GB2137832A - Control Means for a Power Converter - Google Patents

Abstract

Control means for a power-converter WR enables automatic testing of the operational readiness of the converter for parallel operation with other converters (not shown) at a common load rail S. A control unit 1 controls and monitors operation of the converter, a control unit 2 regulates the output power via unit 1, and a control unit 3 tests the readiness for parallel operation. Following preliminary testing of the control, monitoring and power regulating functions of units 1, 2, signals on lines 101, 102 cause unit 3 to effect the parallel operation readiness test. Unit 3 causes units 1 and 2 to first control converter WR to give a higher than nominal output and this is checked by a voltage monitor SpW resulting in an acknowledge signal on line 106. Units 1 and 2 are then caused to operate converter WR at a lower than nominal voltage, resulting in an acknowledge signal on line 107. If both signals 106, 107 are obtained, a contact K3 is closed to connect converter WR to line S. Absence of either or both of signals 106, 107 indicates unreadiness for connection and the converter is de-energised via AND gate 3/5 and line 108 when a timer 3/1 of unit 3 times out. <IMAGE>

Description

SPECIFICATION Control Means for a Power Converter The present invention relates to control means for a power converter and has particular reference to circuit means for testing the operational readiness of a power converter for parallel operation with other converters at a load collecting rail, in which circuit means are provided means for the testing of control and monitoring functions as well as regulating functions for the power control for the parallel operation. Circuit means of that kind for power regulation of converters operated in parallel and for monitoring the power control is described in the specification of German (Fed. Rep.) patent Application P 32 42 993.2.Such converters are employed in the field of electrical alternating current supply systems, the system comprising two or more power converters which are operated in parallel and of which individual ones can be switched as required into and out of the parallel combination.

Serving for the testing of the control and monitoring functions in circuit means of the stated kind are means which operate in conjunction with separate control units which are associated with each converter, namely a respective control unit for the control of the converter and monitoring of the output magnitudes thereof and a respective power control unit with an appropriately constructed regulating circuit.

Such tests are performed after the starting of a converter, that is to say after the connection thereof to the operating voltage before the converter concerned is switched into the parallel combination.

In order to prevent a converter, which is defective for the parallel operation, from then being switched into the parallel combination and thereafter switched off through the tested monitoring means, the parallel operation readiness of a power converter has hitherto been manually tested with the use of further switching elements for the circuit means, inclusive of switching means. In practice, however, this functional testing was performed only in the case of a defective converter, which required special knowledge of the operator and an expenditure in switching elements, as mentioned, for the circuit means.

It would thus be desirable for the testing of the parallel operation readiness of a power converter to be performed after the switching-in thereof without appreciable additional cost and automatically, securely and insensitively to interference.

According to the present invention there is provided control means for a power converter connectible at output means thereof by way of switching means to a load collecting rail to operate in parallel with at least one further such converter connected to the rail the control means comprising a first control unit to control and monitor operation of the converter, a second control unit to regulate the power of the converter by way of the first control unit, and a third control unit so connected at input means thereof to the first control unit and the switching means and at output means thereof to the first and second control units as to be operable, in response to application of voltage to the converter and after testing of the control, monitoring and regulating functions of the first and second control units has been performed, to test in a predetermined sequence of steps the operational readiness of the converter for connection to the rail.

The third control unit thus functions for automatic testing of the parallel operation readiness of the power converter after preceding testing of the control and monitoring functions as well as of the regulating function, the third control unit being disposed in effective connection through inputs and outputs with the first control unit as well as with the switching means at the output of the converter and also in effective connection through a further output with the second control unit.

Preferably, the second unit is connected at input means thereof to output means of a first and a second transformer which are serially connected by primary windings thereof between the converter output means and the switching means to sense the values respectively of the output current and the output voltage of the converter, the first control unit is arranged to set the value of the output voltage of the converter in dependence on a regulating signal from the second control unit and to control connection of the converter to the rail by way of the switching means and comprises a voltage monitor connected to the output means of the second transformer to monitor the value of the converter output voltage and to provide a first and a second output signal when such value is respectively above and below a nominal value, and the third control unit comprises a third transformer connected at input means thereof to the converter output means, a change-over switch settable to cause and resettable to terminate application of drive signals to the second control unit, one of the drive signals being provided by the output voltage of the third transformer fed through a secondary winding of the first transformer and the second control unit being so operable in response to the application thereto of such drive signals as to deliver a regulating signal to initially cause the converter output voltage to be set to a value above the nominal value, a polarity reversing switch operable to reverse the polarity of the output voltage of the third transformer thereby to so influence the regulating signal as to cause the converter output voltage to be reset to a value below the nominal value, first timing means actuable by a signal supplied by the first control unit to provide a first timing signal, second timing means so actuable by a further signal supplied by the first control unit and indicative of determined operational readiness of the first and second control units as to provide a second timing signal to cause the changeover switch to be set and the first control unit to control the switching means for interruption of the connection of the converter to the rail, a first trigger device actuable by the first output signal of the voltage monitor to effect said operation of the polarity reversing switch, a second trigger device actuable by the second output signal of the voltage monitor to control the second timing means to terminate the second timing signal thereby to cause the change-over switch to be reset and the first control unit to control the switching means for connection of the converter to the rail, and an AND-gate to interlink the first and second timing signals in the absence of either or both of the first and second output signals of the voltage monitor so as to provide a signal to cause the first control unit to control the switching means for interruption of the connection of the converter to the rail.

