GENERATION OF MOTOR VOLTAGE FOR A SWITCH DRIVE

Description

[0001] The invention relates to a method and a power converter for generating a motor voltage for an electric motor of a switch drive of an electric switch.

[0002] Electrical switches, such as circuit breakers or disconnect switches, typically have at least one movable switching element for interrupting and closing a current path. Moving this switching element requires mechanical energy, which is often provided by an electric motor, as described, for example, in US 2019 / 237274 A1. This motor drives the switching element directly or via a gearbox, or it charges an energy storage device. A spring accumulator with a spring that can be tensioned by the electric motor is used as an energy storage device. Due to regulatory requirements and customer specifications, the electrical supply voltages available to electric motors vary considerably, differing not only in voltage level but also in voltage waveform (direct current, single-phase or multi-phase alternating current).To operate an electric motor at different supply voltages, a power converter is used, for example, to generate a motor voltage for the electric motor from the respective supply voltage. Such a power converter first converts a supply voltage into a DC link voltage and then generates the motor voltage by pulse-width modulation of the DC link voltage.

[0003] Document US 9,450,492 B1 discloses a method for comparing the time-dependent change of the input voltage in a switched-mode power supply with predefined threshold values. If the difference exceeds the threshold values, a storage element updates its stored value with the latest value of the supply voltage input. An accumulator is updated with a non-zero value when the difference measurement exceeds the threshold values, thereby applying a correction factor to an integrator in the PWM controller's control loop for a limited time.

[0004] The invention is based on the objective of providing an improved method and an improved power converter for generating a motor voltage for an electric motor of a switch drive of an electric switch, in order to be able to generate the motor voltage flexibly from different and changing supply voltages.

[0005] The problem is solved according to the invention by a method with the features of claim 1, a power converter with the features of claim 9, an electrical switch with the features of claim 13 and a computer program with the features of claim 15.

[0006] Advantageous embodiments of the invention are the subject of the dependent claims.

[0007] In the inventive method for generating a motor voltage for an electric motor of a switch drive of an electrical switch, a DC link voltage is generated from a supply voltage, and the motor voltage is generated by pulse width modulation of the DC link voltage. A tolerance range for changes in the DC link voltage is defined, and the actual value of the DC link voltage is continuously measured. After the first measurement, the actual value is stored in a voltage variable. After each subsequent measurement, it is checked whether a deviation of the actual value from the value stored in the voltage variable is within the tolerance range. The actual value is stored in the voltage variable if the deviation is outside the tolerance range.After each storage of an actual value in the voltage variable, a duty cycle for the pulse width modulation is calculated that depends on this actual value, and the pulse width modulation is performed with this duty cycle.

[0008] In the method according to the invention, the motor voltage is generated by pulse-width modulation of a DC link voltage derived from a supply voltage. The duty cycle of the pulse-width modulation is adapted to the respective supply voltage in order to generate the motor voltage from different and changing supply voltages. However, recalculating the duty cycle requires relatively high computing power. The invention therefore provides for recalculating the duty cycle only when there is a significant change in the DC link voltage. For this purpose, a tolerance range for changes in the DC link voltage is defined, and a voltage variable is used in which a measured value of the DC link voltage is stored.The duty cycle is only recalculated if the deviation of the current DC link voltage from the value stored in the voltage variable is outside the tolerance range. Furthermore, with each recalculation of the duty cycle, the value of the voltage variable is updated to reflect the current DC link voltage. This avoids recalculating the duty cycle for only minor changes in the supply voltage, thus saving valuable time and processing power.

[0009] The tolerance range can be defined symmetrically or asymmetrically around the value stored in the stress variable. Furthermore, the limits of the tolerance range can be defined by absolute or relative values ​​of the deviation of the actual value from the value stored in the stress variable.

[0010] In one embodiment of the invention, the number of duty cycle calculations is recorded. In other words, the (re)calculations of the duty cycle are counted. This allows for advantageous analysis of whether the tolerance range is appropriately chosen and, if necessary, the tolerance range can be adjusted. Furthermore, instabilities in the supply voltage and / or the switch drive, which lead to frequent, significant fluctuations in the DC link voltage, can be detected.

