AT512886B1 - Method and device for adjusting the delay time of a semiconductor valve - Google Patents

Abstract

The invention relates to a method and a device for adjusting the delay time of at least one semiconductor valve (7a, 7b, 7c) of a parallel converter circuit (1a, 1b, 1c) when the ignition angle between two conducting periods of the semiconductor valve changes. To achieve the most uniform possible distribution of current to all the parallel-connected semiconductor valves (7a, 7b , 7c), it is provided that, after changing the ignition angle, a new delay time is given which results from the old delay time Δta before the change of the ignition angle, from the old ignition angle αa and from the new ignition angle αn: Δtn = Δta * sin ( .alpha..sub.a) / sin (.alpha..sub.n).

Description

Austrian Patent Office AT512 886B1 2014-03-15

description

METHOD AND DEVICE FOR ADJUSTING THE DELAY TIME OF A SEMICONDUCTOR VALVE

TECHNICAL AREA

The invention relates to a method for adjusting (pilot control) of the delay time of at least one semiconductor valve of a converter parallel circuit when changing the ignition angle between two periods of the semiconductor valve, and a corresponding device. The parallel converter circuit comprises at least two semiconductor valves connected in parallel between an alternating current or three-phase connection on the one hand and a direct current connection on the other. As semiconductor valves, for example, thyristors, IGBTs or GTOs are used. The semiconductor components may have a positive as well as a negative temperature characteristic. The invention is particularly applicable to semiconductor valves in rectifiers of excitation systems for synchronous machines, wherein a plurality of rectifiers are connected in parallel.

The firing angle of a semiconductor valve describes the difference between the zero crossing of the AC voltage to be rectified by the semiconductor valve, and the time of ignition of the semiconductor valve based on the present at this time phase position of the AC voltage. The ignition angle is used to adjust the output voltage of the converter.

A change in the ignition angle between two conducting periods of the semiconductor valve is also referred to as Zündwinkelsprung. This Zündwinkelsprung can be predetermined for example by the control of the synchronous machine. When a spark angle jump occurs, it causes a changed applied voltage at the commutation inductance. A commutation or commutation inductor causes a delay of the current increase in the turn-on of the semiconductor valve. Too high a rate of current rise could destroy the silicon structure of the semiconductor valve. The change in the applied voltage at the commutation inductance also alters the steepness of the temporal current profile.

There may be large Zündwinkelsprünge of more than 10 °, such as by shock excitation due to a change in the load of the synchronous machine, where Zündwinkelsprünge of several 10 °, about 40-70 °, are not uncommon. By large Zündwinkelsprünge it comes with so-called balanced systems to large current deviations. In balanced systems, several semiconductor valves are connected in parallel and each semiconductor valve supplies approximately the same current.

A control method for such a balanced system is known for example from AT 509 828 A1. The current distribution of parallel-connected branches of semiconductor valves depends primarily on the semiconductor parameters, the thermal conditions and parasitic influences, such as the stray inductances of a system. According to AT 509 828 A1, in each case a partial flow flowing through the respective semiconductor valve is detected over a period of time and supplied to a symmetry control. For each of these detected partial flows, a mean value is formed and from the resulting average values, the actual current and the common ignition angle, a respective ignition angle correction is derived for each semiconductor valve, so that the loads on the semiconductor valves are approximated. Thus, there is an active current balancing, in which the firing pulses of the parallel-connected semiconductor valves are temporally shifted by the type of control so that each parallel branch leads approximately the same load current. By staggered ignition (time offset in the microsecond range) so the current transfer of the individual valves is influenced so that, if necessary, even without compensating reactors and without symmetrical busbar or parameter selection, the parallel branches can be uniformly loaded. A spark angle jump now causes deviations from the symmetrical current distribution to occur in all semiconductor valves. These deviations may even be worse in the worst case than if all the semiconductor valves ignite simultaneously.

If a commutation inductance is provided, then the smaller the voltage at the commutation inductance, the lower the current gradient of the overall system, and therefore the required delay time, which is required for a symmetrical current split, is greater.

