KR20240178411A - Converter for low voltage direct current power system and controlling method thereof - Google Patents

Abstract

A converter for a low-voltage DC system and a control method thereof are disclosed. A converter for a low-voltage DC system according to one aspect of the present invention is characterized by including a switching unit that converts three-phase AC power into DC power, a smoothing capacitor to which the DC power converted by the switching unit is applied, a high-voltage diode connected in series with the smoothing capacitor, a switching element connected in parallel with the high-voltage diode, and a freewheeling diode connected in parallel with the switching element.

Description

CONVERTER FOR LOW VOLTAGE DIRECT CURRENT POWER SYSTEM AND CONTROLLING METHOD THEREOF

The present invention relates to a converter for a low-voltage direct current system and a control method thereof, and more particularly, to a converter applied to a low-voltage direct current system and a control method thereof.

The converter can convert the input AC power into DC power and output it. Meanwhile, if a ground fault or line-to-line short circuit occurs in the DC system connected to the converter, a surge of tens to hundreds of kA may occur depending on the capacity and time constant of the smoothing capacitor. In general, this surge lasts for a short time (tens of us), but depending on the line impedance and fault resistance, it may last for a considerably long time (tens of ms). This surge can cause transient phenomena such as lightning impulses to semiconductor elements, system equipment, and customer equipment, thereby damaging various equipment connected to the system.

The background technology of the present invention is disclosed in Korean Patent Publication No. 10-2018-0067207 (June 20, 2018).

An object of one aspect of the present invention is to provide a converter for a low-voltage DC system and a control method thereof capable of preventing a surge from occurring by a smoothing capacitor included in the converter in a system fault situation (ground fault or short circuit).

A low-voltage DC system converter according to one aspect of the present invention is characterized by including: a switching unit that converts three-phase AC power into DC power; a smoothing capacitor to which the DC power converted by the switching unit is applied; a high-voltage diode connected in series with the smoothing capacitor; a switching element connected in parallel with the high-voltage diode; and a freewheeling diode connected in parallel with the switching element.

The present invention further includes a processor for controlling the switching unit and the switching element, and is characterized in that the processor turns on the switching element to prevent a surge from occurring by the smoothing capacitor when a fault occurs in the system.

The present invention further includes a current sensor for detecting a fault current of the system, and the processor is characterized in that it determines that a fault has occurred in the system when the fault current detected through the current sensor is equal to or higher than a preset reference current.

In the present invention, the processor is characterized in that it performs an FRT (Fault Ride Through) function by controlling the switching unit when a failure occurs in the system.

In the present invention, the processor is characterized in that, when no failure occurs in the system, the switching element is opened to charge the smoothing capacitor through the high-voltage diode or to discharge the smoothing capacitor through the freewheeling diode.

According to one aspect of the present invention, a control method for a low-voltage DC system converter comprises a switching unit which converts three-phase AC power into DC power, a smoothing capacitor to which the DC power converted by the switching unit is applied, a high-voltage diode connected in series with the smoothing capacitor, a switching element connected in parallel with the high-voltage diode, a freewheeling diode connected in parallel with the switching element, and a processor which controls the switching unit and the switching element, characterized in that the control method comprises a step of the processor determining whether a fault has occurred in the system; and a step of the processor turning on the switching element to prevent a surge from occurring by the smoothing capacitor when a fault has occurred in the system.

According to one aspect of the present invention, the present invention can prevent a surge from occurring by a smoothing capacitor by quickly disconnecting the smoothing capacitor of a converter when a fault occurs in a system.

According to another aspect of the present invention, the present invention can eliminate the need to operate a circuit breaker at ultra-high speed to prevent surges by configuring a converter to prevent surges from occurring by a smoothing capacitor, thereby inducing simplification of circuit breakers applied to low voltage DC systems and eliminating the need to connect a series reactor to a low voltage DC system to reduce the maximum fault current.

Meanwhile, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

FIG. 1 is a block diagram showing a converter for a low-voltage direct current system according to one embodiment of the present invention.
FIG. 2 is a circuit diagram showing a converter for a low-voltage direct current system according to one embodiment of the present invention.
FIG. 3 is a flowchart showing a control method of a converter for a low-voltage direct current system according to one embodiment of the present invention.
Figure 4 is an exemplary diagram showing the result of applying a converter for a low-voltage direct current system according to one embodiment of the present invention to a system.

Hereinafter, a low-voltage DC system converter and a control method thereof according to an embodiment of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of lines and the size of components illustrated in the drawings may be exaggerated for the sake of clarity and convenience of explanation. In addition, the terms described below are terms defined in consideration of functions in the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, the definitions of these terms should be made based on the contents throughout this specification.

