Drive controller for a self-commutated converter

This application claims the priority of German Patent Application, Serial No. 103 07 999.8, filed Feb. 25, 2003, pursuant to 35 U.S.C. 119(a)–(d), the disclosure of which is incorporated herein by reference.

The present invention relates to a drive controller for a self-commutated converter, and more particularly to a drive controller with a switched control circuit for the converter valves that can be dynamically and cyclically tested without interrupting service.

Great care must be exercised when using electric drives in industrial automation applications, for example with numerically controlled machine-tools and robots, to protect men and machine in the best possible manner. The electrical machine or the motor should be prevented from performing dangerous movements even when a single error occurs, by implementing a “safe stop” function for the motor. This function is typically initiated depending on the operating mode, e.g., before a protective door is opened.

The “safe stop” function is implemented by disconnecting the electric power at two places, for example, by also disconnecting the motor. It is generally accepted to separately disconnect the lower and/or upper converter valves of a self-commutated converter employing a bridge circuit.

A “safe stop” function can be implemented by “safely” blocking the control signals to the converter valves, which is referred to in the art also as “pulse inhibitor”, or to disconnect all converter valves.

The term “safely” is intended to indicate that the regulatory requirements imposed or suggested by the professional organizations or regulatory bodies for occupational safety are satisfied.

A conventional drive controller of this type is known from the German patent DE 100 59 173, as shown in detail in FIG. 1 . The self-commutated converter W has two half-bridges with converter valves T 1 , T 3 , T 5 , and T 2 , T 4 , T 6 , respectively. The drive controller has a separate control circuit for each half-bridge. Of the control circuits, only the associated opto-couplers OK 1 , OK 3 , OK 5 for the upper half-bridge, and OK 2 , OK 4 , OK 6 for the lower half-bridge are shown in FIG. 1 . The anodes of the photodiodes of the opto-couplers OK 1 , OK 3 , OK 5 and OK 2 , OK 4 , OK 6 are electrically connected with respective supply voltages SV 1 and SV 2 , whereas the cathodes are electrically connected with corresponding pulse inhibiting circuits I 1 and I 2 via resistors RS 1 , RS 3 , RS 5 , and RS 2 , RS 4 , RS 6 , and forward-biased diodes DS 1 , DS 3 , DS 5 , and DS 2 , DS 4 , DS 6 connected downstream of the resistors. The respective supply voltages SV 1 and SV 2 are present at corresponding outputs of pulse inhibiting paths IP 1 and IP 2 . Each of the pulse inhibiting paths IP 1 and IP 2 is connected to the supply voltage SV via a corresponding switch S 1 and S 2 , whereby the switches S 1 and S 2 receive control signals from associated pulse inhibiting circuits I 1 and I 2 . The pulse inhibiting path IP 1 and/or IP 2 is equivalent to a disconnectable power supply which is disconnected when a “safe stop” is triggered. The output side of each pulse inhibiting path IP 1 and IP 2 is connected to an associated pulse inhibiting circuit I 1 , I 2 via a diagnostic line which includes a decoupling diode, supplying corresponding diagnostic signals SV 1 _Diag and SV 2 _Diag to the pulse inhibiting circuits I 1 and I 2 .

The function “safe stop” is implemented by a pulse inhibitor which is used to switch off the converter valves T 1 to T 6 of the inverter W during normal operation or when a fault is detected. Preferably, the supply voltage SV 1 for the opto-couplers OK 1 , OK 3 , OK 5 for the upper bridge arm, which is derived from an external voltage SV, is interrupted by switch S 1 (either a mechanical or an electronic switch) by applying a signal IL 1 from the pulse inhibiting circuit I 1 . Another supply voltage SV 2 for the opto-couplers OK 2 , OK 4 , OK 6 for the lower bridge arm is interrupted by switch S 2 (either a mechanical or an electronic switch) by applying a signal IL 2 from the pulse inhibiting circuit I 2 , as well as by blocking the pulses in the control set ST.

The operation of the two pulse inhibiting paths IP 1 and IP 2 with the switches S 1 and S 2 can be checked cyclically and dynamically, for example each time after the supply voltage is switched on. For this purpose, the pulse controller I 1 reads the supply voltage SV 1 through the signal SV 1 _Diag, whereas the pulse controller I 2 reads the supply voltage SV 2 through the signal SV 2 _Diag, which are provided after the switches S 1 and S 2 , respectively. Even if one of the pulse controllers I 1 and I 2 fails, the other properly operating pulse inhibiting controller I 2 or I 1 can still respond, since the aforedescribed forced dynamical operation can detect even so-called dormant errors.

Disconnectable paths have to be tested for errors, since the probability of a component failure is never zero. As mentioned above, the function “safe stop” requires two redundant disconnectable paths which are checked at predefined test intervals, for example every eight hours. This guarantees the required protection against single faults. However, the operation of the device must be interrupted for the test, which makes more frequent tests of the disconnectable paths impractical.

