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Title:
HVDC SYSTEM AND METHOD FOR ELECTRICAL SHOCK PREVENTION
Document Type and Number:
WIPO Patent Application WO/2018/149469
Kind Code:
A1
Abstract:
The present invention provides a HVDC system 100 and corresponding method 200 carried out by the system 100. The system 100 comprises a RPU 101 and at least one RPR 102 connected to the RPU 101 via two power lines 103. The RPU 101 comprises: a control circuit 104 configured to control at least a first RPU switch K3, wherein a HVDC voltage is supplied by the RPU 101 across the two power lines 103, if the first RPU switch K3 is turned ON, and a first determining unit 105 configured to determine a current I1/I2 flowing on a first power line 103a/103b of the two power lines 103. The RPR 102 includes: a control circuit 106 configured to periodically turn ON and OFF a first RPR switch Q1 with an on-time and an off-time in each of predetermined time periods, wherein no current flows through the RPR 102 on the two power lines 103, if the first RPR switch K3 is turned OFF. The control circuit 104 of the RPU 101 is configured to turn OFF the first RPU switch K3, if the current I1/I2 flowing on the first power line 103a/103b is below or equal to a first threshold value during a complete predetermined time period, or the current I1/I2 flowing on the first power line 103a/103b is above a second threshold value during a complete predetermined time period.

Inventors:
ZHANG, Guoqing (Munich, 80992, DE)
STIEDL, Andreas (Munich, 80992, DE)
XIAO, Zhiming (Munich, 80992, DE)
TABAKOV, Michael (Munich, 80992, DE)
Application Number:
EP2017/053197
Publication Date:
August 23, 2018
Filing Date:
February 14, 2017
Export Citation:
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Assignee:
HUAWEI TECHNOLOGIES CO., LTD. (Huawei Administration Building Bantian Longgang District, Shenzhen, Guangdong 9, 518129, CN)
ZHANG, Guoqing (Munich, 80992, DE)
International Classes:
H02H3/14; G01R31/02; H02H3/17; H02H5/10; H02H5/12; H02H11/00
Foreign References:
FR2932917A12009-12-25
EP2804163A12014-11-19
US20160202304A12016-07-14
US20150381108A12015-12-31
Other References:
None
Attorney, Agent or Firm:
KREUZ, Georg (Huawei Technologies Duesseldorf GmbH Riesstr. 8, Munich, 80992, DE)
Download PDF:
Claims:
CLAIMS

1. Higher Voltage Direct Current, HVDC, system (100) comprising a Remote Power Unit, RPU, (101) and at least one Remote Power Receiver, RPR, (102) each one connected to the RPU via two power lines (103),

wherein the RPU (101) comprises:

a control circuit (104) configured to control at least a first RPU switch (K3), wherein a HVDC voltage is supplied by the RPU (101) across the two power lines (103), when the first RPU switch (K3) is turned ON, and

a first determining unit (105) configured to determine a current (Ii, I2) flowing on a first power line (103a, 103b) of the two power lines (103);

wherein the RPR (102) includes:

a control circuit (106) configured to periodically turn ON and OFF a first RPR switch (Ql) with an on-time (TON) and an off-time (TOFF) in each of predetermined time periods, wherein no current flows through the RPR (102) on the two power lines (103), when the first RPR switch (Ql) is turned OFF;

wherein the control circuit (104) of the RPU (101) is configured to turn OFF the first RPU switch (K3), when

the current (Ii, I2) flowing on the first power line (103a, 103b) is below or equal to a first threshold value during a complete predetermined time period, or

the current (Ii, I2) flowing on the first power line (103a, 103b) is above a second threshold value during a complete predetermined time period.

2. HVDC system (100) according to claim 1, wherein

the RPU (101) further comprises a second determining unit (1000) configured to determine a current (Ii, I2) flowing on a second power line (103b, 103a) of the two power lines (103), and

the control circuit (104) of the RPU is configured to turn OFF the first RPU switch (K3), when

the current (Ii, I2) flowing on the first power line (103a, 103b) is below or equal to the first threshold value during a complete predetermined time period, or

the current (Ii) flowing on the first power line (103a, 103b) and/or the current (I2) flowing on the second power line (103b, 103a) is above the second threshold value during a complete predetermined time period.

3. HVDC system (100) according to claim 1 or 2, wherein

the first determining unit (105) is a first current measuring unit configured to directly measure the current (Ii, I2) flowing on the first power line (103a, 103b).

4. HVDC system (100) according to one of the claims 1 to 3, wherein

the second determining unit (1000) is a second current measuring unit configured to directly measure the current (Ii, I2) flowing on the second power line (103b, 103a). 5. HVDC system (100) according to claim 3 or 4, wherein

the first threshold value is between 2-20mA, preferably between 5- 15mA, more preferably 10mA, and/or

the second threshold value is between 20-50mA, preferably between 25 -35mA, more preferably 30mA.

6. HVDC system (100) according to claim 1 or 2, wherein

the first determining unit (105) is a first voltage measuring unit configured to measure a voltage (VDI) provided by a first diode (Di), the first diode (Di) being configured to provide a first voltage value, when the current (Ii, I2) flowing on the first power line (103a, 103b) is equal to the first threshold value, and is configured to provide a second voltage value, when the current (Ii, I2) flowing on the first power line (103a, 103b) is above the second threshold value.

7. HVDC system (100) according to one of claims 1, 2 or 6 wherein

the second determining unit (1000) is a second voltage measuring unit configured to measure a voltage (VD2) provided by a second diode (D2), the second diode (D2) being configured to provide a first voltage value, when the current (Ii , I2) flowing on the second power line (103b, 103a) is equal to the first threshold value, and is configured to provide a second voltage value, when the current (Ii, I2) flowing on the second power line (103b, 103a) is above the second threshold value.

