KR102115787B1 - Dc shipboard power system - Google Patents

Abstract

According to an embodiment of the present invention, there is provided a DC linear power system capable of ensuring protection sensitivity and selective blocking.
The DC linear power system according to an embodiment of the present invention is connected between a plurality of power supply units each having a DC bus (DC BUS) that converts power from a generator and supplies it to a load, and is connected between the DC buses of the plurality of power supply units. Bus tie breaker (BUS TIE BREAKER) that electrically connects or disconnects a plurality of power supply units and an energy supply unit that is connected between the DC buses of the plurality of power supply units to supply capacitive energy to a failed power supply unit among the plurality of power supply units It can contain.

Description

DC SHIPBOARD POWER SYSTEM

The present invention relates to a DC linear power system.

In general, ships are equipped with diesel electric power supply for propellers and thrusters. Electrical energy is produced on board the vessel by a power plant equipped with a diesel engine and/or a generator driven by a gas turbine, and a marine automation system including a Power Management System (PMS).

2. Description of the Related Art In recent years, the application of a DC-line power system has increased to save energy on ships. In addition, a thruster driven by a power conversion device has been widely used to improve ship control.

In particular, when a thruster, for example, a thruster is simultaneously applied in a ship to which direct current is applied, the speed of the thruster is controlled by configuring each feeder in the control panel.

In the DC line power system, when a failure occurs in the DC ship load feeder, the fuse is melted to eliminate the failure. The magnitude or energy of the failure may differ greatly depending on the ship operation mode or the location of the failure, and the protection sensitivity of the fuse And blocking selection can be difficult to satisfy all.

That is, for the same fault feeder accident, a difference in the magnitude and energy of the fault current occurs depending on the operation mode. For example, in operation mode 1, the magnitude and energy of the fault current in the healthy feeder is greater than the fault feeder in the operation mode 3, and the protection sensitivity is higher. And difficulty in blocking selection may occur.

Republic of Korea Patent No. 10-2017-0104578

According to an embodiment of the present invention, there is provided a DC linear power system capable of ensuring protection sensitivity and selective blocking.

In order to solve the problems of the present invention described above, the DC linear power system according to an embodiment of the present invention includes a plurality of power supply units each having a DC bus (DC BUS) that converts power from a generator and supplies it to a load. Bus tie breaker (BUS TIE BREAKER) which is connected between the DC bus lines of a plurality of power supply units and electrically connects or cuts off the plurality of power supply units, and is connected between the DC bus lines of the plurality of power supply units, and the failed power among the plurality of power supply units The supply unit may include an energy supply unit that supplies capacitive energy.

According to an embodiment of the present invention, it is possible to prevent the voltage drop of the healthy bus for one bus accident to improve the protection stability and to protect the sensitivity and selectivity.

1 is a schematic configuration diagram of a DC linear power system according to an embodiment of the present invention.
2A to 2C are diagrams of a DC linear power system according to an embodiment of the present invention.
3A and 3B are graphs of a prospective current according to a capacity of a bus capacitor of a DC linear power system according to an embodiment of the present invention.
4A to 4F are diagrams showing an effective current graph and current flow of a DC linear power system according to an embodiment of the present invention.

Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily implement the present invention.

1 is a schematic configuration diagram of a DC linear power system according to an embodiment of the present invention.

Referring to FIG. 1, the DC linear power system 100 according to an embodiment of the present invention includes a plurality of power supply units 110 and 120, a bus tie breaker 130 and an energy supply unit 140 can do.

The plurality of power supply units 110 and 120 may include at least a first power supply unit 110 and a second power supply unit 120.

Each of the first and second power supply units 110 and 120 includes a converter unit 111 and 121 and an inverter unit 113 and 123, and a DC busbar 112 and 122 that delivers DC power from the converter units 111 and 121 to the inverter units 113 and 123. can do.