It would therefore be desirable and advantageous to improve the disconnectable voltage supplies of conventional drive controllers by obviating prior art shortcomings, so that the switches of converters can be tested more frequently and at arbitrary time intervals without service interruption.

According to one aspect of the present invention, a drive controller for a self-commutated converter comprised of two half-bridges with converter valves includes two control circuits, wherein each control circuit is associated with a corresponding half-bridge and operatively connected with the converter valves of that half-bridge; first switches that are connected between a voltage supply and each of the control circuits for switchably connecting the control circuits to an external voltage; second switches that are connected electrically in parallel with the first switches in one-to-one correspondence, wherein the corresponding connected first and second switches are decoupled from each other by decoupling diodes; and controllers providing control signals to the connected first and second switches so as to alternatingly switch the connected first and second switches on and off.

By connecting a second switch electrically in parallel with each first switch and decoupling these parallel connected switches from each other by decoupling diodes, the switches can be alternatingly switches on and off and the operation and functionality of the switches can be tested without service interruption. For this purpose, the voltage at the output of each switch is measured. If one switch is disconnected for testing, the voltage is maintained in the subsequent control operation through the parallel closed path. As a result, the switches operate dynamically without service interruption.

According to another aspect of the invention, a drive controller for a self-commutated converter comprised of two half-bridges with converter valves includes two control circuits wherein each control circuit is associated with a corresponding half-bridge and operatively connected with the converter valves of that half-bridge; a circuit assembly having an output supplying a DC voltage to the control circuits; switches connected between an external voltage and an input of the circuit assembly; and controllers providing control signals to the switches so as to control the switches in a pulsed operating mode.

A common circuit assembly for supplying a DC voltage is connected after the two switches, which ensures that the supply voltage for the control circuits is not affected by testing of the input-side switches. Since these switches can be operated by clock pulses, these switches can always be tested exactly at the time when the switch is turned off.

Both embodiment of the disconnectable voltage supply have in common that the switches are continuously switched on and off while the converter is operating, without causing voltage changes at the supply inputs of the control circuits connected downstream. The state of each switch can hence be checked without service interruption, so that a forced dynamic operation without service interruption is obtained.

Embodiments of the invention may include one or more of the following features. A first set of the decoupled first and second switches can be electrically connected in series with a second set of decoupled first and second switches, so that the series connection of these two sets connects the control circuits to an external voltage. The drive controller can include two circuit assemblies, with each circuit assembly supplying a separate DC voltage to the control circuits of each half bridge, and with each switch providing the external voltage to an input of one of the circuit assemblies that is operatively connected with the respective switch. The circuit assembly supplying the DC voltage can include a rectifier, and a potential separation device can be connected before the rectifier and a support capacitor can be connected to an output of the rectifier. The potential separation device can be a coupling unit, for example, an inductive element such as a transformer, or a capacitive element.

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a block circuit diagram of a conventional drive controller having the function “safe stop”;

FIG. 2 is a first variant of a first embodiment of the drive controller according to the invention;

FIG. 3 is a second variant of the first embodiment of the drive controller according to the invention;

FIG. 4 is a first variant of a second embodiment of the drive controller according to the invention; and

FIG. 5 is a second variant of the second embodiment of the drive controller according to the invention.

Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIGS. 2 to 5 , there are shown block circuit diagrams of different embodiments of a drive controller according to the invention. However, unlike in the block circuit diagram of FIG. 1 , the self-commutated converter W and the motor are not shown in FIGS. 2 to 5 for sake of clarity.

FIG. 2 shows in greater detail a first variant of a first embodiment of the drive controller AA according to the invention. The switches S 1 A and S 2 A are equivalent to the switches S 1 and S 2 in FIG. 1 . However, unlike the conventional drive controller A depicted in FIG. 1 , the disconnectable power supply that controls the control circuit for the converter valves T 1 , T 3 , T 5 , and T 2 , T 4 , T 6 , respectively, of the free running converter W depicted in FIG. 2 includes in addition a second switch S 1 B that is electrically connected in parallel with the switch S 1 A, and a second switch S 2 B that is electrically connected in parallel with the switch S 2 A. The corresponding switches S 1 A and S 2 A, and S 1 B and S 2 B, which are connected in parallel, are decoupled from each other by respective decoupling diodes D 1 A, D 1 B and D 2 A, D 2 B. The inputs of the parallel paths receive a common external voltage SV. The corresponding outputs of the parallel paths provide supply voltages SV 1 and SV 2 for the corresponding sets of opto-couplers OK 1 , OK 3 , OK 5 and OK 2 , OK 4 , OK 6 , that control the control circuits for the associated sets of converter valves T 1 , T 3 , T 5 , and T 2 , T 4 , T 6 , respectively. The outputs of the switches S 1 A and S 1 B, and/or S 2 A and S 2 B, supply diagnostic signals SV 1 A_Diag and SV 1 B_Diag, and SV 2 A_Diag and SV 2 B_Diag, respectively. The controllers I 1 and/or I 2 apply switching signals IL 1 A and IL 1 B, and/or IL 2 A and IL 2 B, to the switches S 1 A and S 1 B, S 2 A and S 2 B. The controllers I 1 and I 2 in the conventional embodiment of FIG. 1 are also referred to as pulse inhibiting controllers I 1 and/or I 2 that control the switches S 1 and S 2 of the pulse inhibiting path IP 1 and IP 2 , thereby forming a disconnectable power supply.