8. HVDC system (100) according to claim 6 or 7, wherein

the first threshold value is equal to the second threshold value, and is preferably 0mA.

9. HVDC system (100) according to one of claims 6 to 8, wherein the first threshold value is between 0-5mA, preferably is 0mA, and/or

the second threshold value is between 0-5mA, preferably is 0mA, and

the first voltage value is between 0-0.2V, preferably is 0V, and/or

the second voltage value is between 0.6-0.8V, preferably is 0.7V.

10. HVDC system (100) according to one of the claims 1 to 9, wherein

the control circuit (104) of the RPU (101) is further configured to control a second RPU switch (K2), wherein a DC voltage below 60V, preferably of 12V, is supplied across the two power lines (103), when the second RPU switch (K2) is turned ON,

wherein the control circuit (104) of the RPU (101) is configured to turn ON the first RPU switch (K3) only, when the current (Ii, I2) flowing on the first power line (103a, 103b) is above a third threshold value for a predetermined amount of time, after the second RPU switch (K2) is turned ON.

11. HVDC system (100) according to claim 10, wherein

the control circuit (104) of the RPU (101) is configured to turn ON the first RPU switch (K3) only, when the second RPU switch (K2) is turned OFF.

12. HVDC system (100) according to claim 10 or 11, wherein

the control circuit (106) of the RPR (102) is further configured to control a second RPR switch (K4), wherein a resistance (Rl) is connected in parallel to the two power lines (103) in the RPR (102), when the second RPR switch (K4) is turned ON,

the second RPR switch (K4) is default ON, and

the control circuit (106) of the RPR (102) is configured to turn OFF the second RPR switch (K4), after the control circuit (106) of the RPR (102) is powered for a predetermined amount of time.

13. HVDC system (100) according to one of the claims 1 to 12, wherein

the RPU (101) further includes a third RPU switch (Kl) configured to be manual controlled or auto controlled by another manual switch,

wherein the control circuit (104) of the RPU (101) is configured to turn ON the second RPU switch (K2) only, when the third RPU switch (Kl) is turned ON.

14. HVDC system (100) according to one of the claims 1 to 13, wherein the on-time (TON) is between 50-400ms, preferably between 100-200ms, more preferable 150msand

the off-time (TOFF) is between 5- 15ms, preferably 10ms. 15. Method (200) for operating a Higher Voltage Direct Current, HVDC, system (100) comprising a Remote Power Unit, RPU, (101) and at least one Remote Power Receiver, RPR, (102) connected to the RPU (101) via two power lines (103),

wherein the method (3200) comprises the steps of:

controlling (201) at least a first RPU switch (K3), wherein a HVDC voltage is supplied by the RPU (101) across the two power lines (103), when the first RPU switch (K3) is turned ON,

determining (202) a current (Ii, I2) flowing on a first power line (103a, 103b) of the two power lines (103);

periodically turning ON and OFF (203) a first RPR switch (Ql) with an on-time (TON) and an off-time (TOFF) in each of predetermined time periods, wherein no current flows through the RPR (102) on the two power lines (103), when the first RPR switch (Ql) is turned OFF, and

turning OFF (204) the first switch (K3), when

the current (Ii, I2) flowing on the first power line (103a, 103b) is below or equal to a first threshold value during a complete predetermined time period, or

the current (Ii, I2) flowing on the first power line (103a, 103b) is above a second threshold value during a complete predetermined time period.

16. A Remote Power Unit, RPU, (101) for a Higher Voltage Direct Current, HVDC, system (100), wherein the RPU (101) is connected to at least one Remote Power Receiver, RPR, (102) via two power lines (103),

wherein the RPU (101) comprises:

a control circuit (104) configured to control at least a first RPU switch (K3), wherein a HVDC voltage is supplied by the RPU (101) across the two power lines (103), when the first RPU switch (K3) is turned ON, and

a first determining unit (105) configured to determine a current (Ii, I2) flowing on a first power line (103a, 103b) of the two power lines (103);

wherein the control circuit (104) of the RPU (101) is configured to turn OFF the first RPU switch (K3), when the current (Ii, I2) flowing on the first power line (103a, 103b) is below or equal to a first threshold value during a complete predetermined time period, or

the current (Ii, I2) flowing on the first power line (103a, 103b) is above a second threshold value during a complete predetermined time period.

17. A Remote Power Receiver, RPR, (102) for a Higher Voltage Direct Current, HVDC, system (100) wherein the RPR (102) is connected to a Remote Power Unit, RPU, (101) via two power lines (103) and a HVDC voltage is supplied form the RPU (101) to the RPR (102) via the two power lines (103) ,

wherein the RPR (102) includes:

a control circuit (106) configured to periodically turn ON and OFF a first RPR switch (Ql) with an on-time (TON) and an off-time (TOFF) in each of predetermined time periods, wherein no current flows through the RPR (102) on the two power lines (103), when the first RPR switch (Ql) is turned OFF.

Description:
HVDC SYSTEM AND METHOD FOR ELECTRICAL SHOCK PREVENTION

TECHNICAL FIELD The present invention relates to a Higher Voltage Direct Current (HVDC) system and a method for operating such a system. The HVDC system and method operate a Remote Power Unit (RPU) and at least one Remote Power Receiver (RPR) connected to the RPU by power supply lines, particularly, in order to prevent electrical shocks in case of system failures.