The converter units 111 and 121 may include a plurality of converters that convert AC power from the generator G into DC power, and the inverter units 113 and 123 convert DC power from the DC bus lines 112 and 122 into AC power. It may include a plurality of inverters.

Fuse parts 114 and 124 may be disposed between the DC bus lines 112 and 122 and the inverter parts 113 and 123.

The fuse units 114 and 124 may include a plurality of fuses disposed between the DC buses 112 and 122 and each of the plurality of inverters of the inverter units 113 and 123, and the plurality of fuses may provide a power transmission path when power transmission of the corresponding path is abnormal. Can be blocked.

As described above, in the DC line power system, when a failure occurs in the DC ship load feeder, the fuse is melted to eliminate the failure. The magnitude or energy of the failure may vary depending on the ship operation mode or the location of the failure. It can be difficult to satisfy both the fuse's protective sensitivity and selective disconnection.

That is, for the same fault feeder accident, a difference in the magnitude and energy of the fault current occurs depending on the operation mode. For example, in operation mode 1, the magnitude and energy of the fault current in the healthy feeder is greater than the fault feeder in the operation mode 3, and the protection sensitivity is higher. And difficulty in blocking selection may occur.

Accordingly, the DC linear power system of the present invention includes an energy providing unit 140.

The energy providing unit 140 may include a plurality of capacitors C1 and C2, and, for example, when the first and second power supply units 110 and 120 are formed, one end side of the first DC bus 112 A first capacitor C1 may be disposed at a pole-to-pole, and one end pole adjacent to one end of the first DC bus 112 among the short sides of the second DC bus 124- A second capacitor C2 may be disposed on the two-pole.

The energy supply unit 140 may supply capacitive energy to a failed power supply unit among a plurality of power supply units. For example, the fuse unit 124 in the second power supply unit 120 may include first to third fuses. If the first to third fuse is connected to one of the load (thruster, large-capacity motor, hotel load) of the power transmission path (feeder), the fuse is melted when an excessive current flows in the power transmission path Energy may be provided to cut off the power transmission path.

When the accident current reaches the threshold, the bus tie breaker 130 quickly interrupts the accident current, and then the voltage of the normal bus rises again. Standard. That is, the maximum voltage drop of a normal bus must be higher than the converter's low voltage trip during the Fault Clearing Time.

In the DC line power system, the inductance between a failed configuration and a normal configuration plays an important role in alleviating the voltage drop of a normal bus due to the opposite characteristic of a rapid current change. Without this inductance, all DC busbars can suffer huge voltage drops due to DC failures and can isolate all electrical sources and loads from the bus. The initial current of the DC fault is mainly contributed by a capacitor installed in the DC pole-to-pole. This is because capacitors respond much faster than alternators.

2A is a graph for analyzing the sensitivity of the residual voltage of a DC capacitor according to values of a capacitor and an inductor. That is, it can be seen that the higher the value of the capacitance, the less the dynamic coupling between the two buses, thereby reducing the voltage drop of the DC capacitor. DC inductance has more effect on voltage drop than DC capacity.

Here, OM1, OM2, and OM3 are each operating mode, OM1 is dynamic placement (maximum load condition), OM2 is port entry/exit (medium load condition), and OM3 can mean navigation (minimum load condition) operation mode. have.

2B is a graph of a result of performing voltage drop analysis for each system, and FIG. 2C is a graph of a minimum inductance required for the system.

The difference between centralized and decentralized systems comes from how to connect generators and rectifiers, rectifiers and other equipment such as DC busbars, DC busbar-inverters and inverter loads. A centralized system can connect an alternator rectifier and an inverter load using an AC cable, and a distributed system can connect a DC bus, an inverter, and a converter using a DC cable.

As mentioned earlier, a specific value of the system inductance is necessary to maintain the bus voltage in a normal configuration. The distributed system (T3) has a much higher inductance than the centralized system (T1) due to the direct current cable. Circuit conditions, such as operating mode and fault location, also have a large impact on the voltage drop.