STATE OF THE ART

From EP 0 664 613 A2 a method for balancing the load of parallel connected power semiconductor modules is known, where the switch-on and switch-off of the switches of the modules are set so that a uniform current distribution results when switching to all modules. In this case, about a module can be turned on later, if the difference between the setpoint and actual value of the current is negative, so the actual current is greater than the target current.

However, EP 0 664 613 A2 does not specify the extent to which the switching time must shift.

PRESENTATION OF THE INVENTION

It is therefore an object of the present invention to provide a method with which the time of ignition of at least one semiconductor valve is set in advance when changing the ignition angle between two periods so that the most uniform possible current distribution to all parallel-connected semiconductor valves continues to be given.

This object is achieved by a method having the features of patent claim 1. Advantageous embodiments of the invention are defined in the respective dependent claims.

Claim 1 relates to a method for adjusting the delay time of at least one semiconductor valve of a converter parallel circuit when changing the firing angle between two periods of the semiconductor valve and provides that after changing the firing angle a new delay time is given, resulting from the old delay time Ata before the Change in the firing angle, from the old firing angle aa and from the new firing angle, is as follows: Atn = Ata * sin (aa) / sin (an). The new delay time is therefore the product of the old delay time and the quotient of the sine of the old ignition angle and the sine of the new ignition angle.

In simulations has been confirmed that with the inventive method after a Zündwinkelsprung and after changing the delay time again an at least approximate symmetry of the currents in the individual semiconductor valve branches of the converter, in particular the rectifier, can be produced.

A power converter parallel circuit usually has two to eight power converters connected in parallel, in the case of excitation systems rectifier on. Each power converter in turn has a plurality of semiconductor valves, two per phase. In this case, only a semiconductor valve or a phase generally has no delay time. For all other semiconductor valves with delay time, it makes sense that a new delay time is given. It can thus be provided that, in the case of a plurality of semiconductor valves connected in parallel, a new delay time is predetermined for all semiconductor valves, which have a delay time before the ignition angle is changed.

There is also the possibility of setting a new delay time to reduce the control effort only for larger changes for one or more semiconductor valves. For example, it may be provided that a new delay time is calculated only after a change in the ignition angle of more than, for example, 10 °. A corresponding device according to the invention comprising a parallel converter circuit with a plurality of parallel-connected semiconductor valves and a control device for adjusting the delay time of at least one semiconductor valve provides for carrying out the method according to the invention that with the control device according to Change of the ignition angle, a new delay time can be predetermined, which results from the old delay time Ata before the change of the ignition angle, from the old ignition angle aa and from the new ignition angle as follows:

Atn = Ata * sin (aa) / sin (an).

Since the control of the semiconductor valves and the calculation of the new delay times of the semiconductor valves is usually carried out by means of an electronic data processing system, so a computer, the invention also includes a computer program with program code means to perform the inventive method, when the computer program is running on a computer. Accordingly, a computer program product is also provided, comprising program code means of a computer program stored on a computer-readable data carrier in order to carry out the method according to the invention when the computer program is executed on a computer.

BRIEF DESCRIPTION OF THE FIGURES

To further explain the invention, reference is made in the following part of the description to the figures, from the further advantageous embodiments, details and further developments of the invention can be found. 1 shows a basic circuit of three rectifiers, FIG. 2 shows the circuit construction of the three rectifiers from FIG. 1 to which the method according to the invention can be applied, FIG [0022] FIG. 4 shows a diagram of the current profile of three semiconductor valves after a positive ignition angle jump without setting the delay time according to the invention, [0023] FIG. 5 shows a diagram of the current profile of three semiconductor valves after the positive ignition angle jump with inventive adjustment of FIG 6 shows a diagram of the current profile of three semiconductor valves after the positive ignition angle jump with ideal setting of the delay time. FIG. 7 shows a diagram of the current profile of three semiconductor valves after a negative ignition angle jump without a setting of the delay time according to the invention, [0026] FIG 8 is a diagram of the current course of three semiconductor valves after the negative Zündwinkelsprung with inventive adjustment of the delay time.

EMBODIMENT OF THE INVENTION

To supply a load 2, for example, an exciter circuit of a generator, in Fig. 1 to a supply network 3 via a mains connection 5 and a transformer 4, for example, three power converters 1a, 1b, 1c connected in parallel. For each rectifier 1a, 1b, 1c, a commutation inductance (commutation inductor) 6a, 6b, 6c is provided, which limit the current changes (di / dt values) of the branches connected in parallel in the time interval of the current commutation.