By means of this third control unit, the regulating loop for the parallel connection of equally or differently dimensioned power converters can be tested for operational readiness after each switching-in of the associated converter, even if this is operated as an individual current source.

Control means embodying the invention may have the advantage that no appreciable effort in switching circuit elements and switching devices is necessary for control means including such a third control unit, as the circuit elements for cooperation therewith are in any case present in the other control units and the associated converter, for example elements such as respective transformers detecting converter output current and output voltage, a voltage monitor and the switching means for connecting the converter to the rail.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of control means associated with a power converter, the control means embodying the present invention; and Figs. 2A and 2B are diagrams illustrating signals of components of the control means.

Referring now to the drawings, there is shown in Fig. 1 a power converter WR illustrated in the form of a block. The output of the converter WR is connectible through a line L with a parallel switching contactor K3-the connection being made by closing of the contactor-to a collecting rail S for the load, to which rail several converters (not shown) are individually connectible for parallel operation one-with the other.The line L includes the primary windings Qf two transformers, namely a transformer ü 1 1 detecting the actual value of the output voltage u, and a current transformer ü2 detecting the actual value of the output current i, by which the converter is loaded, both transformers being used for the purpose of voltage and current regulation or the regulation of the real power delivered by the converter WR.

Associated with the converter WR is control means comprising a control unit 1, which directly effects the control of the converter and upstream of which, through an input 105, is arranged a regulator 2/3 as a component of a further control unit 2. The control unit 1 includes a voltage monitor SpW for the output voltage u, which is fed through an input 1 1 2t of the control unit 1.

The output voltage u of the converter WR is at the same time fed through an input 112 to power direction recognition means 2/1 as a component of the control unit 2, the actual value of the output current i of the converter also being fed to the recognition means 2/1 by way of a second input 110.

The control unit 2 also includes a differential amplifier 2/2, the output of which is connected with the input of the regulator 2/3 and to the two inputs of which, designated by + and-, is fed a reference voltage A, which is formed by the output voltage of the power direction recognition means 2/1 constructed as a real power actual value transmitter and the voltage Uss at a common control collecting rail, designated by SS, of power converters operating in parallel combination on a load collecting rail S. The voltage U55 represents the "mean value" of the control voltage of all power converters operating on the rail S and forms the target value for the real power regulation of the converter WR and parallel operation with the converters operating on the rail S.

The control means also comprises, apart from the control units 1 and 2, a third control unit 3, which stands in effective connection through a number of inputs and outputs with the control units 1 and 2 as well as with the line L. All inputs and outputs of the control unit 3, the outputs and inputs of the control units 1 and 2 connected therewith, and the connecting lines concerned inclusive of a report line emanating from the line L and from the contactor K3, respectively, are provided with the same reference numerals.

Accordingly, the mentioned input of the controlunit 1, which is connected with the output of the regulator 2/3 of the control unit 2, and the output concerned of the unit 2 as well as the connecting line concerned, are designated by 1 05.

The control unit 3 at the input side comprises two timing members 3/1 and 3/2, a voltage transformer 3/ill with a secondary winding switchable over by means of a polarity reversing switch 3/K2, and two acknowledging storage members 3/3 and 3/4. At the output side, the control unit 3 comprises a change-over switch 3/K1 and an AND-member 3/5, which is arranged downstream of the timing members 3/1 and 3/2.

The components are intended for certain functions within the scope of the testing of the readiness of the converter WR for parallel operation with other power converters, which functions are each to be performed before switching of the converter WR into parallel combination with the otherconverters;These functions are brought into effect in a programmed time sequence of individual operations proceeding automatically.The parallel operation readiness test with these individual operations are preceded by preliminary tests, which are performed as hitherto and are initiated after the switching-in, i.e., after the connecting of the converter WR to operating voltage, initially the testing of the control and monitoring means of the converter (control unit 1), inclusive of the voltage monitor SpW, and thereafter testing of the regulating circuit for the power control (control unit 2). A positive result of these tests, that is to say ascertaining that the mentioned control and monitoring means as well as the regulating circuit for the power control are sound and thus ready for use, is prerequisite to performance of the additional and, at the same time, concluding testing by means of the control unit 3.