It is observed that the centralized system T1 has a higher voltage drop in all modes of operation than the distributed system T3. Failure of the thruster motor feeder (FTM) during the operation mode indicates the maximum voltage drop of the centralized system (T1), the distributed system (T3), the centralized system with bus capacitors (T2) and the distributed system (T4). .

Installing an additional 100 mF bus capacitor on the bus improves the residual voltages (T2 and T4) of the centralized and decentralized systems compared to the centralized and distributed systems (T1 and T3) without bus capacitors.

Referring to FIG. 2C, the port entry/exit mode (OM2) in which the failure occurred in the thruster motor feeder (F TM) is the worst case, and the minimum inductance required for each system under this condition can be seen. In order to maintain a voltage of 0.8pu (converter low voltage condition) at 1ms after a failure, a system inductance of 3~30μH is required depending on the system topology. Since the system inductance is small in a centralized system, an additional inductance must be installed in the center of the bus tie breaker. Alternatively, a bus capacitor may be installed to minimize the inductance value. In general, a high system inductance can cause instability problems depending on the system state and converter type, while a high system capacitance improves system stability. Therefore, the system stability can be increased by including the energy supply unit 140 in the DC linear power system.

After bus protection (after opening the bus tie breaker), the high-speed fuse (or semiconductor fuse) melts the device within hundreds of microseconds to isolate the faulty feeder. In a DC-line power system, system capacitance is the main energy source that blows the fuse and its value is related to the total clearing time of the fuse. The total clearing time is the total time taken to clear the fault with the fuse.

3A and 3B are graphs of a prospective current according to a capacity of a bus capacitor of a DC linear power system according to an embodiment of the present invention.

3A is an effective current graph according to the capacity of a bus capacitor of a centralized system among DC linear power systems according to an embodiment of the present invention, and FIG. 3B is a DC linear power system according to an embodiment of the present invention. It is a graph of the effective current according to the capacity of the bus capacitor in a distributed system.

The centralized system (T1) shows a faster fault clearing time than the distributed system (T3) for the same fault in Figure 7.

The total clear time for "C = 100%" is about 0.45 to 0.65 ms for the centralized system (T1) and about 1.5 to 2.0 ms of the distributed system (T3) for the selected fuses (fuses 1, 2 and 3). . For the distributed system (T3), the time adjustment between feeder protection (secondary protection) and generator-rectifier failure control (third protection) is difficult to implement using these total clearing times.

The time margin between the two protections necessary to increase the protection reliability is not sufficient considering the generator-rectifier fault control (3rd protection) operating time and the fault tolerance of the semiconductor device. In addition, it can be seen that both systems (T1 and T3) have high capacitance values ("C = 200%") that increase the magnitude and energy of the fault current. However, DC linear power systems with high capacitance ("C = 200 %") have a slow effective current rise characteristic and provide a delayed fault clearing time compared to low capacitance ("C = 50 %").

There are two important technical aspects to system protection: selectivity and sensitivity. Selectivity means that the fuse connected to the faulty feeder must eliminate the fault without pre-arcing the fuse connected to the other feeder. On the other hand, the sensitivity means that the fuse of the defective feeder must eliminate the fault for the minimum fault energy condition as well as the maximum fault energy condition. In order to protect the system with a fuse, it must be designed with this aspect in mind.

4A to 4F are diagrams showing an effective current graph and current flow of a DC linear power system according to an embodiment of the present invention.

4A and 4B, in the case of the centralized system T1, the second fuse and the third fuse are fuses of a faulty feeder (LM feeder) (fault feeder) and fuses of a normal feeder (TM feeder) (normal Provides selectivity between the feeder and the same fuse/current rating). On the other hand, due to the small fault current and fault energy of the navigation mode OM3, it is not possible to select a fuse that satisfies both the dynamic placement mode OM1 and the navigation mode OM3. That is, sensitivity cannot be achieved. This sensitivity problem is also observed in the dispersion system T3 of Fig. 4c. The sensitivity problem is due to the fact that the fault energy passing through the fuse of the TM feeder is only provided by the capacitor of the hotel load (CHL) in voyage mode (OM3). Fault energy is not sufficient to blow fuses applied to large motor peters because the value of the selected hotel load (CHL) is much less than that of a large capacity motor (CLM).