In Fig. 2 is simplified excitation system for synchronous machines with three parallel rectifiers 1a, 1b, 1c to see from Fig. 1, namely the training of the rectifier in each case as a so-called B6 bridge. On the DC side, a load 2 is connected to the rectifiers 1a, 1b, 1c. On the AC side, the power converters 1a, 1b, 1c are connected to three phases. Accordingly, each power converter 1a, 1b, 1c comprises six semiconductor valves 7a, 7b, 7c. The rectified current of each B6 bridge is fed to a common line, which then feeds load 2, a field winding of the synchronous machine. Each semiconductor valve 7a, 7b, 7c is supplied by a control device 9, a control voltage which defines both the time of ignition and the ignition angle.

The processes are explained with reference to the three semiconductor valves 7a, 7b, 7c, which ignite during a positive voltage of the first phase 8a, that is, which are arranged in the positive current branch of the first phase 8a. A partial flow 1a, 1b, 1c flows through each of these semiconductor valves 7a, 7b, 7c. The three semiconductor valves 7a, 7b are ignited according to a symmetry control, such as that of AT 509 828 A1, at different times. Due to the time-delayed ignitions, the power converters 1a, 1b, 1c have approximately the same load.

The Symmetrieregelung carried out by determining the current deviations of the partial streams 1a, 1b, 1c from the average. The current deviations form the input variables for the actual balancing control. The respective current deviation is supplied, for example, to a respective integral controller. To obtain a Zündwinkelkorrektur the respective resulting control value is converted into a delay time. In this case, the common ignition angle and the actual current value are taken into account. This delay time is then forwarded via the control device 9 to each of the eighteen semiconductor valves 7a, 7b, 7c here, so that they ignite at the predetermined time. In FIG. 2, for the sake of simplicity, only the connection of the control device 9 with the rectifiers 1a, 1b, 1c is shown.

The control device 9 comprises a computer, which now according to the invention at a Zündwinkelsprung from the predetermined values of the old delay time (s) Ata before the change of the ignition angle, the old firing angle aa and the new firing angle to the new (n) delay time (en ).

In FIGS. 3-8, the current profile of three semiconductor valves 7a, 7b, 7c is shown over time. On the horizontal axis, the time is plotted in milliseconds, each representing about 7 milliseconds. On the vertical axis, the current is plotted in amperes, ranging from 0 to a maximum of 250 amps.

Fig. 3 shows the current flow of three semiconductor valves 7a, 7b, 7c before a Zündwinkelsprung according to a simulation calculation. The current Ia, Ib, Ic after each semiconductor valve is plotted here as a function of time during a conducting period of the semiconductor valve. In this starting position all three currents are on average the same over time, ie symmetrical, there is a symmetrized system. The first semiconductor valve 7a provides a time average of 132.1A for Ia, the second semiconductor valve provides 132.2A for Ib and the third semiconductor valve 132.6A for Ic.

In this case, the first semiconductor valve 7a starts with a delay time of 216 ps and the second semiconductor valve 7b with a delay time of 50 ps. The third semiconductor valve 7c has no delay time. The current (old) ignition angle aa is 30 ° for all semiconductor valves.

What happens when the ignition angle jumps without precontrol (adjustment) of the delay time from 30 ° to 87 °, is shown in Fig. 4: The first semiconductor valve 7a delivers only 124.5 A as la, the second semiconductor valve only delivers 124.1 A as Ib and the third semiconductor valve 144.3 A as Ic. Due to the delay of the individual semiconductor valve branches would not be guaranteed in the real case that the first semiconductor valve 7a also ignites, because at the time of ignition, the commutation, ie the transition of the current flow to another semiconductor valve branch is already completed.

