output variable I * forms the setpoint for the subordinate current controller 5. A current transformer 6 supplies a at its output terminal 7 The G-I calibration voltage representing the converter current and thus also the motor current, which is subtractive to the comparison point 10 is supplied. The control difference from the actual value I of the current and the associated setpoint I * controls the current regulator 5, the output of which is connected to the input terminal 8 a tax rate 9 is connected to the required Outputs ignition pulses to the controlled semiconductor valves of the converter 2.

Fig. 2 shows the two typical operating states for the time course of the current I of the converter in the gap area A and in the non-intermittent area B. In the intermittent area A, times of current conduction S alternate with currentless pauses P

- 5 509830/0360

VPA 73/3228

from: the current "cuts out". This loophole occurs depending on the time constant of the consumer group below one certain current value. The intermittent operation and its effects on the control behavior are described in detail in Möltgen "Line-commutated converters with Thyristors ", 2nd edition, 1970, pages 46 to 52 and 116 118. It is essential to reduce the armature circuit gain as the duration of the currentless period increases Breaks. A for the non-intermittent area B according to certain criteria, e.g. symmetrical optimum or amount optimum, The set controller therefore finds a controlled system with reduced gain in the gap area and can therefore not with intermittent operation in terms of dynamic control do more of the same as in non-discontinuous operation.

To remedy this, the invention proposes a link for influencing the loop gain in constant dependence on one Current value or a quantity derived therefrom. In the embodiment of the Pig. 1 is as a member of the Divider 11 is provided in the signal input of the current regulator 5. The divider 11 is the system deviation as the dividend and a current mean value entered as a divisor, that of a smoothing element acted upon by the current actual value I. 12 is formed, the time constant of which is dimensioned according to the number of pulses of the converter used. The output of the smoothing element 12 is limited by the limiting stage 13 to a value that corresponds to the current value at the Corresponds to the gap limit. The divider 11 is balanced in such a way that its output signal with that supplied as a dividend Deviation corresponds if the limiting value is present at the divisor input. This corresponds to other places of division by 1. The district gain is therefore only influenced below the gap limit in the gap area A.

- 6 509830/0360

VPA 73/3228

-S-

In the embodiment of FIG. 3, that is at the output terminal 7 of the current transformer 6 pending current actual value I. guided via the smoothing member 14 to the puncture transmitter 15, which is a function of the course of the loop gain has a corresponding function of the current in the gap area. The output signal of the function generator 15 represents a is derived from the current value and is entered as a factor in the multiplier 16, which is in the feedback of the control amplifier 17 of the current regulator 18 is located.

The function generator 15 can, for example, be an operational amplifier be realized, in whose input and / or negative feedback circuits biased threshold value diodes are arranged, which are successively permeable depending on the input voltage and so the Change the gain of the operational amplifier as desired. The output signal of the Function generator 15 is limited to the current value at the gap limit. In this example, the current is measured on the rotary ytrical side takes place, the function generator 15 only needs to be controllable in the 1st quadrant, in.

In the embodiment of FIG. 4, a divider 19 is provided in the output of the current regulator 5, which is used as a dividend the output voltage of the current regulator 5 and, as a divisor, an average current value L, which is entered by a member 20 is formed from the actual current value and is limited to a value that corresponds to the current at the gap limit.

FIG. 5 shows an averaging device 20a suitable for this purpose for the control angle for the ignition pulses of the converter considered. The averaging unit contains two integration amplifiers 21, 22 to which the actual current value I is applied; their feedback capacitors 23, 24 alternately from

- 7 - 509830/0360

VPA 73/3228

Field effect transistors 25, 26 can be bridged as electronic switches. The control electrodes of the field effect transistors 25, 26 are connected to the outputs of a bistable multivibrator 27, which is supplied to terminal 28 by the ignition pulses for the converter valves is controlled. The output voltages of the two integration amplifiers 21, are combined in an adding amplifier 29 to form the mean value of the current. This current mean value is known via a Limiter stage - not shown - limited to a value, which corresponds to the current at the gap limit.

The formation of the current mean value during each current conduction period and its subsequent storage in the currentless pause by the integration amplifiers 21, 22 is controlled by the ignition pulses for the semiconductor valves of the converter. The ignition pulse for a valve sets, for example, the flip-flop 27 so that the field effect transistor 25 is permeable and the field effect transistor 26 is blocked. The integration amplifier forms the current-time integral of the current I and saves this value until the next ignition pulse. This controls the flip-flop 27 so that the feedback capacitor short-circuited and thus the integration amplifier: 22 cleared and the integration amplifier 22 is enabled. The storage of the mean current values in the integration amplifiers simplifies the dimensioning of the circuit.

