Power System

Abstract

The power system includes a DC voltage bus (101, 102) and at least two bus-tie links (103-105), each connected between the DC voltage buses. Each bus-tie link includes at least one capacitor (106-111) between a positive pole and a negative pole of the bus-tie link. At least one pole of each bus-tie link is connected to a respective pole (118, 119) of the DC voltage bus via an overcurrent protection device (112-117), such as a fuse. The capacitors of the bus-tie links form a distributed capacitor storage capable of supplying fault current to the power system and operating the overcurrent protection device such that zone selectivity is achieved. The power system may be, for example, a power system of a ship or another vessel.

Description

[Technical Field]

[0001] The present disclosure relates to a power system which may be, for example, but not necessarily, a power system of a ship or another vessel. [Background technology]

[0002] Power systems often include two or more DC voltage buses configured to supply electrical energy to loads and that are required to maintain operability independently of one another. The power system may, for example, be the power system of a ship or another vessel, in which case the loads of the power system may, for example, include one or more propulsion motors, the ship's AC voltage network, and other loads, such as one or more bow thruster motors. The motors are advantageously alternating current (AC) motors, and the corresponding load converters are inverters for converting the DC voltage of the DC voltage buses into AC voltages suitable for the AC motors. Summary of the Invention [Problem to be solved by the invention]

[0003] Cost-effective designs of power systems of the type referenced above often rely heavily on power flow through interconnected DC voltage buses for normal operation, while still allowing for fault operation even when the DC voltage buses are disconnected. In a typical design, the DC voltage buses are interconnected with bus-tie links during normal operation, and the bus-tie links are provided with overcurrent protection devices, such as fuses or overcurrent relays, to disconnect the DC voltage buses from each other during a fault condition. However, maintaining zone selectivity in overcurrent protection in connection with power systems of the type referenced above can be difficult because, for example, if a fault occurs in a bus-tie link, fault current can flow from both DC voltage buses to the fault, and the overcurrent protection devices connecting the bus-tie links to the DC voltage buses each pass only a portion, e.g., approximately half, of the fault current. Thus, in DC voltage electrical systems where the availability of short circuit current is limited and / or provided by DC voltage capacitors in the system, high power rated bus-tie links require a large amount of capacitance on the DC voltage bus to provide the energy necessary to activate overcurrent protection devices, for example, to blow fuses located in the bus-tie link. [Means for solving the problem]

[0004] The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention, nor is it intended to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of example embodiments of the invention.

[0005] In accordance with the present invention, a new power system is provided which may be, for example, but not necessarily, the power system of a ship or another vessel.

[0006] A power system according to the present invention includes a first DC voltage bus and a second DC voltage bus, and at least two bus-tie links each connected between the first DC voltage bus and the second DC voltage bus; each of the bus-tie links includes at least one capacitor between a first pole and a second pole of the bus-tie link; and at least a first pole of each of the bus-tie links is connected to a first pole of the first DC voltage bus and a first pole of the second DC voltage bus via an overcurrent protection device, e.g., a fuse or an overcurrent relay, each of the overcurrent protection devices configured to interrupt current in response to an overcurrent condition at the overcurrent protection device;

[0007] The capacitors of the bus-tie link form a distributed capacitor storage that can supply fault current to the power system and operate overcurrent protection devices so that zone selectivity is achieved. The first pole of the bus-tie link and the first pole of the first DC voltage bus and the first pole of the second DC voltage bus can be, for example, a positive pole of the bus-tie link and a positive pole of the first DC voltage bus and a positive pole of the second DC voltage bus. However, the first pole can also be a negative pole.

[0008] According to the invention, there is also provided a new ship comprising an electrical power system according to the invention. The loads of the ship's electrical power system may include, for example, one or more propulsion motors, the ship's AC voltage network, and / or other loads, such as, for example, one or more bow thruster motors. The motors are advantageously alternating current "AC" motors, and the corresponding load converter is an inverter for converting a DC voltage into an AC voltage suitable for the AC motors.

[0009] Exemplary, non-limiting embodiments are set forth in the accompanying dependent claims.

[0010] Various exemplary and non-limiting embodiments, both as to structure and method of operation, together with additional objects and advantages thereof, can be best understood from the following description of specific exemplary and non-limiting embodiments when read in connection with the accompanying drawings.

[0011] The verbs "to comprise" and "to include" are used in this specification as open limitations which neither exclude nor require the presence of any unrecited features. Features recited in the dependent claims may be freely combined with each other unless expressly stated otherwise. Furthermore, it is to be understood that the use of "a" or "an", i.e., the singular, throughout this specification does not exclude the plural.