[0011] For example, a threshold for the number of calculations can be set, the number of calculations compared to the threshold, and a warning signal generated if the number of calculations reaches or exceeds the threshold. Additionally or alternatively, the number of calculations can be displayed on a display unit.

[0012] An inventive power converter for generating a motor voltage for an electric motor, a drive, or an electric switch comprises two power converter units, a measuring unit, and a control unit. A first power converter unit is configured to generate a DC link voltage from a supply voltage. The measuring unit is configured to continuously measure the actual value of the DC link voltage. The second power converter unit is configured to generate the motor voltage by pulse-width modulation of the DC link voltage.The control unit is configured to store a predefinable tolerance range for a change in the DC link voltage, to store the actual value in a voltage variable after the first measurement of the actual value, to check after each subsequent measurement of the actual value whether a deviation of the actual value from the value stored in the voltage variable is within the tolerance range, and to store the actual value in the voltage variable if the deviation of the actual value from the value stored in the voltage variable is outside the tolerance range, and after each storage of an actual value in the voltage variable to calculate a duty cycle of the pulse width modulation dependent on this actual value and to control the pulse width modulation with this duty cycle.

[0013] In one embodiment of a power converter according to the invention, the control unit is configured to record the number of calculations performed on the duty cycle. Furthermore, the control unit can be configured to store a predefined threshold value for the number of calculations, compare the number of calculations with the threshold value, and generate a warning signal when the number of calculations reaches the threshold value. Alternatively or additionally, the power converter can have a display unit configured to show the number of calculations.

[0014] A power converter according to the invention enables the implementation of the method according to the invention. The advantages of such a power converter therefore correspond to the advantages of the method according to the invention mentioned above.

[0015] An electrical switch according to the invention comprises a switch drive with an electric motor and a power converter according to the invention for generating a motor voltage for the electric motor. In particular, the electrical switch can be a circuit breaker or a disconnect switch.

[0016] A computer program according to the invention comprises instructions which, when the computer program is executed by a control unit, cause the control unit to execute the method according to the invention.

[0017] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings. These drawings show: FIG 1 a block diagram of an electrical switch, FIG 2 a circuit diagram of a power converter, FIG 3 a flowchart of a method for generating a motor voltage.

[0018] Corresponding parts are marked with the same reference symbols in the figures.

[0019] Figure 1 (FIG 1 Figure 1 shows a block diagram of an embodiment of an electrical switch 1 according to the invention, for example, a circuit breaker or a disconnect switch. The switch 1 comprises a power converter 3 according to the invention, a switch actuator 5 with an electric motor 7 and an energy storage device 9, and a switching element 11. The power converter 3 is configured as shown below with reference to Figure 3 (FIG 3The switch 1 generates a motor voltage for the electric motor 7 from a supply voltage, as described in more detail below. The energy storage device 9 can be charged by the electric motor 7. For example, the energy storage device 9 is a spring-loaded device with a spring that can be tensioned by the electric motor 7. The energy stored in the energy storage device 9 enables the switching element 11 to be moved. By moving the switching element 11, a current path can be interrupted and closed. Alternative embodiments of the switch 1 provide, for example, that instead of an energy storage device 9, the switching element 11 can be driven directly by the electric motor 7 or via a gearbox.

[0020] Figure 2 (FIG 2Figure 1 shows an embodiment of a power converter 3 according to the invention. The power converter 3 comprises two power converter units 13, 15, a DC link 17, a measuring unit 19, and a control unit 21. Each power converter unit 13, 15 has two switching units 23, 24 connected in series, between which a power converter terminal 25, 26 is arranged. The switching units 23, 24 are, for example, controllable semiconductor switches such as IGBTs or MOSFETs. Alternatively, the switching units 23 of the first power converter unit 13 are diodes and the switching units 24 of the second power converter unit 15 are controllable semiconductor switches such as IGBTs or MOSFETs. The DC link 17 comprises two DC link lines 27, 28, which connect the two power converter units 13, 15 to each other, and a DC link capacitor 29, the electrodes of which are each connected to one of the DC link lines 27, 28.The measuring unit 19 is set up to measure a DC link voltage between the DC link lines 27 and 28. The controllable switching units 23 and 24 can be controlled by the control unit 21.