BACKGROUND

HVDC is gaining more and more importance in ICT industry. HVDC specifically means that a higher DC voltage is used, especially a voltage higher than -48Vdc, which is used in traditional ICT equipment. The HVDC voltage is, for example, defined in ITU L.1200, and the applied voltage range there is 192Vdc - 410Vdc. In a conventional HVDC (remote powering) system, a RPU supplies HVDC power to at least one distant RPR over at least two power lines. In such a HVDC system, different types of failures may lead to different conditions posing a high electrical shock risk.

For instance, as shown in Fig. 33, a line open circuit condition can occur, for example, when a cable (particularly one of the power lines of the RPU) is broken, and a load (e.g. RPR) is disconnected. This line open circuit condition should be automatically detected and signalled by some kind of alarm, since human contact with the open line is potentially harmful. In the following, the detection of such a condition is referred to as Open circuit detection'.

As shown further in Fig. 34, safety provisions (detection and alarm) should also be taken to avoid risk of electrical shock for a person coming in contact with simultaneously exposed conductive parts (particularly the power lines) between the RPU and the RPR. In the following, the detection of such a condition is referred to as 'touch both poles detection'.

Moreover, another condition that requires safety provisions is referred to in the following as 'residual current detection'. As shown in Fig. 35, in case of a certain first fault (here a short circuit occurred between the HDVC voltage and the enclosure of the RPU, i.e. effectively Ri=0), an automatic disconnection of the power supply of the RPU should at least be implemented. In particular, such a disconnection is crucial in the case of an additional second fault, as shown in Fig 36. Here, additionally the power lines supplying the RPR are accidently contacted to the enclosure of the RPR, which leads to a high electrical shock risk for any person touching the enclosure of the RPR.

But also, as shown in Fig. 37, if only the above-mentioned first fault occurs, a very dangerous condition is created for a person contacting (here referred to as a second fault) one of the power lines between the RPU and the RPR. Also, as shown in Fig. 38, a first fault may occur downstream of the output interface of the RPU, wherein the insulation between a "+"pole or a "-"pole with earth is decreased to a low value. An automatic disconnection of the power supply of the RPU should be implemented in the case of an additional second fault, like human contact with the power lines.

Accordingly, Open circuit detection', 'touch both poles detection', and 'residual current detection' can help greatly to prevent electrical shocks in FJVDC systems. In addition, the RPU should also have an automatic recovery procedure from a safe mode to a normal operation mode, which is referred to in the following as 'safe start up'.

Conventional HVDC systems at best operate with a safety algorithm that compares a flowing current value with a reference current value. Thereby, the algorithm particularly checks, whether or not a sample current value is always more than or equal to the reference current value in one time period. If this is the case, the RPU turns off its output.

This conventionally used safety algorithm has, however, some severe flaws. In particular, the algorithm is only usable for the above-described 'touch both poles detection'. It cannot be used for 'safe start up', 'open circuit detection', or 'residual current detection'. Furthermore, the conventional algorithm measures the flowing current directly, which is not the best approach for each kind of situation.

SUMMARY

In view of the above-mentioned problems and disadvantages, the present invention aims to improve conventional HVDC systems and their safety algorithms. The present invention has particularly the object to provide a HVDC system and method, with which electrical shocks can be prevented more effectively. In particular, the HVDC system and method should be usable for 'safe start up', Open circuit detection', 'touch both poles detection', and 'residual current detection'. Moreover, a more flexible use for different situations is desired. The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims.

A first aspect of the present invention provides a HVDC system comprising a RPU and at least one RPR connected to the RPU via two power lines, wherein the RPU comprises: a control circuit configured to control at least a first RPU switch, wherein a HVDC voltage is supplied by the RPU across the two power lines, if the first RPU switch is turned ON, and a first determining unit configured to determine a current flowing on a first power line of the two power lines; wherein the RPR includes: a control circuit configured to periodically turn ON and OFF a first RPR switch with an on-time and an off-time in each of predetermined time periods, wherein no current flows through the RPR on the two power lines, if the first RPR switch is turned OFF; wherein the control circuit of the RPU is configured to turn OFF the first RPU switch, if the current flowing on the first power line is below or equal to a first threshold value during a complete predetermined time period, or the current flowing on the first power line is above a second threshold value during a complete predetermined time period. By determining the flowing current on one power line in this way, and by detecting specific current conditions with respect to a predetermined time period, which is defined by the sum of on-time and an off-time, at least 'touch both poles detection' and 'open circuit detection' are enabled in a very precise and fast manner. This is firstly due to the fact, that during the on-time a relatively large current should normally flow, and the drop to zero current flow can be detected rather precisely. Secondly, that during an off-time normally no current should flow, and the rise to a comparatively still small current above the threshold value can be detected rather precisely. The system can further be well extended to enable 'residual current detection', and is also suitable for 'safe start up'. In addition, the system may be operated both in a 'current method', in which the current is determined directly, and in a 'voltage method', in which the current is determined indirectly.

In a first implementation form of the system according to the first aspect, the RPU further comprises a second determining unit configured to determine a current flowing on a second power line of the two power lines, and the control circuit of the RPU is configured to turn OFF the first RPU switch, if the current flowing on the first power line is below or equal to the first threshold value during a complete predetermined time period, or the current flowing on the first power line and/or the current flowing on the second power line is above the second threshold value during a complete predetermined time period.

Determining in this way also the current flowing on the other power line, and additionally detecting the specific current condition above, allows a fast and precise 'residual current detection'.