[0012] Exemplary, non-limiting embodiments and their advantages are described in more detail below, by way of example and with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0013] [Figure 1] 1 illustrates a schematic diagram of a power system in accordance with an exemplary and non-limiting embodiment; [Figure 2] 1 illustrates a schematic diagram of a power system in accordance with an exemplary and non-limiting embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0014] The specific examples provided herein below are not to be construed as limiting the scope and / or applicability of the appended claims. The lists and groups of examples provided herein below are not exhaustive unless expressly stated to the contrary.

[0015] FIG. 1 shows a schematic diagram of an electric power system according to an exemplary and non-limiting embodiment. In this exemplary case, the electric power system is a power system of a vessel 132, which may be, for example, a ship. The electric power system includes a first direct current voltage bus 101 and a second direct current voltage bus 102. In the exemplary power system illustrated in FIG. 1, a power supply connected to the first direct current voltage bus 101 includes a battery device 131 configured to supply electric energy to the first direct current voltage bus 101 via a direct current voltage-to-direct current voltage (DC-DC) converter 132 and via an overcurrent protection device 133. However, the electric power system according to an exemplary and non-limiting embodiment may also include, for example, a generator and / or a fuel cell in addition to or instead of the battery device. In the exemplary case illustrated in FIG. 1, the overcurrent protection device 133 is a fuse, but the overcurrent protection device 133 may also be an overcurrent relay.

[0016] The first DC voltage bus 101 includes power outlets, each configured to supply power to a load of the power system and equipped with an overcurrent protection device. In FIG. 1 , one of the power outlets is designated by reference numeral 128, and the overcurrent protection device of the power outlet 128, such as a fuse or an overcurrent relay, is designated by reference numeral 130. The load supplied by the power outlet 128 is designated by reference numeral 129. In this exemplary case, the load 129 includes an alternating current (AC) propulsion motor 135 and an inverter 134 for converting the DC voltage of the first DC voltage bus 101 to an AC voltage suitable for the propulsion motor 135. Additionally, the first DC voltage bus 101 includes another power outlet for supplying electrical energy to a load including at least a portion of an alternating current (AC) network 136 of the vessel 132. 1, the power supplies and loads connected to the second DC voltage bus 102 are the same power supplies and loads connected to the first DC voltage bus 101. However, the first DC voltage bus and the second DC voltage bus may also be connected to different power supplies and / or different loads.

[0017] The power system includes bus-tie links, each connected between a first DC voltage bus 101 and a second DC voltage bus 102. In the exemplary case illustrated in FIG. 1 , the power system includes three bus-tie links 103, 104, and 105. However, a power system according to an exemplary and non-limiting embodiment may also include only two bus-tie links between two DC voltage buses, or may include four or more bus-tie links. Each bus-tie link includes a capacitor between the first and second poles of the bus-tie link. Bus-tie link 103 includes capacitors 106 and 107, bus-tie link 104 includes capacitors 108 and 109, and bus-tie link 105 includes capacitors 110 and 111. On each bus-tie link, the two capacitors are advantageously located near the ends of the bus-tie link under consideration, so that the majority of the physical length of the bus-tie link is between the two capacitors. Each capacitor may include, for example, one or more electric double layer capacitor (EDLC) elements.

[0018] A first pole of each of the bus-tie links 103-105 is connected to first poles 118 and 119 of the first DC voltage bus 101 and the second DC voltage bus 102 via overcurrent protection devices, such as fuses or overcurrent relays. The first poles may be, for example, positive voltage poles. Each overcurrent protection device is configured to interrupt current in response to an overcurrent condition of the overcurrent protection device under consideration. The bus-tie link 103 is connected to first poles 118 and 119 of the first DC voltage bus 101 and the second DC voltage bus 102 via overcurrent protection devices 112 and 113. Similarly, bus-tie link 104 is connected to first poles of the first and second DC voltage buses via overcurrent protection devices 114 and 115, and bus-tie link 105 is connected to first poles of the first and second DC voltage buses via overcurrent protection devices 116 and 117.

[0019] For illustrative purposes, consider an exemplary fault situation in which one of the bus-tie links has a fault, e.g., a short circuit or a wire short to ground. Without limiting generality, consider a fault situation in which bus-tie link 105 has a fault 137. In this exemplary case, current is supplied to fault 137 by capacitors 110 and 111. Furthermore, current is supplied to fault 137 by capacitor 126 of first DC voltage bus 101 via overcurrent protection device 116 and by capacitor 127 of second DC voltage bus 102 via overcurrent protection device 117. Furthermore, current is supplied to fault 137 by capacitors 106 and 107 of bus-tie link 103 via overcurrent protection devices 112, 113, 116, and 117. Furthermore, current is being supplied to fault 137 by capacitors 108 and 109 of bus-tie link 104 through overcurrent protection devices 114, 115, 116, and 117. Thus, the total current through overcurrent protection devices 116 and 117 includes current from multiple power sources, so overcurrent protection devices 116 and 117 interrupt the current before overcurrent protection devices 112-115 conduct enough current for long enough for overcurrent protection devices 112-115 to react, thereby isolating bus-tie link 105 and fault 137 from the rest of the power system.