[0021] During operation of the power converter 3, a supply voltage is applied between the power converter terminal 25 of a first power converter unit 13 and one of the DC link lines 27, 28. The first power converter unit 13 generates the DC link voltage from the supply voltage. The supply voltage can be a single-phase AC voltage or a DC voltage. If the supply voltage is a single-phase AC voltage, it is rectified by the first power converter unit 13 to produce the DC link voltage. If the supply voltage is a DC voltage, it is used directly as the DC link voltage, for example, with one switching unit 23 of the first power converter unit 13 permanently open and the other switching unit 23 of the first power converter unit 13 permanently closed.The second converter unit 15 generates the motor voltage for the electric motor 7 by pulse width modulation of the DC link voltage, as described in more detail below. For this purpose, a motor winding of the electric motor 7 is connected to the converter terminal 26 of the second converter unit 15.

[0022] The in FIG 2The illustrated embodiment of a power converter 3 is configured to generate a single-phase motor voltage. Other embodiments may provide that the power converter 3 can generate a multi-phase motor voltage, wherein the second power converter unit 15 has a pair of switching units 24 and an intermediate power converter terminal 26 for each phase of the motor voltage. Additionally or alternatively, other embodiments may provide that the first power converter unit 13 has a pair of switching units 23 and an intermediate power converter terminal 25 for each phase of a multi-phase supply voltage in order to generate the DC link voltage from a multi-phase supply voltage.

[0023] Figure 3 (FIG 3 Figure 100 shows a flowchart of an embodiment of a method according to the invention for generating a predetermined motor voltage with a [missing information] FIG 1The power converter 1 shown. The method is implemented by a computer program executed by the control unit 21, which evaluates actual values ​​of the DC link voltage measured by the measuring unit 19.

[0024] In the first process step 101, a tolerance range for a change in the DC link voltage is specified. The tolerance range is defined symmetrically or asymmetrically around a value that is stored in a voltage variable during the process. The limits of the tolerance range are defined by absolute or relative values ​​of the deviation of the actual value from the value stored in the voltage variable.

[0025] In a second process step 102, the power converter 3 is activated and an actual value of the DC link voltage is measured for the first time.

[0026] In a third process step 103, the current actual value of the DC link voltage is stored in the voltage variable.

[0027] In a fourth process step 104, a duty cycle of the pulse width modulation, dependent on the value stored in the voltage variable, is calculated in order to generate the motor voltage by pulse width modulation of the DC link voltage.

[0028] In a fifth process step 105, the DC link voltage is pulse-width modulated with the duty cycle calculated in the fourth process step 104, whereby the switching units 24 of the second converter unit 15 are controlled accordingly by the control unit 21.

[0029] In a sixth process step 106, a current actual value of the DC link voltage is measured.

[0030] In a seventh process step 107, it is checked whether the deviation of the actual value measured in the sixth process step 106 from the value stored in the voltage variable lies within the tolerance range specified in the first process step 101. If this is the case, the process continues with an eighth process step 108. Otherwise, the process continues with the third process step 103.

[0031] In the eighth process step 108, it is checked whether the energy storage device 9 is fully charged. If this is the case (that is, if the energy storage device 9 is fully charged), the process continues with a ninth process step 109. Otherwise, the process continues with the fifth process step 105.

[0032] In the ninth process step 109, the electric motor 7 is switched off and the process is terminated.

[0033] Optionally, the procedure can include counting the duty cycle calculations. Furthermore, it can include displaying the number of calculations and / or generating a warning signal when the number of calculations reaches or exceeds a predefined threshold. For example, in the second procedure step 102, a counter variable for the number of calculations is initialized with the value zero. Additionally, in the first procedure step 101, a threshold value for the number of calculations can be specified. In the fourth procedure step 104, the value stored in the counter variable is then incremented by one. The value currently stored in the counter variable is displayed, for example, on a display unit 22 of the power converter 3.If a threshold value for the number of calculations was specified in the first procedure step 101, in the fourth procedure step 104, after incrementing the value stored in the counter variable, this value can be compared with the threshold value and an optical and / or acoustic warning signal can be issued if the value stored in the counter variable matches or exceeds the number of calculations.

