Arrangement and procedure for a power collection line

Abstract

Direct current (DC) power distribution arrangement comprising a plurality of DC power distribution subsystems (DC 51 , DC 52 ), where each DC power distribution subsystem (DC 51 , DC 52 ) an inverter unit (INU 51 , INU 52 ) designed to operate as a subsystem-specific circuit breaker for connecting / disconnecting the DC power distribution subsystem (DC 51 , DC 52 ) with / from the rest of the DC power distribution arrangement, characterized in that the DC power distribution arrangement comprises two DC power distribution subsystems (DC 51 , DC 52 ) and two inverter units (INU 51 , INU 52 ), wherein the inverter units (INU 51 , INU 52 ) are designed to act as pole-specific circuit breakers between corresponding poles (+,-) of the two DC power distribution subsystems (DC 51 , DC52 ) in such a way that: a first pole (+) of the first DC power distribution subsystem (DC 51 ) with a DC connection of the first inverter unit (INU 51 ) and a corresponding first pole (+) of the second DC power distribution subsystem (DC 52 ) with interconnected AC connections of the first inverter unit (INU 51 ) and a second pole (-) of the first DC power distribution subsystem (DC 51 ) with interconnected AC connections of the second inverter unit (INU 52 ) and a corresponding second pole (-) of the second DC power distribution subsystem (DC 52 ) with a DC connection of the second inverter unit (INU 52 ) is connected.

Description

Technical area

[0001] The object of this invention relates to a power bus assembly and a method for a power bus assembly. In particular, the object of the present invention is an assembly and a method for using an inverter unit as a circuit breaker device for connecting / disconnecting a number of direct current (DC) power distribution busses. State of the art and description of the problem

[0002] CN 1 04 967 111 A describes a topological structure of a multi-channel DC transformer station. WO 2014 / 125 279 A2 describes an electronic p-phase hub for transferring power between N DC systems using DC voltage. US 2015 / 0 137 595 A1 describes a hybrid AC / DC distribution system for multi-story buildings. US 2013 / 0 200 714 A1 describes a medium-voltage DC collection system.

[0003] In large power electronics installations, power distribution means are required between power supplying / generating devices and power consuming devices. Due to the widespread use of frequency converter technology, in which a rectifier unit and an inverter unit are connected via a DC link, it is common practice to use a DC power bus as a distribution channel between a number of power-generating devices and power consuming devices.

[0004] In certain environments, such as ship installations, there is also a need to divide the power distribution system into several smaller subsystems. For redundancy reasons, the subsystems must be interconnectable and separable via so-called DC bus coupling switches, e.g., to prevent a complete power outage due to a local catastrophic failure that could cause the voltage of the power distribution bus to collapse.

[0005] An electromechanical circuit breaker is the device typically used to connect / disconnect various power bus lines. However, interrupting direct current can be problematic due to the continuous arc generated during contact opening. Therefore, a DC circuit requires a dedicated circuit breaker, which is expensive. Due to the mechanical operating principle, the circuit breaker is relatively slow, which can be a problem when trying to avoid widespread power distribution disturbances, such as in the event of a local short circuit. Brief description of the invention

[0006] The object of this invention is an arrangement and method that avoids the disadvantages of electromechanical circuit breakers and that can be used for connecting / disconnecting a number of DC power bus lines, e.g., as a coupling switch in ship installations. This object is achieved by the arrangements characterized by what is stated in the characterizing part of the independent claims. Other preferred embodiments of the invention are the objects of the dependent claims.

[0007] The fundamental principle of the present invention is that similar inverter units (INUs) such as those used in frequency converters for motor speed control systems or in active input stage (AFE) converters are used as circuit breakers in DC power distribution systems. Using a standard INU in this context means utilizing the same hardware (i.e., power and control electronics circuitry and mechanics), whereas the software that determines how the controllable power breakers are controlled is specific to this application. It is understood that parallel-connected INUs, whose arrangement can be used to increase the current interrupting capacity, logically correspond to one INU in this context.