However, if the first semiconductor valve 7a does not fire, the second 7b and the third semiconductor valve 7c are extremely overloaded, which would lead to shutdown of them or even destruction. Therefore, according to the present invention, the delay time of the first semiconductor valve becomes 0.000216 sec

Atn = 0, 000216 * sin (30 °) / sin (87 °) = 0, 000108 s (108 ps) changed. 4/13 Austrian Patent Office AT512 886B1 2014-03-15 The delay time of the second semiconductor valve 7b is then 15 με according to the invention. It can be seen from FIG. 5 that the current Ia of the first semiconductor valve 7a in the conduction period is 134.8 A, that of the second semiconductor valve is 130.4 A and that of the third semiconductor valve 131.5 A. Thus, again, there is an approximately symmetrical system in front.

As can be seen from FIG. 6, a delay time of 114 με for the first 7a and 24 με for the second semiconductor valve 7b would be necessary for an ideally balanced system. Then, the current Ia of the first semiconductor valve in the conduction period would be 132.3 A, that of the second semiconductor valve 131.4 A and that of the third semiconductor valve 131.9 A.

FIGS. 7 and 8 show a further example of the method according to the invention. It starts from the fully balanced system in FIG. 6 where the firing angle is 87 ° and the delay times for the first semiconductor valve 7a are 114 ps and for the second semiconductor valve 7b 24 ps. In Fig. 7 shows what happens when the firing angle of 87 ° without precontrol (adjustment) of the delay time jumps back to 30 °. The first semiconductor valve 7a now supplies 152.9 A as La, the second semiconductor valve 7b supplies 126.6 A as Ib and the third semiconductor valve 7c only 117.4 A as Ic. There is thus a large imbalance, which can again lead to destruction or shutdown of the semiconductor valves 7a, 7b, 7c.

However, when the delay times are changed according to the invention, namely to 228 ps for the first semiconductor valve 7a and 48 ps for the second semiconductor valve 7b, the result is current waveforms as shown in Fig. 8. The first semiconductor valve 7a now supplies on average 130.2 A as la during a conducting period, the second semiconductor valve 7b supplies 134 A as Ib and the third semiconductor valve 7c as 132.5 A as Ic. Again, there are almost perfectly balanced semiconductor valve branches.

Of course, what has been described here only for one half-wave of a phase 8a is carried out in the same way for the respective second half-wave and for all other phases 8b, 8c using the same control device 9. REFERENCE LIST: 1a first rectifier 1b second rectifier 1c third rectifier 2 load 3 supply network 4 transformer 5 grid connection 6a first commutation inductor 6b second commutation inductor 6c third commutating inductor 7a first semiconductor valve 7b second semiconductor valve 7c third semiconductor valve 8a first phase 8b second phase 8c third phase 9 controller la first Partial flow Ib second partial flow Ic third partial flow 5/13

Claims (7)

Austrian Patent Office AT512 886B1 2014-03-15 Claims 1. A method for adjusting the delay time of at least one semiconductor valve (7a, 7b, 7c) of a parallel converter circuit (1a, 1b, 1c) when the ignition angle between two conducting periods of the semiconductor valve is changed, characterized in that after changing the ignition angle, a new delay time is given which results from the old delay time Ata before the change of the ignition angle, from the old ignition angle aa and from the new ignition angle as follows: Atn = Ata * sin (aa) / sin (an ). 2. The method according to claim 1, characterized in that at a plurality of parallel semiconductor valves (7a, 7b, 7c) for all semiconductor valves (7a, 7b), a new delay time is given, which have a delay time before changing the ignition angle. 3. The method of claim 1 or 2, characterized in that only from a change in the ignition angle of more than 10 °, a new delay time is calculated. 4. Apparatus for carrying out a method according to one of claims 1 to 3, comprising a parallel converter circuit (1a, 1b, 1c) with a plurality of parallel-connected semiconductor valves (7a, 7b, 7c) and a control device (9) for adjusting the delay time of at least one semiconductor valve , characterized in that with the control device (9) after changing the ignition angle, a new delay time can be predetermined, which results from the old delay time Ata before the change of the ignition angle, from the old ignition angle aa and from the new ignition angle as follows: Atn = Ata * sin (aa) / sin (an). A computer program comprising program code means for performing the method of any one of claims 1 to 3 when the computer program is run on a computer. A computer program product comprising program code means of a computer program stored on a computer-readable medium for carrying out the method according to one of claims 1 to 3 when the computer program is executed on a computer. For this 7 sheets drawings 6/13