In a second implementation form of the system according to the first aspect as such or according to the first implementation form of the first aspect, the first determining unit is a first current measuring unit configured to directly measure the current flowing on the first power line.

In a third implementation form of the system according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the second determining unit is a second current measuring unit configured to directly measure the current flowing on the second power line.

With these current measuring units, the system can be operated in a 'current method', which is advantageous in some cases.

In a fourth implementation form of the system according to the second or third implementation form of the first aspect, the first threshold value is between 2-20mA, preferably between 5- 15mA, more preferably 10mA, and/or the second threshold value is between 20-50mA, preferably between 25-35mA, more preferably 30mA.

The above-described threshold values lead to a particularly precise detection of the different current conditions, and thus improve the electrical shock prevention.

In a fifth implementation form of the system according to the first aspect as such or according to the first implementation form of the first aspect, the first determining unit is a first voltage measuring unit configured to measure a voltage provided by a first diode, the first diode being configured to provide a first voltage value, if the current flowing on the first power line is equal to the first threshold value, and is configured to provide a second voltage value, if the current flowing on the first power line is above the second threshold value. In a sixth implementation form of the system according to the first aspect as such or according to the first or fifth implementation form of the first aspect, the second determining unit is a second voltage measuring unit configured to measure a voltage provided by a second diode, the second diode being configured to provide a first voltage value, if the current flowing on the second power line is equal to the first threshold value, and is configured to provide a second voltage value, if the current flowing on the second power line is above the second threshold value.

With these voltage measuring units, the system can be operated in a 'voltage method', which is advantageous in some cases. In a seventh implementation form of the system according to the fifth or sixth implementation form of the first aspect, the first threshold value is equal to the second threshold value, and is preferably 0mA.

In an eighth implementation form of the system according to the fifth to seventh implementation form of the first aspect, the first threshold value is between 0-5mA, preferably is 0mA, and/or the second threshold value is between 0-5mA, preferably is 0mA, and the first voltage value is between 0-0.2V, preferably is 0V, and/or the second voltage value is between 0.6-0.8V, preferably is 0.7V.

The above-described threshold values and voltage values lead to a particularly precise detection of the different conditions. In a ninth implementation form of the system according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the control circuit of the RPU is further configured to control a second RPU switch, wherein a DC voltage below 60V, preferably of 12V, is supplied across the two power lines, if the second RPU switch is turned ON, wherein the control circuit of the RPU is configured to turn ON the first RPU switch only, if the current flowing on the first power line is above a third threshold value for a predetermined amount of time, after the second RPU switch is turned ON.

Thus, the system is implemented with 'safe start up'.

In a tenth implementation form of the system according to the tenth implementation form of the first aspect, the control circuit of the RPU is configured to turn ON the first RPU switch only, if the second RPU switch is turned OFF. This ensures that the HVDC power is only applied after 'safe start up', thus improving the system safety.

In an eleventh implementation form of the system according to the ninth or tenth implementation forms of the first aspect, the control circuit of the RPR is further configured to control a second RPR switch, wherein a resistance is connected in parallel to the two power lines in the RPR, if the second RPR switch is turned ON, the second RPR switch is default ON, and the control circuit of the RPR is configured to turn OFF the second RPR switch, after the control circuit of the RPR is powered for a predetermined amount of time.

In this way, the current flowing on the power lines during 'safe start up' is harmless to a person. In a twelfth implementation form of the system according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the RPU further includes a third RPU switch configured to be manual controlled or auto controlled by another manual switch, wherein the control circuit of the RPU is configured to turn ON the second RPU switch only, if the third RPU switch is turned ON. The manual operation required to turn on the HVDC system is a further safety measure.

In a thirteenth implementation form of the system according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the on-time is between 50-400ms, preferably is between 100-200ms, and the off-time is between 5- 15ms, preferably is 10ms. With these values for the on-time and off-time, the detection of the various dangerous conditions is fast enough to avoid harm to any person.

A second aspect of the present invention provides a method for operating a Higher Voltage Direct Current, HVDC, system comprising a Remote Power Unit, RPU, and at least one Remote Power Receiver, RPR, connected to the RPU via two power lines, wherein the method comprises the steps of: controlling at least a first RPU switch, wherein a HVDC voltage is supplied by the RPU across the two power lines, if the first RPU switch is turned ON, determining a current flowing on a first power line of the two power lines; periodically turning ON and OFF a first RPR switch with an on-time and an off-time in each of predetermined time periods, wherein no current flows through the RPR on the two power lines, if the first RPR switch is turned OFF, and turning OFF the first switch, if the current flowing on the first power line is below or equal to a first threshold value during a complete predetermined time period, or the current flowing on the first power line is above a second threshold value during a complete predetermined time period.

In a first implementation form of the method according to the second aspect, the method further comprises determining a current flowing on a second power line of the two power lines, and turning OFF the first RPU switch, if the current flowing on the first power line is below or equal to the first threshold value during a complete predetermined time period, or the current flowing on the first power line and/or the current flowing on the second power line is above the second threshold value during a complete predetermined time period. In a second implementation form of the method according to the second aspect as such or according to the first implementation form of the second aspect, the current flowing on the first power line is determined by measuring it directly.

In a third implementation form of the method according to the second aspect as such or according to any of the previous implementation forms of the second aspect, the current flowing on the second power line is determined by measuring it directly.

In a fourth implementation form of the method according to the second or third implementation form of the second aspect, the first threshold value is between 2-20mA, preferably between 5- 15mA, more preferably 10mA, and/or the second threshold value is between 20-50mA, preferably between 25 -35mA, more preferably 30mA. In a fifth implementation form of the method according to the second aspect as such or according to the first implementation form of the second aspect, the current flowing on the first power line is determined by measuring a voltage provided by a first diode, the first diode being configured to provide a first voltage value, if the current flowing on the first power line is equal to the first threshold value, and is configured to provide a second voltage value, if the current flowing on the first power line is above the second threshold value.