[0008] According to a first embodiment of the invention, the DC terminals of each INU belonging to the system are connected to an INU-specific DC power distribution bus, and the INUs are interconnected using connecting links between their AC terminals. A connecting link can be, for example, a busbar or a power cable, and it can include an inductive component to limit transient currents in switching situations. The installation of connecting links is permanent, although only a portion may be selected as being in use at a time by controlling the controllable power switches of INUs according to the invention.

[0009] According to a second embodiment of the invention, each of the three AC phase terminals of an INU belonging to the system is connected to a phase-specific connecting element.

[0010] In an embodiment related to the second embodiment, the controllable power switches of INUs are controlled such that only a portion of the links, e.g., two of the three links, are in use at a time. In a static mode of operation, the same links are used continuously, and in a dynamic mode of operation, the connection sequences are rotated such that the average load of each phase is substantially equal to balance the load. Implementing the dynamic mode of operation requires the presence of a higher-level controller capable of turning on / off any controllable power switches, such as IGBTs, in any INU belonging to the system.

[0011] In another embodiment related to the second embodiment, the controllable power switches of INUs are controlled such that all three links are in use all the time, with one of them connected to the positive poles of all DC power distribution systems and the other two to the negative poles, or vice versa. Also, in this embodiment, either a static or dynamic operating mode can be used.

[0012] According to a third embodiment of the invention, the number of interconnects is such that the AC terminals of each INU can be connected to a different, unique combination of interconnects. For example, in the case of 3 or 4 power bus lines and INUs with 3 AC connections, this combination requirement requires that the number of interconnects be at least 4; in the case of 5 power bus lines, at least 5 interconnects are required, and so on.

[0013] With the third embodiment, both a static and a dynamic operating mode are possible. In an embodiment related to this third embodiment, the power switches of the INUs are controlled such that, in the event of a catastrophic failure that collapses a DC power bus voltage and shorts three links, the connection between the undamaged DC power buses is maintained.

[0014] In the fourth embodiment of the invention, two DC power distribution busses are interconnected by two INUs such that one INU is connected between the positive poles of both busses and another INU is connected between the negative poles. In this connection, a DC terminal of one INU is connected to a DC power distribution bus pole, and all three AC phase terminals are connected in parallel to the corresponding pole of another DC power distribution bus. The INUs are connected such that the conduction direction of the freewheeling diodes in both INUs is the same, with the effect that if no controllable power switch, e.g., IGBT, is switched on, there is no balancing path between the busses, which are thus disconnected in this situation.

[0015] In an embodiment related to the fourth embodiment, the controllable power switches of an INU are controlled so that all three phase switches are always in the same position.

[0016] In an embodiment related to all previous arrangements, all other DC links can be initially charged by an inverter connected to an externally fully charged DC power bus by adjusting its pulse-width modulated output voltage to smoothly ramp to full-level. As one skilled in the art will appreciate, implementing this method requires links with some inductance to limit charging current pulses due to the full-level voltage pulses.

[0017] In an embodiment related to all previous arrangements, all controllable power switches, e.g., IGBTs, of one or more INUs can be continuously off. In this case, DC power can flow via the freewheeling diodes only in the direction of the power subsystems connected to these INUs (i.e., a unidirectional power flow).

[0018] In an embodiment related to all previous arrangements, the internal load current measurement of standard INUs is utilized by switching off one or all controllable power switches, such as IGBTs, in the event of a measured overcurrent. If all controllable power switches are switched off, only one-way power flow is enabled. If only the controllable power switch that carried the overcurrent is switched off, operation can continue by energizing another link via a different AC phase connection. In this case, the controllable power switches connected to the overloaded link in other INUs are also switched off, and corresponding (upper or lower branch) controllable switches in another phase of all INUs connected to a common link are switched on.