The readiness for use of the control and monitoring means as well as of the regulating circuit for the power control of a converter is signalled by formation of a signal at the output 102 of the control unit 1, which signal is fed to the corresponding input 1 02 of the control unit 3.

As a result, the timing member 3/2 is set into motion and the mentioned functions of the control unit 3 are thereby brought into effect.

Through a signal at the output 101 of the control unit 1, previously formed during the switching-in of the converter, the timing member 3/1 is set into motion. Both timing members are, for example, monoflops with certain selected resetting times (running times).

Through the timing member 3/2 set into motion, the change-over switch 3K/1 is actuated for switching over from the illustrated initial setting in which the output voltage u of the converter, which is present at the secondary winding of the voltage transformer 3/ü 1 independently of the setting of the polarity reversing switch 3/K2, is short-circuited through a resistor designated by 3/R.Due to the now reversed changeover switch 3/Ki, on the one hand the voltage present at the secondary winding of the transformer 3/ü 1 is fed through the line 103 to the secondary winding of the current transformer U2 and then the line 110 to an input of the power direction recognition means 2/1 of the control unit 2, and on the other hand the positive input of the amplifier 2/2 of the unit 2 is connected through the output 104 of the control unit 3 with ground potential 0 and the amplifier 2/2 is activated thereby.This has the consequence that the output 105 of the regulator 2/3 so influences the control unit 1 that the output voltage u of the converter WR is set to be higher than the nominal value thereof, which is registered by means of the voltage monitor SpW and acknowledged as a report signal of the control unit 1 through the line 106 and the corresponding input of the control unit 3 to the storage member 3/3. As a result, this delivers an actuating signal for resetting of the polarity reversing switch 3/K2.

Through the now changed-over polarity reversing switch, the polarity-reversed converter output voltage u present at the secondary winding of the voltage transformer 3/ü 1 is fed through the output 103 and the recognition means 2/1 of the control unit 2 to the amplifier 2/2 so that the output 105 of the regulator 2/3 this time so influences the control unit 1 that the output voltage u of the converter WR is set lower than the nominal value thereof. This is in turn recorded by means of the voltage monitor SpW of the control unit 1 and acknowledged as report signal by way of the line 107 and the corresponding input of the control unit 3 to the storage member 3/4.As a consequence of this storage, the running time of the timing member 3/2 is interrupted by way of the Q-input of the storage member 3/4, whereby the actuating signal for the resetting of the change-over switch 3/K1 is then taken away from this and the switch goes back into the initial setting. With this, the effective connection between the control unit 3 and the control unit 2 and furthermore the blocking of the previously opened parallel switching contactor K3 is cancelled by way of the control unit 1 in consequence of the removal of the output signal of the timing member 3/2 at the output 1 08'.

After the contactor K3 is closed and thereby the output voltage u of the converter WR connected with the load rail S, the storage member 3/3 and, in dependence thereon, the storage member 3/4 are set back into the initial state through a signal from the contactor K3 by way of the input 109.

With the contactor K3 and the switch 3/K1 closed in initial setting, the power regulating loop is closed for the parallel operation, for which purpose the voltage Uses formed at the control collecting rail SS is fed by way of 104 into the unit 2 as a target value for the power regulation.

The afore-described testing operations are evident in Fig. 2A with the aid of timing diagrams which reproduce the temporal course of the signals at the inputs and outputs of the control unit 3 starting with the delivery of the signal of the control unit 1 to the input 101 of the unit 3 at the instant t101.

The running time, starting at t101, of the timing member 3/1 is terminated at the instant t311. At the instant t102, the timing member 3/2 is set into motion by the signal delivered from the control unit 1 to the input 102. During the time duration T3lKl, the switch 3/K1 is changed over, the differential amplifier 2/2 is activated and a signal exists at the output 108', which is delivered to the control unit 1. The first return report signal arrives at the input 106, whereby the storage member 3/3 is set; thereafter, the second return report signal of the control unit 1 arrives at the input 107' at the instant t,07, whereby the storage member 3/4 is. set and the running time of the timing member 3/2 breaks off. As a result, the signal at the output 108' is terminated. The contactor K3 is freed and the storage member 3/3 and, in dependence thereon, the storage member 3/4 are reset through a signal delivered on the closing of the contactor K3 at the instant tK3.