In a sixth implementation form of the method according to the second aspect as such or according to the first or fifth implementation form of the second aspect, the current flowing on the second power line is determined by measuring a voltage provided by a second diode, the second diode being configured to provide a first voltage value, if the current flowing on the second power line is equal to the first threshold value, and is configured to provide a second voltage value, if the current flowing on the second power line is above the second threshold value.

In a seventh implementation form of the method according to the fifth or sixth implementation form of the second aspect, the first threshold value is equal to the second threshold value, and is preferably 0mA.

In an eighth implementation form of the method according to the fifth to seventh implementation form of the second aspect, the first threshold value is between 0-5mA, preferably is 0mA, and/or the second threshold value is between 0-5mA, preferably is 0mA, and the first voltage value is between 0-0.2V, preferably is 0V, and/or the second voltage value is between 0.6-0.8V, preferably is 0.7V.

In a ninth implementation form of the method according to the second aspect as such or according to any of the previous implementation forms of the second aspect, the method further comprises controlling a second RPU switch, wherein a DC voltage below 60V, preferably of 12V, is supplied across the two power lines, if the second RPU switch is turned ON, wherein the first RPU switch is turned ON only, if the current flowing on the first power line is above a third threshold value for a predetermined amount of time, after the second RPU switch is turned ON.

In a tenth implementation form of the method according to the tenth implementation form of the second aspect, the method further comprises turning ON the first RPU switch only, if the second RPU switch is turned OFF.

In an eleventh implementation form of the method according to the ninth or tenth implementation forms of the second aspect, the method further comprises controlling a second RPR switch, wherein a resistance is connected in parallel to the two power lines in the RPR, if the second RPR switch is turned ON, the second RPR switch is default ON, and the second RPR switch is turned OFF, after the control circuit of the RPR is powered for a predetermined amount of time.

In a twelfth implementation form of the method according to the second aspect as such or according to any of the previous implementation forms of the second aspect, the method further comprises manually controlling or auto controlling by another manual switch a third RPU switch, wherein the second RPU switch is turned ON only, if the third RPU switch is turned ON. In a thirteenth implementation form of the method according to the second aspect as such or according to any of the previous implementation forms of the second aspect, the on-time is between 50-400ms, preferably is between 100-200ms, and the off-time is between 5- 15ms, preferably is 10ms. The method of the second aspect as such and its implementations forms achieves all the advantages described for the system of the first aspect as such and its implementation forms.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

Fig. 1 shows a system according to an embodiment of the present invention.

Fig. 2 shows a method according to an embodiment of the present invention.

Fig. 3 shows a system according to an embodiment of the present invention. Fig. 4 shows a system according to an embodiment of the present invention.

Fig. 5 shows a safe start up for the system shown in Figs. 3 and 4.

Fig. 6 shows a normal working for the system shown in Figs. 3 and 4. shows open circuit detection for the system shown in Figs. 3 and 4.

shows touch both poles detection for the system shown in Figs. 3 and 4. shows a method according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a safe start up for the system shown in Figs. 10 and 11.

shows a normal working for the system shown in Figs. 10 and 11.

shows open circuit detection for the system shown in Figs. 10 and 11. shows touch both poles detection for the system shown in Figs. 10 and 11 shows residual current detection for the system shown in Figs. 10 and 11. shows a method according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a safe start up for the system shown in Figs. 18 and 19.

shows a normal working for the system shown in Figs. 18 and 19.

shows open circuit detection for the system shown in Figs. 18 and 19. shows touch both poles detection for the system shown in Figs. 17 and 18 shows a method according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a system according to an embodiment of the present invention, shows a safe start up for the system shown in Figs. 25 and 26.

shows a normal working for the system shown in Figs. 25 and 26. Fig. 29 shows open circuit detection for the system shown in Figs. 25 and 26.

Fig. 30 shows touch both poles detection for the system shown in Figs. 25 and 26.

Fig. 31 shows residual current detection for the system shown in Figs. 25 and 26.

Fig. 32 shows a method according to an embodiment of the present invention. Fig. 33 illustrates an open circuit detection condition.

Fig. 34 illustrates a touch both poles detection condition.

Fig. 35 illustrates a residual current detection condition. The first fault is upstream the output interface of the RPU.

Fig. 36 illustrates a residual current detection condition. The first fault is upstream the output interface of the RPU.

Fig. 37 illustrates a residual current detection condition. The first fault is upstream the output interface of the RPU.

Fig. 38 illustrates a residual current detection condition. The first fault is downstream the output interface of the RPU.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an HVDC system 100 according to an embodiment of the present invention. The HVDC system 100 comprises an RPU 101 and at least one RPR 102, which is connected to the RPU 101 via two power lines 103 (output). If a plurality of RPRs 102 are connected to the RPU 101, different outputs 1 ... N of the RPU 101 may be used, wherein each output provide connection to a RPR 102 by two power lines 103.

The RPU 101 comprises a first control circuit 104, which is configured to control at least a first RPU switch K3. If the RPU switch K3 is turned ON, a HVDC voltage is supplied by the RPU 101 across the two power lines 103. Accordingly, a current I1/I2 flows on one of the power lines 103 a/ 103b from the RPU to the RPR 102, and a current I 2 /11 flows on the other one of the power lines 103b/103a from the RPR 102 into the RPU 101. Exemplarily in Fig. 1, current I 2 flows from the RPU 101 to the RPR 102 on power line 103b, and current Ii flows from the RPR 102 to the RPU 101 on power line 103b.