[0019] The present invention makes it possible to implement a short-circuit-proof DC power breaker function by utilizing a technology widely used in the power electronics industry. The connection / disconnection time of DC power distribution busbars is faster and requires lower costs than using prior art electromechanical switches. If the system includes an upper control device, the dynamic operation mode can be implemented by alternating the connection sequence of different linking elements and phase switches of INUs to balance the load. From a field service perspective, it is beneficial to use the same power modules in DC power breakers as in motor drivers and active input stage converters. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following, the invention will be described in more detail with the aid of some examples of its embodiments with reference to the attached drawings, in which Fig. 1 shows the main circuit of a frequency converter control, Fig. 2 shows a single-line diagram of a DC power distribution bus system, Fig. 3A illustrates an arrangement in a DC power distribution bus system according to the first embodiment of the invention, Fig. 3B illustrates timing diagrams related to the first embodiment of the invention, Fig. 4A illustrates an arrangement in a DC power distribution bus system according to the second embodiment of the invention, Fig. 4B illustrates a timing diagram related to the second embodiment of the present invention, and Fig. 5 illustrates an arrangement in a DC power distribution bus system according to the third embodiment of the invention. Detailed description of the invention

[0021] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms "first," "second," and the like, as used herein, do not indicate order, quantity, or importance, but are used merely to distinguish one item from another. Also, the term "a(n)" does not indicate a limitation of a quantity, but rather indicates the presence of at least one of the referenced item. The use of "including," "comprising," or "having" and variations thereof herein is intended to mean to include the items listed thereafter and their equivalents, as well as additional items.The terms "connected" and "coupled" are not limited to physical or mechanical connections or couplings and can include electrical connections or couplings, whether direct or indirect. Furthermore, the terms "circuit" and "circuitry" and "controller" can include either a single component or a plurality of components, either active and / or passive, that are connected or otherwise coupled to provide the described function.

[0022] Fig. 1 presents a simplified main circuit diagram of a known and typical regenerative frequency converter as an example in which the power units utilized in circuit breaker arrangements according to the present invention can be commonly used.

[0023] In the example, the converter includes an active input bridge AFE, which is capable of transferring energy in both directions between the 3-phase power grid R, S, T and the DC link DC. AFE is connected to the grid via a so-called LCL line filter unit LFU, which includes a first 3-phase choke unit LF1, a second 3-phase choke unit LF2, and a capacitor unit C F The inverter unit INU generates DC from the DC voltage circuit, which is fed through a capacitor C D1filtered, an adjustable pulse-width modulated (PWM) 3-phase output voltage U, V, W to power an AC motor M. The AFE and INU bridges are similar, both consisting of 3-phase switches capable of connecting the phase terminal to both poles DC+ and DC- of the DC link. A phase switch consists of upper-branch power components (i.e., a controllable switch, typically an IGBT with an anti-parallel diode) connected to DC+ and similar power components in the lower-branch connected to DC.

[0024] Fig. Figure 2 shows an exemplary single-line drawing of a DC power distribution system in which inverter units and converters with active input stage, as in Fig. 1. In this example, the DC power distribution system is divided into two subsystems DC1, DC2, which can be connected or separated by a circuit breaker S1.

[0025] DC1 is powered by a diesel generator DG via an asynchronous generator ASG, a line filter unit LFU1, and an active input stage converter AFE1. A motor control system comprising an inverter unit INU1 and a motor M1 (which, for example, drives an air conditioning fan) is an example of a typical load that can be connected to the system. A battery may be connected to the system to ensure power stability (B1 via a voltage level adjustment converter DC / DC1).

[0026] In this example, DC2 is powered from the mains supply G2 via a transformer T2, a line filter unit LFU2, and a converter with an active input stage AFE2. Several motor controllers (INU2, M2, INU3, M3) are connected to DC2.

[0027] Fig. Figure 3A illustrates an arrangement according to the present invention, such as any number of DC power distribution busbars, in this case three DC busbars 31 , DC 32 , DC 33 can be connected or disconnected by three connecting links A, B, C and inverter units specific to the DC bus INU 31 , INU 32 , INU 33 used as a circuit breaker. The DC terminals +, - of each INU are coupled to the corresponding DC bus terminals, and their AC terminals U, V, W are coupled to the phase-specific connecting elements A, B, C.

[0028] Fig. Figure 3B illustrates two methods for coupling the DC power distribution bus lines in the arrangement of Fig. 3A. In the diagrams, a thick line with a + sign means that the connecting link is connected to the + pole of all DC power distribution busbars. In practice, the connection is made by turning on the upper-branch power component of the phase switch connected to the connecting link. For example, a thick A line with a + sign means that the controllable upper-branch power switches, such as IGBTs, of the U phase in all INUs are turned on. Similarly, for example, a thick B line with a - sign means that the controllable lower-branch power switches, such as IGBTs, of the V phase in all INUs are turned on. The dotted line in the diagram means that there is no connection between the DC busbars via the connecting link. For example, a dotted C line means that in W-phase switches, all controllable power switches, such as IGBTs, are turned off.