6a shows the course of the actual current value I in the gap area. In Fig. 6b is the time course of the output signal L, of the averaging unit 20a.

Fig. 7 shows an embodiment with a correct sign - Acquisition of the actual current value in the DC circuit of the converter 2. The actual current value is measured via a

509830/0360

VPA 73/3228

function generator 30 designed as amount generator, its output signal from the limiting stage 31 between an upper and a lower limit value the same polarity is maintained, the upper limit value corresponding to the current value at the gap limit. The above the P ^ nktionsgeber 30 and the limitation stage 31 from the Current actual value I derived variable is used as a factor in the Multiplier 32 input, which is in the feedback of the operational amplifier 33 in the control differential amplifier 34 lies. The output signal of the puncture transducer 35, the is controlled by the puncture transmitter 30.

Pig. 8 shows the circuit diagram of a suitable puncture sensor 30 and a limiting stage 31 and Pig. 9 the Dependency of the output voltage U on the input voltage U of the puncture sensor of the Pig 8.

A suitable one for a control device according to the invention Puncture transmitter should correspond to the course of the loop gain as a function of the current in the gap area Have puncture. This relationship is in the already mentioned Siemens manual "Line-commutated power converters Thyristors "on pages 46-52 and 116-118. Purely for practical use, one can assume to a good approximation that the route gain in one Such a control loop in the gap area is proportional to the square of the current. A third link still appearing Order can be neglected in most applications. Accordingly, the output signal of the Puncture sensor 30 has an approximately quadratic dependence on its input signal. However, it did in many Applications have shown that a linear dependency also leads to sufficient results.

- 9 509830/0360

234433Q

VPA 73/3228

In Pig. 9 is the square puncture P through the straight line segments g1 and g2 as well as the straight line segments g3 and g4 which are symmetrical with respect to this are approximated. This can be done in a known manner by the in Pig. 8 shown diode matrix.

To limit the output signal of the puncture transmitter 30 to a lower limit value U min and to one

el -.

Limiter stage 31 is used for the upper limit value U max The midpoint of two high-value resistors 36 and 37 connected in series is the midpoint of two series connected diodes 38 and 39 connected. At the anode of the diode 38 is the voltage + U min and at the

The cathode of the diode 39 has the voltage + U max. The cons

Atands 36 and 37 must be sufficiently large against the potentiometer resistors be measured.

The upper limit value U max corresponds to the current at the Lüok border. The multipliers or dividers as elements for influencing the loop gain must be adjusted in this way be that their output signals match the associated input signals, if in each case at their second inputs the upper limit value U max is applied. In other words, this corresponds to a multiplication or Division by 1.

The lower limit value U min is chosen so that the loop gain even with very small currents in the gapable area is kept at an appropriate value in view of the errors of the dividers or multipliers.

According to a further embodiment of the invention, the peak value of the individual current pulses of the gap current can be used as the current value can be detected. This is possible because of the mean

- DQ)

503830/0360

VPA 73/3228

- 10 -

of the current in the Lüok area a puncture of the respective Maximum value and the steering angle.

Pig. FIG. 10 in conjunction with FIG. 11 shows a suitable one Peak value detection 40, which in a first approximation has the influence of the control angle are taken into account. The storage capacitor 41 is connected to the field effect transistor 42 as an electronic one Switch on the actual current value I at terminal 43. The actual current value I controls the operational amplifier 44 via the differentiating Input 45 at. The output signal of the operational amplifier 44 forms the control current i (FIG. 11b) for the field effect transistor 42. In the times in which a positive control current i flows, the transistor 42 is conductive and the Capacitor 41 is charged to the voltage at terminal 43 that maps the actual current value I. If the control current is zero or negative, the capacitor 41 retains the stored voltage until the next positive pulse of the control current i. A high-ohmic input resistance of the downstream circuit is necessary for this.

At terminal 46 there is a small voltage Uy for gate feed to ensure that transistor 42 is safely blocked even with current value UuIl in the gap area.

11a shows the course of the current I im over time Gap area, while in FIG. 11b the time profile of the control current i and in FIG. 11c the voltage profile IL., is shown on the capacitor 41, which corresponds to the respective peak value of the current pulses.

In the exemplary embodiment in FIG. 12, the current setpoint value I * becomes a variable for influencing the loop gain derived. The current setpoint I * acts on the substitute

- 11 509830/0360

VPA 73/3228

- 11 -

time element 47, which the transitional behavior of the control loop simulated in the event of a setpoint jump. The output signal of the equivalent timing element 47 is passed through the function generator 48, the output signal of which is the divider 49 in the signal input of the current regulator 5 is supplied as a divisor. To influence the time behavior of the current regulator 5 for adaptation the function converter 51, which also is acted upon by the function generator 48. The function converter 51 is on one in terms of wiring and optimization of the current regulator 5 suitable function is set.