The RPU 101 further comprises a first determining unit 105, which is configured to determine a current I1/I2 flowing on a first power line 103a/103b of the two power lines 103. In Fig. 1, exemplarily the determining unit 105 measures the current Ii on the power line 103b.

The RPR 102 includes a second control circuit 106, which is configured to control a first RPR switch Ql of the RPR 102. In particular, the control circuit 106 is configured to periodically turn ON and OFF the RPR switch Ql with an on-time TON and an off-time TOFF in each of predetermined time periods. A predetermined time period is thereby defined by one on-time and one off-time. If the first RPR switch Ql is turned OFF, no current flows through the RPR 102 on the two power lines 103.

In order to interrupt a current flow between the RPU 101 and the RPR 102, the first control circuit 104 of the RPU 101 may turn OFF the first RPU switch K3. In particular, the control circuit 104 is configured to turn the first RPU switch K3 OFF, if the current I1/I2 flowing on the first power line 103 a/ 103b is below or equal to a first threshold value during a complete predetermined time period, or if the current I1/I2 flowing on the first power line 103a/103b is above a second threshold value during a complete predetermined time period.

FIG. 2 shows a method 200 for operating an HVDC system according to an embodiment of the present invention. The HVDC system operated by the method 200 may particularly be the HVDC system 100 shown in FIG. 1. The method 200 comprises a first step 201, wherein at least a first RPU switch K3 is controlled. As shown and described with respect to FIG. 1, if the first RPU switch K3 is turned ON, an HVDC voltage is supplied by the RPU 101 across two power lines 103 connecting it to the RPR 102. In a second step 202, the method includes determining a current I1/I2 flowing on a first power line 103a/103b of the two power lines 103. The method also includes a step 203 of periodically turning ON and OFF a first RPR switch Q 1 of the RPR 102 with an on-time TON and an off-time TOFF in each of predetermined time periods. As shown in FIG. 1, no current flows through the RPR 102 on the two power lines 103, if the RPR switch Ql is turned OFF. Finally, the method 200 includes a step 204, in which the first RPU switch K3 of the RPU 101 is turned OFF. This happens, if the current I1/I2 flowing on the first power line 103 a/ 103b is below or equal to a first threshold value during a complete predetermined time period, or if the current I1/I2 flowing on the first power line 103a/103b is above a second threshold value during a complete predetermined time period. FIG. 3 shows an embodiment according to the present invention, which builds on the HVDC system 100 shown in FIG. 1. In the HVDC system 100 of FIG. 3, the determining unit 105 is specifically a current measurement unit. This unit is configured to directly measure generally the current I1/I2 flowing on a first power line 103a/103b. Here, exemplarily the current measuring unit 105 measures the current Ii flowing form RPR 102 to RPU 101 on power line 103a. Further, here the RPU switch K3 is preferably turned OFF by the control circuit 104, if the directly measured current is between the first threshold value of 2- 15mA, more preferably at 10mA.

In FIG. 3, the RPU 101 further has a second RPU switch K2 and a third RPU switch Kl . The second RPU switch K2 is also controlled by the control circuit 104. If the RPU switch K2 is turned ON, a DC voltage preferably below 60V, or as shown in FIG. 3 more preferably of 12 V, is supplied across the two power lines 103. In FIG. 3, the DC voltage of 12V is supplied by an auxiliary source 300, which is separate from a HVDC converter 301 for supplying the HVDC voltage. However, as shown in FIG. 4, the HVDC voltage and the lower DC voltage, of e.g. 12V, can both be supplied by a common converter 401. In this case, the RPU switches K2 and K3 are in this common converter 401, respectively. Otherwise, the systems 100 of FIGs 3 and 4 are similar.

The control circuit 104 of the RPU 101 is preferably configured to turn ON the RPU switch K3 only, after the second RPU switch K2 has been turned ON, and if the current Ii flowing here on the first power line 103a is above a third threshold value for a predetermined amount of time. This implements the 'safe start up' of the system 100.

The RPU switch Kl is preferably configured to be manually controlled, but it could also be auto-controlled by another manual switch (not shown). The RPU switch Kl serves as a further safety measure, since the control circuit 104 of the RPU 101 is preferably configured to turn ON the RPU switch K2 only, if the RPU switch Kl is turned ON. That is, for starting-up the system, at first the RPU switch Kl needs to be manually controlled (directly or indirectly), and then the 'safe start up' procedure is performed. Only then, the RPU switch K3 is turned ON, and the HVDC voltage is supplied across the power lines 103.

In FIGs 3 and 4, the RPR 102 includes a capacitor CI, in order to buffer voltage changes within the RPR 102, and includes a second RPR switch K4. This RPR switch K4 is also controlled by the control circuit 106 of the RPR 102. In particular, the RPR switch K4 is preferably turned ON by default, and in this condition it connects a resistance Rl in parallel to the two power lines 103. The RPR switch K4 is turned OFF by the control circuit 106, after the control circuit 106 of the RPR 102 is powered for a predetermined amount of time. Thus, the RPR switch K4 is turned OFF after 'safe start up'.