[0029] The upper part of Fig. Figure 3B illustrates a method in which only two links are in use at a time. To balance the average loads of power semiconductors and links, their operating sequences can be rotated at regular intervals at times t0, t1, t2, etc., as shown in the figure. This is referred to in this document as the dynamic loading method. It is also possible to use the static loading method by continuously operating only two links A and C during the time interval t0...t1 in Fig. 3B, and keeping the free part (B) as a spare. The spare part can be put into service in this example, for example, in a situation where link C suffers a ground fault, by turning off all controllable power switches, e.g., IGBTs, in the W phase and turning on corresponding controllable power switches in the V phase.

[0030] The lower part of Fig. Figure 3B illustrates a method in which all links are used continuously (i.e., all phase switches of all INUs are continuously active). To balance the average loads of power semiconductors and links, the durations during which two links are connected to the + poles of the DC busbars and one link to the - pole, or vice versa, are rotated at regular intervals t0, t1, t2, etc. A static loading method is also possible in this case by continuously using the same links.

[0031] Fig. Figure 4A illustrates an arrangement according to the present invention, such as any number of DC power distribution busbars, in this case five DC busbars 41 ...DC 45 can be connected or disconnected by five connecting elements D, E, F, G, H and inverter units specific to the DC bus INU41 ...INU 45 be used as a circuit breaker. The DC terminals +, - of each INU are coupled to the corresponding DC bus terminals, and their AC terminals U, V, W are coupled to the connecting links, so that each connection combination is different. The requirement for a different connection combination dictates the requirement regarding the number of connecting links; for example, in the case of 5 DC bus lines, the number of connecting links must be at least 5.

[0032] Fig. Figure 4B illustrates a method of connecting the DC power distribution busbars to DC 41 ... DC 45 In this method, each link is connected to the + or - pole of at least two DC bus lines. To balance the average loads of power semiconductors and link elements, their operating times can be reduced to the value specified above. Fig. 3B shown in a similar manner (rotation times t 10 , t 11 ). Instead of this dynamic loading procedure, a similar static loading procedure is used, as in the description of Fig. 3, is also possible in this case by using the same connecting links continuously.

[0033] The benefit of this arrangement and method is that a faulty DC bus can be isolated in such a way that the undamaged DC bus can remain connected and continue to operate normally. An example of this protection method is shown in Fig. Figure 4B illustrates that after time t 12 , to which the DC 41 The short circuit means that all connecting elements D, E, F are also short-circuited via the freewheeling diodes of INU 41are short-circuited. In a method embodiment related to this arrangement, the connecting links coupled to the faulty DC bus are connected to one of the poles of the undamaged DC bus (in this example, D, E, F are connected to the - pole) and the remaining connecting links are connected to the opposite pole (i.e., G and H are connected to the + pole).

[0034] Fig. Figure 5 illustrates an arrangement according to the present invention, such as two DC power distribution bus DC 51 , DC 52 can be connected or separated by connecting two inverter units INU 51 , INU 52be used as a circuit breaker. In the arrangement, the interconnected AC terminals of the first INU are connected to the + pole of the first DC bus, and the DC+ terminal is connected to the second DC bus. On the - pole side, the DC- terminal of another INU is connected to the first DC bus, and the interconnected AC terminals are connected to the second DC bus. The DC buses can be disconnected by turning off all controllable power switches, such as IGBTs, since then, due to the same conduction direction of the freewheeling diodes at both poles, no compensating current can flow between the DC buses. The DC buses can be interconnected by turning on the controllable power switches, whereby a compensating current can then flow via controllable power switches into one pole and diodes into another pole.Due to the parallel connected phase switches, the load capacity of the circuit breaker arrangement is maximum, which can be achieved by using a standard INU module.