Pig. 13 shows a particularly simply constructed exemplary embodiment the invention. The actual current value at the output terminal 7 of the three-phase current transformer 6 is via the limiting stage 52 is input to the divider 11 as a divisor, while the system deviation represents the dividends. The divider 11 is again adjusted so that at the upper limit value of the limit stage 52, the corresponds to the current at the gap limit, division by 1 takes place. In the non-gapping area above the The gap limit therefore no longer influences the loop gain.

19 claims
13 figures

- 12 -

509830/0360

Claims (17)

VPA 73/3228 - 12 claims J Control device for a controlled converter arrangement with a current regulator, a control set and a device for the gap current-dependent adaptation of at least one control loop parameter, characterized by a member for influencing the loop gain in constant dependence on a current value or a variable derived therefrom. 2. Control device according to claim 1, characterized in that the relevant current value or one derived therefrom Size is limited to an upper limit value that corresponds to the current at the gap limit, where the Member is balanced in such a way that the loop gain is only influenced below the upper limit value. 3. Control device according to claim 2, characterized in that that the relevant current value or a quantity derived therefrom is between an upper and a lower Limit value is kept the same polarity .. 4. Control device according to one of claims 1-3, that the instantaneous value of the actual current value is used as the current value (FIG. 13). 5. Control device according to one of claims 1-3, characterized in that the current mean value is used as the current value is used. 6. Control device according to claim 5, characterized by a smoothing element (12) acted upon by the actual current value for forming a mean current value (FIG. 1). - 13 509830/0360 VPA 73/3228 - 13 - 7. Control device according to claim 5, characterized by an averaging device (2Oa) with two of the current actual value (l) applied integration amplifiers (21, 22), whose feedback capacitors (23, 24) can be bypassed alternately by electronic switches (25, 26), their control electrodes with the outputs of one of the ignition pulses' controlled for the converter valves bistable multivibrator (27) are connected, the output voltages of the two integration amplifiers (21, 22) an adding amplifier (29) for forming an average current value are supplied (Fig. 5,6) 8. Control device according to one of claims 1-3, characterized in that the peak value of the current value Stromes is used. 9. Control device according to claim 8, characterized by a maximum value detection (40) with a storage capacitor (41) which can be switched to the actual current value (i) by an electronic switch (42), the actual current value (i) an operational amplifier (44) with a differentiating input (45) controls, the output signal of which affects the electronic switch (42) (Fig. 10, 11). 10. Control device according to one of claims 1-3, characterized characterized in that the output signal of the transition behavior as the variable derived from the current value The substitute timer (47), which simulates the control loop and is acted upon by the current setpoint value (I *), is used (Fig. 12). -H- 509830/0360 TPA 73/3228 -H- 11. Control device according to one of claims 1-3, characterized by one of the member for influencing the Circular amplification upstream puncture transmitter with a function of the course of the circular amplification function corresponding to the current in the gap area. 12. Control device according to claim 11, characterized in that the output signal of the puncture sensor in an approximately linear or quadratic dependence on its input signal. 13. Control device according to claim 11 with a correct sign Acquisition of the actual current value, characterized in that the puncture transmitter is designed as an amount generator is (Pig. 7). H. Control device according to claim 11, characterized by a smoothing element (H) in the input of the function generator (15) (Pig. 3). 15 · Control device according to claim 11, characterized by another puncture transducer (35, 51) controlled by the puncture transmitter (30, 48) for influencing the time behavior of the current regulator (5) (Pig. 7, Pig. 12). 16. Control device according to one of claims 1-15, characterized in that as a G-member for influencing the loop gain a divider (11, 49) is provided in the signal input of the current regulator (5), which is the dividend System deviation and as a divisor a current value or a size derived from this are entered (Pig. 1, Pig. 12) - 15 509830/0360 23U33G VPA 73/3228 - 15 - 17. Control device according to one of claims 1-15, characterized in that as a member for influencing the Circular amplification a divider (19) is provided in the output of the current regulator (5), which is used as the dividend Output voltage of the current regulator and a current value or a variable derived from it entered as a divisor are (Fig. 4). 13. Control device according to one of claims 1-15, characterized characterized in that a multiplier (16) in the feedback as a member for influencing the loop gain of the current control amplifier (17) is provided, at whose inputs the output signal of the current controller (18) and a current value or a quantity derived from it are present (Pig. 3). 19 · Control device according to one of claims 1 - 15, characterized characterized in that as a member for influencing the loop gain, a multiplier (32) in the Feedback of the control differential amplifier (33) provided at the inputs of which the system deviation and a current value or a variable derived from it are present (Mg. 7). 509830/0360