FIG. 5 shows schematically the 'safe start up' procedure of the HVDC system 100 shown in the FIGs 3 and 4. At first, the RPU switch Kl is turned ON, preferably manually. Then, the RPU switch K2 is turned ON, and the 'safe start up' procedure starts. If the current Ii on here the power line 103 a rises above the (third) threshold value, which is preferably 200mA, the RPU switch K2 is turned OFF, and the RPU switch K3 is turned ON for entering normal working operation. FIG. 6 shows this normal working operation of the HVDC system 100 of the FIGs 3 and 4. A load is connected and the system 100 operates as follows. The upper diagram in FIG. 6 shows that the RPR switch Q 1 of the RPR 102 is controlled by the control circuit 106 to be periodically ON, with an on-time TON, and OFF, with an off-time TOFF. If the RPR switch Ql is ON, a certain predetermined work current flows through the RPR 102 on the two power lines 103. If the RPR switch Ql is OFF, approximately no current flows on the two power lines 103 through the RPR 102.

FIG. 7 shows an 'open circuit detection' for the HVDC system 100 shown in the FIGs 3 and 4. An open circuit fault, like a broken cable of the power lines 103, happens at a specific point in time - as indicated by the arrow. If this fault happens, the detected current Ii drops to nearly zero, and accordingly below or equal to a (first) threshold value during a complete time period, i.e. during an on-time and an off-time of the RPR switch Ql . In this scenario, the (first) threshold value is preferably 2- 15mA, as shown more preferably 10mA.

FIG. 8 shows how a 'touch both poles condition' is detected in the HVDC system 100 of the FIGs 3 and 4. A load is connected and both poles (i.e. power lines 103) are touched simultaneously. Again, the related fault happens at some specific time - as indicated in the upper diagram of FIG. 8. If such fault happens, the current Ii remains above a certain (second) threshold value, even if the RPR switch Ql is turned OFF. That is, the current Ii flowing on the power line 103a is above the (second) threshold value during a complete predetermined time period. In this scenario, the (second) threshold value is preferably 20-50mA, as shown more preferably 30mA. FIG. 9 shows a method according to an embodiment of the present invention, which builds on the method shown in FIG. 2. The method of FIG. 9 is carried out by the HVDC system 100 of the FIGs 3 and 4, respectively. It can be seen from FIG. 9 that after a 'safe start up' procedure, a normal operation of the system 100 is entered. In particular, the normal operation includes Open circuit detection' and 'touch both poles detection'. Therefore, if in a complete predetermined period the current Ii is 'fault', i.e. is always below exemplarily 10mA, the RPU switch K3 is turned OFF. The RPU switch K3 is also turned OFF, if in the complete predetermined time period the current Ii is above exemplarily 30mA.

FIG. 10 shows another embodiment of a system 100 according to the present invention, which builds on the embodiment of FIG. 3. Likewise, FIG. 11 shows an HVDC system 100 building on the system 100 shown in FIG. 4. In the systems 100 shown in the FIGs 10 and 11 , respectively, the RPU 101 comprises a second determining unit 1000, which is configured to determine a current I2/I1 flowing on a second power line 103b/103a of the two power lines 103. Here, as an example only, it determines the current I 2 flowing on the power line 103b. That means, current is now separately detected by the determining units 105 and 1000 on both power lines 103a and 103b. Both determining units 105 and 1000 measure the current directly.

Here, in the FIGs 10 and 11, the control circuit 104 of the RPU 101 is configured to turn OFF the RPU switch K3, if the current Ii flowing on the first power line 103a is below or equal to the first threshold value during a complete predetermined time period, or if either one of the currents I 2 andli flowing on the two power lines 103 is above the second threshold value during a complete predetermined time period. Otherwise, the systems 100 of FIGs 10 and 11 are similar to the systems 100 of FIGs 3 and 4.

FIG. 12 shows 'safe start up' procedure of the HVDC system 100 of the FIGs 10 and 11. The 'safe start up' procedure is identical to the one shown in FIG. 5 with respect to the systems 100 of the FIGs 3 and 4 with one exception. Now in FIG. 12 both currents Ii and I 2 are detected to be above the threshold value of preferably 200mA, before the normal working mode starts.

FIG. 13 shows the normal working mode of the HVDC system 100 of FIGs 10 and 11. In a similar manner as for the system of FIGs 3 and 4, in the normal working mode the RPR switch Ql of the RPR 102 is turned ON and OFF periodically. If the RPR switch Ql is ON, a certain work current flows on both power lines 103, i.e. both currents Ii and I2 reach their nominal working value. If the RPR switch Ql is turned OFF, both currents Ii and I2 are nearly zero. FIG. 14 shows the Open circuit detection'. If the related fault happens (arrow), regardless of the RPR switch Q 1 , both currents Ii and h stay nearly zero for at least a complete predetermined time period. In this case, the condition is detected.

FIG. 15 shows the 'touch both poles detection' as carried out by the system 100 of the FIGs 10 and 11, respectively. After the related fault happens, both currents Ii and h on the two power lines 103 do not drop any more all the way to nearly zero, but stay above a certain current value. Here, if both currents are above the predetermined (second) threshold value of most preferably 30mA, the condition of touching both poles is detected.

FIG. 16 shows 'residual current detection', which is only possible with having the two current determining units 105 and 1000. A related fault happens at some point in time (arrow), and if the fault happens, certain observations can be made with respect to the currents Ii and h. Current Ii is in this case not affected. Current h exhibits, however, a residual current of above the (second) threshold value of preferably 30mA, even in the off-times defined by the RPR switch Ql . Notably, the situation could be vice versa with respect to the two currents. Accordingly, if the current Ii flowing on the first power line 103a and/or the current h flowing on the second power line 103b is above the (second) threshold value during a complete predetermined time period, the RPU switch K3 is turned OFF.