[0035] In an embodiment related to this arrangement, the controllable circuit breakers of an INU are controlled so that all three phase switches are always in the same position.

[0036] Although the invention has been described with reference to the previous embodiment, it should be noted that the invention is not limited to this embodiment, but that many modifications and variations will be apparent to those skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

[1] Direct current (DC) power distribution arrangement comprising a plurality of DC power distribution subsystems (DC 51 , DC 52 ), where each DC power distribution subsystem (DC 51 , DC 52 ) an inverter unit (INU 51 , INU 52 ) designed to operate as a subsystem-specific circuit breaker for connecting / disconnecting the DC power distribution subsystem (DC 51 , DC 52 ) with / from the rest of the DC power distribution arrangement, characterized by that the DC power distribution arrangement comprises two DC power distribution subsystems (DC 51 , DC 52 ) and two inverter units (INU 51 , INU 52 ), wherein the inverter units (INU 51 , INU 52 ) are designed to act as pole-specific circuit breakers between corresponding poles (+,-) of the two DC power distribution subsystems (DC 51 , DC 52) in such a way that: a first pole (+) of the first DC power distribution subsystem (DC 51 ) with a DC connection of the first inverter unit (INU 51 ) and a corresponding first pole (+) of the second DC power distribution subsystem (DC 52 ) with interconnected AC connections of the first inverter unit (INU 51 ) and a second pole (-) of the first DC power distribution subsystem (DC 51 ) with interconnected AC connections of the second inverter unit (INU 52 ) and a corresponding second pole (-) of the second DC power distribution subsystem (DC 52 ) with a DC connection of the second inverter unit (INU 52 ) is connected. [2] DC power distribution arrangement according to claim 1 , characterized by , that the DC power distribution system includes an upper-level controller designed to control any controllable circuit breaker in any inverter (INU) connected to the system 51 , INU 52 ) on and / or off. [3] Direct current (DC) power distribution arrangement method, where the power distribution arrangement comprises several DC power distribution subsystems, each DC power distribution subsystem (DC 41 , DC 42 ) an inverter unit (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) includes a subsystem-specific circuit breaker for connecting / disconnecting the DC power distribution subsystem (DC 41 , DC) with / from the rest of the DC power distribution arrangement, with AC terminals (U, V, W) of the inverter units (INU 41 , INU 42 , INU 43 , INU44, INU 45) are coupled with connecting links (D, E, F, G, H), characterized by that in case of a measured overcurrent in an AC terminal (U, V, W) of an inverter unit (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) the link (D, E, F, G, H) connected to the AC terminal is de-energised by controlling the circuit breakers on the AC terminals (U, V, W) connected to the specific link (D, E, F, G, H) in all inverter units (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) are switched off, and another connecting link (D, E, F, G, H) by switching on corresponding controllable circuit breakers in another AC terminal (U, V, W) of all inverter units (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) is energized. [4] Direct current (DC) power distribution arrangement method according to claim 3, characterized by that the inverter units (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) controllable circuit breakers simultaneously in an on-state in an upper or lower branch of one phase breaker and in a lower or upper branch of either another phase breaker or two other phase breakers at a time. [5] Direct current (DC) power distribution arrangement method according to claim 3 or 4, characterized by that the inverter units (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) keep the selected controllable circuit breakers in an on state, either: continuously; or for a predefined duration, in which case the on-state periods of the selected controllable circuit breakers are rotated such that the average load of each AC terminal (U, V, W) of the inverter unit (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) is essentially the same. [6] Direct current (DC) power distribution arrangement method according to one of the preceding claims 4-5, characterized by , that a DC power distribution subsystem (DC1) is externally charged to the normal operating voltage level, and the upper level control the inverter unit (INU) connected to the fully charged subsystem (DC1) 41 , INU 42 , INU 43 , INU44, INU 45 ) in such a way that its pulse-width modulated output voltage rises to full level at a predefined speed. [7] Direct current (DC) power distribution arrangement method according to one of the preceding claims 4-6, characterized by , that the controllable circuit breakers of at least one inverter unit (INU 41 , INU 42 , INU 43 , INU44, INU 45 ) in the system are kept off while at least two connecting links (D, E, F, G, H) are energized.

Images