[0034] If the switch 1 does not have an energy storage device 9, but the switching element 11 can be driven directly or via a gearbox by the electric motor 7, the eighth process step 108 checks whether the switching element 11 has reached a switching position into which it can be moved by the electric motor 7. If this is the case (that is, if the switching element 11 has reached the switching position), the process continues with a ninth process step 109. Otherwise, the process continues with the fifth process step 105. The other process steps 101 to 107 and 109 are carried out as described above.

[0035] Although the invention has been further illustrated and described by means of preferred embodiments, the invention is not limited by the disclosed examples. The scope of protection of the invention is defined by the appended claims.

Claims

1. Method for producing a motor voltage for an electric motor (7) of a switch drive (5) of an electrical switch (1), wherein - a supply voltage is used to produce an intermediate-circuit DC voltage and - the motor voltage is produced by way of a pulse-width modulation of the intermediate-circuit DC voltage, characterized in that - a tolerance range for a change in the intermediate-circuit DC voltage is predefined, - an actual value of the intermediate-circuit DC voltage is continuously measured, - the first measurement of the actual value is followed by storage of the actual value in a voltage variable, - every further measurement of the actual value is followed by testing of whether a difference between the actual value and the value stored in the voltage variable is within the tolerance range, and storage of the actual value in the voltage variable if the difference between the actual value and the value stored in the voltage variable is outside the tolerance range, - and every storage of an actual value in the voltage variable is followed by calculation of a duty cycle of the pulse width modulation that is dependent on this actual value and performance of the pulse width modulation using this duty cycle.

2. Method according to Claim 1, wherein the tolerance range is predefined symmetrically about the value stored in the voltage variable.

3. Method according to Claim 1, wherein the tolerance range is predefined asymmetrically about the value stored in the voltage variable.

4. Method according to one of the preceding claims, wherein the limits of the tolerance range are predefined by absolute values of the difference between the actual value and the value stored in the voltage variable.

5. Method according to one of Claims 1 to 4, wherein the limits of the tolerance range are predefined by relative values of the difference between the actual value and the value stored in the voltage variable.

6. Method according to one of the preceding claims, wherein a number of calculations is recorded for calculations of the duty cycle.

7. Method according to Claim 6, wherein a threshold value for the number of calculations is predefined, the number of calculations is compared with the threshold value, and a warning signal is generated if the number of calculations reaches or exceeds the threshold value.

8. Method according to Claim 6 or 7, wherein the number of calculations is displayed on a display unit (22).

9. Converter (3) for producing a motor voltage for an electric motor (7) of a drive of an electrical switch (1), the converter (3) comprising - a first converter unit (13), configured to produce an intermediate-circuit DC voltage from a supply voltage, - a measuring unit (19), configured to continuously measure an actual value of the intermediate-circuit DC voltage, - a second converter unit (15), configured to produce the motor voltage by way of a pulse width modulation of the intermediate-circuit DC voltage, and - a control unit (21), characterized in that the control unit is configured • to store a predefinable tolerance range for a change in the intermediate-circuit DC voltage, • to store the actual value in a voltage variable after the first measurement of the actual value, • to test, after every further measurement of the actual value, whether a difference between the actual value and the value stored in the voltage variable is within the tolerance range, and to store the actual value in the voltage variable if the difference between the actual value and the value stored in the voltage variable is outside the tolerance range, • and to calculate, after every storage of an actual value in the voltage variable, a duty cycle of the pulse width modulation that is dependent on this actual value and to control the pulse width modulation using this duty cycle.

10. Converter (3) according to Claim 9, wherein the control unit (21) is configured to record a number of calculations for calculations of the duty cycle.

11. Converter (3) according to Claim 10, wherein the control unit (21) is configured to store a predefinable threshold value for the number of calculations, to compare the number of calculations with the threshold value and to generate a warning signal if the number of calculations reaches the threshold value.

12. Converter (3) according to Claim 9 or 10, having a display unit (22) that is configured to display the number of calculations.

13. Electrical switch (1) having a switch drive (5), which comprises an electric motor (7), and a converter (3) according to one of Claims 9 to 12 for producing a motor voltage for the electric motor (7).

14. Electrical switch (1) according to Claim 13, which is a circuit breaker or a disconnector.

15. Computer program comprising instructions that, when the computer program is executed by a control unit (21), cause said control unit to carry out the method according to one of Claims 1 to 8, using a converter (3) according to one of Claims 9 to 12.