FIG. 17 shows a method according to an embodiment of the present invention building on the method shown in FIG. 2. The method shows the operation of the HVDC system 100 of FIGs 10 and 11, and is similar to the method of FIG. 9. In normal operation, now also 'residual current detection' is carried out. That means that if, in a predetermined time period, one of the currents Ii and h is correct, and the other one is 'fault', (here above 30mA), the RPU switch K3 is turned OFF.

FIG. 18 shows another embodiment according to the present invention, which builds on the embodiment of the HVDC system 100 shown in FIG. 1. FIG. 19 shows correspondingly the same system 100 with both voltages supplied by a single converter 401 in the RPU 101.

In both HVDC systems 100 of the FIGs 18 and 19, the first determining unit 105 is now a voltage measuring unit, which measures the current flowing on the power line 103 indirectly. In particular, the voltage measuring unit 105 is configured to measure a voltage VDI provided by a first diode Di. The first diode Di is here exemplarily configured to provide a first voltage value, if the current Ii flowing on the first power line 103a is equal to a first threshold value, and is configured to provide a second voltage value, if the current Ii flowing on the first power line 103a is above a second threshold value. In the HVDC system 100 of the FIGs 18 and 19, the first threshold value is here preferably between 0 and 5mA, and is more preferably 0mA. The second threshold value is here preferably between 0 and 5mA, and is more preferably also 0mA. The voltage VDI provided by the first diode Di, if a current Ii is flowing, is preferably 0.7V and otherwise, if no current Ii is flowing, is preferably 0V. In other words, a more or less digital scenario, i.e. whether a current Ii is flowing on the power line 103a or not, is detected.

The diode Di may be a Ge diode or a Si diode. FIG. 20 shows 'safe start up' of the HVDC system 100 shown in FIGs 18 and 19, which works in a similar manner as the 'safe start up' shown in FIG. 5. However, here the 'safe start up' procedure is completed, if the voltage VDI of the diode Di is above, for example, 0.7V. The FIGs 21, 22 and 23 show normal working mode, 'open circuit detection', and 'touch both poles detection' of the system 100 of FIGs 18 and 19, respectively. In normal working mode, depending on the RPR switch Ql, the voltage VDI switches between 0.7V (on-time) and nearly zero (off-time). If the open circuit condition occurs, the voltage VDI drops to nearly zero for a complete predetermined time period. That also means that the current Ii flowing on the power line 103a, on which the diode Di is provided, is below or equal to a threshold current during a complete predetermined time period. If the touch both poles condition is detected, the voltage VDI stays above or near 0.7V for the complete predetermined time period, which also means that the current Ii flowing on the power line 103a, on which the diode Di is provided, is above a certain current value during a complete predetermined time period, i.e. does not drop to zero.

FIG. 24 shows a method according to an embodiment of the present invention, which builds on the method shown in FIG. 2. The method of FIG. 24 is similar to the method shown in FIG. 9, but is adapted to the operation of the system 100 shown in FIGs 18 and 19. Since only one diode Di is provided as the determining unit 105, only 'open circuit detection' and 'touch both poles detection' is possible with this simplified version of the system 100 incorporating a voltage method. The RPU switch K3 is turned OFF either, if VDI is always preferably zero, of if VDI is always preferably 0.7V.

FIGs 25 and 26 show HVDC systems 100 according to an embodiment of the present invention, building on the FIGs 18 and 19, respectively. In order to also allow 'residual current detection', here also a second diode D 2 is provided on the other power line 103b. Preferably, the diode D 2 is identical to the diode Di. In any case, the second diode D 2 is again configured to provide a first voltage value, here exemplarily if the current I 2 flowing on the power line 103b is equal to the (first) threshold value, and is configured to provide a second voltage value, if the current I 2 flowing on the power line 103b is above the (second) threshold value. As above for FIGs 18 and 19, the second threshold value is preferably equal to the first threshold value, and is most preferably 0mA. The FIGs 27 to 31 show 'safe start up', normal working mode, 'open circuit detection', 'touch both poles detection', and 'residual current detection', respectively, of the system 100 shown in FIGs 25 and 26. These are identical to the system 100 of FIGs 18 and 19, respectively. In contrast to the system 100 shown in FIGs 18 and 19, the system 100 of FIGs 25 and 26 is also able to carry out 'residual current detection', which is specifically shown in FIG. 31. In this case, if a related fault happens (arrow), one of the voltages VDI and VD2, in this case VDI behaves normally, and the other voltage, in this case VD2, remains at the higher voltage value of preferably 0.7V for a complete predetermined time period. Then the condition is detected.

Accordingly, FIG. 32 shows a method according to an embodiment of the present invention building on the method 200 shown in FIG. 2. The method is similar to the method in FIG. 24, but the system 100 now in normal operation is also able to perform 'residual current detection'. That means, if in a complete predetermined time period one of the voltages VDI and VD2 is correct and the other one is 'fault', i.e. is 0.7V in this case, the RPU switch K3 is turned OFF.

In summary, the present invention presents a HVDC system 100 operating a method 200, particularly either a 'current method' (system 100 of FIGs 3, 4, 10 and 11) or 'voltage method' (system 100 of FIGs 18, 19, 25 and 26), in order to achieve 'safe start up', 'open circuit detection', 'touch both poles detection', and potentially 'residual current detection'. These detections help significantly to prevent electrical shocks in the FJVDC systems 100. The present invention is intended to be applied to systems with a higher voltage than 48Vdc, which is used in conventional ICT equipment. In particular, the voltage is as defined in ITU L.1200 and this the voltage range is preferably 192Vdc-410Vdc.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.