In centralized and decentralized systems with bus capacitors (T2 and T4), a bus capacitor of 100 mF directly contributes to the additional fault energy through the fuse feeder's fuse under fault conditions, as shown in Figures 4c and 4f. Also, by comparing the centralized and decentralized systems with bus capacitors (T2 and T4) and the centralized and decentralized systems (T1 and T3), the current through which the bus capacitor passes through the fuses of the normal feeder (TM feeder). It is observed that it decreases the ascent rate and the maximum value of. That is, using a bus capacitor can solve the sensitivity problem.

In Fig. 4c, for a centralized system T2 with a bus capacitor, the first fuse and the second fuse can be used to achieve selectivity between a failed feeder (LM feeder) and a normal feeder (TM feeder). have. For the third fuse, the time between the total clearing time of the faulty feeder (LM feeder) for the dynamic placement mode (OM1) and the pre-arcing time of the normal feeder (TM feeder) for the dynamic placement mode (OM1). There is no margin.

The advantage of additional bus capacitance is even more important in a distributed system (T4) with bus capacitors.

As shown in Fig. 4f, the magnitude of the fault current of the normal feeder (TM feeder) is clearly smaller than the fault current of the faulty feeder (LM feeder) for the dynamic placement mode OM1 and the navigation mode OM3. This is a decentralized system with a bus capacitor (T4) when a fuse with a value higher than the actual bus capacitor's capacity value or a lower rating than the first fuse is applied to the decentralized system (T4) with the bus capacitor. ), which means faster fault clearing is possible.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, but is limited by the claims, which will be described later, and the configuration of the present invention can be varied within the scope of the technical spirit of the present invention. Those of ordinary skill in the art to which the present invention pertains can readily appreciate that such changes and modifications can be made.

100: DC linear power system.
110: first power supply
111,121: converter unit
112: first DC bus
113, 123: inverter unit
114, 124: fuse unit
120: second power supply
122: second DC bus
130: bus tie breaker
140: energy provider
C1: first capacitor
C2: Second capacitor

Claims (5)

A plurality of power supply units each having a DC bus that converts power from the generator and supplies it to the load
A bus tie breaker connected between the DC bus lines of the plurality of power supply units to electrically connect or cut off the plurality of power supply units (BUS TIE BREAKER); And
And an energy supply unit connected between the DC bus lines of the plurality of power supply units to supply capacitive energy to the failed power supply unit among the plurality of power supply units,
The plurality of power supply units include a first power supply unit and a second power supply unit,
The energy supply unit is arranged in parallel with the bus tie breaker between the DC buses,
The energy supply unit includes a first capacitor disposed between the DC bus line and the ground of the first power supply, and a second capacitor disposed between the DC bus line and the ground of the second power supply, and disposed adjacent to the first capacitor. ,
In the first capacitor, when at least one of loads of a power transmission path to which the fuse of the first power supply is connected operates, and an excessive current flows in the power transmission path, energy is supplied to the corresponding fuse to cut off the power transmission path. The second capacitor is DC line power to provide energy to the fuse to cut off the power transmission path when at least one of the loads of the power transmission path to which the fuse of the second power supply is connected operates, and an excessive current flows in the power transmission path. system.
According to claim 1,
Each of the plurality of power supply unit
A converter unit having a plurality of converters that convert AC power from the generator into DC power;
An inverter unit having a plurality of inverters for converting the DC power from the DC bus to transfer DC power from the converter unit into AC power; And
Fuse unit having a plurality of fuses (Fuse) disposed between each of the DC bus and the plurality of inverters
DC line power system comprising a.
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