In case either or both return report signals of the control unit 1 through the inputs 106 and 107, respectively, to the storage member 3/3 and 3/4, respectively, are absent during the automatic performance of the testing functions of the control unit 3 as a consequence of a disturbance ascertained through this testing, then the unreadiness of the power control loop of the converter WR for the parallel operation at the collecting rail S is indicated thereby. Then, after the end of the running time of the timing member 3/1, an AND-condition is given at both the inputs of the AND-member 3/5 arranged downstream of the timing members 3/1 and 3/2 so that the switching-off of the converter is affected by means of an output signal from this AND-member by way of the output 108 to the control unit 1.

The testing operations in the case of a disturbance causing the absence of the second return report signal are evident in Fig. 2B with the aid of timing diagrams which correspond to those of Fig. 2A. In consequence of the absence of the second return report signal (compare the timing diagram 107), the running time of the timing member 3/2 is not broken off so that it continues up to the end (instant t312). The time duration T3lKl and the signal, which exists during this duration and is delivered at the output 108', are thereby terminated. The running time of the timing member 3/1 is terminated at the instant t311. Due to the fact that its running time is terminated and that the running time of the timing member 3/2 still persists, an AND-condition results at both inputs of the AND-member 3/5, so that a signal is delivered at its output 108 to the control unit 1, which signal switches off the converter. The signals delivered by the control unit 1 to the inputs 101 and 102 of the control unit 3 are also terminated as a result. At the instant t3/2, the predetermined running time of the timing member 3/2 is terminated and thereby also the switch-off signal 108 resulting from the ANDcondition at the inputs of the AND-member 3/5.

No signal from the contactor K3 arrives at the input 109 of the control unit 3, since the converter has previously been switched off by the AND-condition signal 108.

Claims (4)

1. Control means for a power converter connectible at output means thereof by way of switching means to a load collecting rail to operate in parallel with at least one further such converter connected to the rail, the control means comprising a first control unit to control and monitor operation of the converter, a second control unit to regulate the power of the converter by way of the first control unit, and a third control unit so connected at input means thereof to the first control unit and the switching means and at output means thereof to the first and second control units as to be operable, in response to application of voltage to the converter and after testing of the control, monitoring and regulating functions of the first and second control units has been performed, to test in a predetermined sequence of steps the operational readiness of the converter for connection to the rail.

2. Control means as claimed in claim 1, wherein the second control unit is connected at input means thereof to output means of a first and a second transformer which are serially connected by primary windings thereof between the converter output means and the switching means to sense the values respectively of the output current and the output voltage of the converter, the first control unit is arranged to set the value of the output voltage of the converter in dependence on a regulating signal from the second control unit and to control connection of the converter to the rail by way of the switching means and comprises a voltage monitor connected to the output means of the second transformer to monitor the value of the converter output voltage and to provide a first and a second output signal when such value is respectively above and below a nominal value, and the third control unit comprises a third transformer connected at input means thereof to the converter output means, a change-over switch settable to cause and resettable to terminate application of drive signals to the second control unit, one of the drive signals being provided by the output voltage of the third transformer fed through a secondary winding of the first transformer and the second control unit being so operable in response to the application thereto of such drive signals as to deliver a regulating signal to initially cause the converter output voltage to be set to a value above the nominal value, a polarity reversing switch operable to reverse the polarity of the output voltage of the third transformer thereby to so influence the regulating signal as to cause the converter output voltage to be reset to a value below the nominal value, first timing means actuable by a signal supplied by the first control unit to provide a first timing signal, second timing means so actuable by a further signal supplied by the first control unit and indicative of determined operational readiness of the first and second control units as to provide a second timing signal to cause the change-over switch to be set and the first control unit to control the switching means for interruption of the connection of the converter to the rail, a first trigger device actuable by the first output signal of the voltage monitor to effect said operation of the polarity reversing switch, a second trigger device actuable by the second output signal of the voltage monitor to control the second timing means to terminate the second timing signal thereby to cause the changeover switch to be reset and the first control unit to control the switching means for connection of the converter to the rail, and an AND-gate to interlink the first and second timing signals in the absence of either or both of the first and second output signals of the voltage monitor so as to provide a signal to cause the first control unit to control the switching means for interruption of the connection of the converter to the rail.

3. Control means substantially as hereinbefore described with reference to the accompanying drawings.

4. A power supply system comprising a plurality of power converters each connectible at its output by way of respective switching means to a common load collecting rail to operate in parallel with the or each other converter connected to the rail, and respective control means as claimed in any one of the preceding claims operatively connected to each of the converters.