[0020] Consider now an exemplary fault situation in which one of the DC voltage buses has a fault. Without limiting generality, consider a situation in which there is a fault 138 in the first DC voltage bus 101. In this exemplary case, current is supplied to the fault 138 by the capacitor 126. Furthermore, current is supplied to the fault 138 by the capacitors 106-111 through the overcurrent protection devices 112, 114, and 116. As a corollary, the overcurrent protection devices 112, 114, and 116 interrupt the current, thereby disconnecting the first DC voltage bus 101 from the second DC voltage bus 102.

[0021] As illustrated by the exemplary fault conditions presented above, the capacitors 106-111 of the bus-tie links 103-105 form a distributed capacitor storage that can supply fault current to the power system and operate overcurrent protection devices such that zone selectivity is achieved.

[0022] 2 shows a schematic diagram of a power system according to an exemplary and non-limiting embodiment. The power system includes a first DC voltage bus 201 and a second DC voltage bus 202. The power system includes three bus-tie links 203, 204, and 205, each connected between the first DC voltage bus 201 and the second DC voltage bus 202. Each of the bus-tie links includes a capacitor between a first pole and a second pole of the bus-tie link. Bus-tie link 203 includes capacitor 206, bus-tie link 204 includes capacitor 208, and bus-tie link 205 includes capacitor 210. A first pole of each of the bus-tie links 203-205 is connected to first poles 218 and 219 of the first DC voltage bus 201 and the second DC voltage bus 202 via overcurrent protection devices 212, 213, 214, 215, 216, and 217, e.g., fuses or overcurrent relays. Similarly, a second pole of each of the bus-tie links 203-205 is connected to second poles 226 and 227 of the first DC voltage bus 201 and the second DC voltage bus 202 via overcurrent protection devices 220, 221, 222, 223, 224, and 225. In the exemplary power system illustrated in FIG. 2, the first pole is a positive pole and the second pole is a negative pole. In the example power system illustrated in FIG. 2 , the bus-tie link includes a switch disconnector 231 for disconnecting the electrical connection implemented in the bus-tie link between the first DC voltage bus 201 and the second DC voltage bus 202.

[0023] The specific examples provided herein above should not be construed as limiting the applicability and / or interpretation of the appended claims. The lists and groups of examples provided herein above are not exhaustive unless expressly stated to the contrary.

Claims

1. In a power system including a first DC voltage bus and a second DC voltage bus (101, 102, 201, 202), the power system further comprises at least two bus-tie links (103-105, 203-205) each connected between the first DC voltage bus and the second DC voltage bus; each of said bus-tie links includes at least one capacitor (106-111, 206, 208, 210) between a first pole and a second pole of said bus-tie link; and - at least the first pole of each of the bus-tie links is connected to first poles (118, 119, 218, 219) of the first DC voltage bus and the second DC voltage bus via overcurrent protection devices (112-117, 212-217), each of the overcurrent protection devices being configured to interrupt current in response to an overcurrent condition of the overcurrent protection device.

2. 2. The power system of claim 1, wherein the second pole of each of the bus-tie links is connected to second poles (226, 227) of the first DC voltage bus and the second DC voltage bus via other overcurrent protection devices (220-225).

3. 3. The power system of claim 1, wherein each of the bus-tie links includes two capacitors, each capacitor being between the first pole and the second pole of the bus-tie link.

4. 4. The power system of claim 3, wherein the two capacitors are near ends of the bus-tie link such that a majority of the physical length of the bus-tie link is between the two capacitors.

5. 5. The power system of claim 1, wherein the first DC voltage bus includes a capacitor between the first pole of the first DC voltage bus and a second pole of the first DC voltage bus.

6. 6. The power system of claim 1, wherein the second DC voltage bus includes a capacitor between the first pole of the second DC voltage bus and the second pole of the second DC voltage bus.

7. 7. The power system of claim 1, wherein each of the first DC voltage bus and the second DC voltage bus includes at least one power outlet (128) provided with an overcurrent protection device (130) and suitable for supplying power to a load of the power system.

8. The power system of any one of claims 1 to 7, wherein each capacitor of each of the bus-tie links comprises one or more electric double layer capacitor elements.

9. The power system of any preceding claim, wherein the overcurrent protection device comprises a fuse.

10. 10. The power system of claim 1, wherein each of the bus-tie links includes a switch-disconnector (231) for disconnecting an electrical connection implemented at the bus-tie link between the first DC voltage bus and the second DC voltage bus.

11. A vessel (132) comprising an electrical power system according to any one of claims 1 to 10.

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