Referring again to FIG. 2 , the switches S 1 A and S 1 B, and S 2 A and S 2 B, respectively, must be controlled in an alternating fashion for performing a cyclical test and a forced dynamic operation. As a result, one path of each disconnectable voltage supply is always closed, whereas the associated parallel path is open. The switching operation of each switch is tested by measuring the associated diagnostic signals SV 1 A_Diag, SV 1 B_Diag, SV 2 A_Diag, and SV 2 B_Diag. If at least one of the diagnostic signals SV 1 A_Diag, SV 1 B_Diag, SV 2 A_Diag, and SV 2 B_Diag is different from zero, then this indicates a fault in the switching operation, causing the self-commutated converter W to switch off.

FIG. 3 shows in greater detail a second variant AB of the drive controller depicted in FIG. 2 . In FIG. 3 , the disconnectable power supplies in second variant are each connected with both control circuits, and not just with one control circuit, as in FIG. 2 . The two disconnectable power supplies of the first variant are here electrically connected in series. In spite of the series connection of two disconnectable voltage supplies, the switches S 1 A and S 1 B and S 2 A and S 2 B can still be cyclically tested by alternatingly operating the switches S 1 A and S 1 B and S 2 A and S 2 B, respectively. The switches S 1 A and S 1 B and S 2 A and S 2 B are switched synchronously so that one path is always closed. This circuit also works if the two disconnectable power supplies that are electrically connected in series share a single voltage supply. In other words, one of the two voltage supplies that are electrically connected in parallel can be eliminated in the switching assembly depicted in FIG. 3 .

FIG. 4 shows in greater detail a first variant of a second embodiment of the drive controller AC according to the invention. A circuit assembly VG 1 with a rectifier G 1 that supplies DC power is connected downstream of the two switches S 1 and S 2 . A potential separation device A 1 is connected to the input of the rectifier G 1 , and a support capacitor C 1 is connected to the output of the rectifier G 1 . The potential separation device A 1 can be either an inductive or a capacitive coupling unit. The inputs of both switches S 1 and S 2 are connected in common to an external voltage SV. Like in the conventional drive controller A of FIG. 1 , each output of the switches S 1 and S 2 supplies a diagnostic signal SV 1 _Diag, SV 2 _Diag to a corresponding controller I 1 or I 2 . (see FIG. 1 )

The two switches S 1 and S 2 do not perform a simple switching function, as in the conventional embodiment of the drive controller A of FIG. 1 , but are pulsed. More particularly, the switches in this variant AC are pulsed in a push-pull mode. A pulsed voltage (AC value) is then generated at the output of the switches S 1 and S 2 , which is transmitted to the rectifier G 1 at a different potential. The output of rectifier G 1 provides the supply voltage SV 1 for the two control circuits. The voltage SV 1 supplied by the rectifier G 1 is smoothed by the support capacitor C 1 before being used as a supply voltage.

Each time one of the two switches S 1 and S 2 that is pulsed in a push-pull mode is switched off, the switching operation of each switch S 1 , S 2 is tested by analyzing the diagnostic signal SV 1 _Diag, SV 2 _Diag. When a tested switch S 1 and/or S 2 operates properly, the corresponding diagnostic signal SV 1 _Diag or SV 2 _Diag is zero. If a fault is detected, the signal is different from zero.

With this embodiment, a short-circuit at a switch can advantageously be detected even when the self-commutated converter W is operating. For this purpose, a diagnostic short-circuit signal K is measured at the potential separation unit A 1 , for example, by measuring a current flowing in the potential separation unit A 1 . In the event that this current goes to zero, indicating a short-circuit or an open circuit, the voltage for the opto-couplers OK 1 to OK 6 can still be supplied by the support capacitor C 1 .

FIG. 5 shows in greater detail a second variant of the second embodiment of the drive controller AD according to the invention. This variant is different from the first variant AC of FIG. 4 in that it includes a second switching assembly VG 2 that is identical to the first switching assembly VG 1 . The second switching assembly VG 2 also supplies a DC voltage. An input of the second switching assembly VG 2 is connected to the switch S 2 , and the output of the second switching assembly VG 2 is connected to the control circuit for the converter valves T 2 , T 4 , T 6 of the lower half-bridge of the self-commutated converter W. Accordingly, each of the two control circuits includes a disconnectable voltage supply according to the invention which enables cyclical testing of the switching operations of the switches S 1 and S 2 without service interruption. In other words, one achieves a forced dynamic mode without a service interruption.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.