FIG. 1 is a block diagram showing a converter for a low-voltage direct current system according to one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a converter for a low-voltage direct current system according to one embodiment of the present invention.

Referring to FIGS. 1 and 2, a low-voltage direct current system converter according to one embodiment of the present invention may include a switching unit (10), a smoothing capacitor (20), a high-voltage diode (30), a switching element (40), a freewheeling diode (50), a current sensor (60), a memory (70), and a processor (80). A low-voltage direct current system converter according to one embodiment of the present invention may further include various components in addition to the components illustrated in FIGS. 1 and 2, or may omit some of the components among the above components.

The switching unit (10) can convert three-phase AC power into DC power and output it. The switching unit (10) can include a plurality of switching elements. The switching elements included in the switching unit (10) can be, but are not limited to, an insulated gate bipolar mode transistor (IGBT), a gate turn off thyristor (GTO), or a field effect transistor (FET).

The smoothing capacitor (20) can smooth and output the DC power output from the switching unit (10). The DC power converted from the switching unit (10) can be applied to the smoothing capacitor (20), and the smoothing capacitor (20) can remove high-frequency noise included in the DC power.

A high voltage diode (30) can be connected in series with a smoothing capacitor (20). The high voltage diode (30) can control the direction of current so that the direct current power output from the switching unit (10) is applied to the smoothing capacitor (20).

The switching element (40) can be connected in parallel to the high voltage diode (30). The switching element (40) can suppress the energy charged in the smoothing capacitor (20) from being discharged in a situation where a fault occurs in the system. The switching element (40) can be an insulated gate bipolar mode transistor (IGBT), a gate turn off thyristor (GTO), or a field effect transistor (FET), but is not limited thereto.

A freewheeling diode (50) can be connected in parallel to the switching element (40). The freewheeling diode (50) can control the direction of current so that the smoothing capacitor (20) is discharged.

The current sensor (60) can detect a fault current in a system (DC system) to which the converter is connected. The fault current detected through the current sensor (60) can be used to determine whether a fault has occurred in the system to which the converter is connected.

The memory (70) may store various information required during the operation of the processor (80). In addition, the memory (70) may store various information produced during the operation of the processor (80).

The processor (80) may be operatively connected to the switching unit (10), the switching element (40), the current sensor (60), and the memory (70). The processor (80) may also be implemented as a central processing unit (CPU), a micro controller unit (MCU), or a system on chip (SoC), and may control a plurality of hardware or software components connected to the processor (80) by driving an operating system or an application, perform various data processing and calculations, and may be configured to execute at least one command stored in the memory (70) and store the execution result data in the memory (70).

The processor (80) can control the switching of the switching elements included in the switching unit (10) so that the three-phase AC power can be converted into DC power by the switching unit (10). The processor (80) can control the switching of the switching elements included in the switching unit (10) through PWM control. The processor (80) can determine whether a fault has occurred in the system to which the converter is connected based on the fault current detected through the current sensor (60).

The processor (80) can open the switching element (40) when no failure occurs in the system. That is, the processor (80) can enable the smoothing capacitor (20) to be charged and discharged normally by opening the switching element (40) in a normal situation where no failure occurs in the system.

The processor (80) can insert the switching element (40) to prevent a surge caused by the smoothing capacitor (20) when a fault occurs in the system. The processor (80) can prevent a surge from occurring by the smoothing capacitor (20) by switching the state of the switching element (40) to ON when a fault occurs in the system. The processor (80) can control the switching unit (10) to perform an FRT (Fault Ride Through) function when a fault occurs in the system. That is, the processor (80) can control the switching unit (10) so that the switching unit (10) continues to operate even when a fault occurs in the system. A method for performing the FRT function can be known to those skilled in the art to which the present invention pertains, and thus a detailed description thereof will be omitted.

FIG. 3 is a flowchart showing a control method of a converter for a low-voltage direct current system according to one embodiment of the present invention.

Hereinafter, a control method of a converter for a low-voltage direct current system will be described with reference to Fig. 3. Some of the processes described below may be performed in a different order from the order described below or may be omitted.

First, the processor (80) can determine whether a fault has occurred in the system (S301). In step S301, the processor (80) can determine whether a fault (e.g., a short circuit or a ground fault) has occurred in the system based on the fault current detected by the current sensor (60). In step S301, the processor (80) can determine that a fault has occurred in the system if the fault current detected by the current sensor (60) is greater than or equal to a preset reference current.

If no fault occurs in the system, the processor (80) can open the switching element (40) (S303). That is, in a normal situation where no fault occurs in the system, the processor (80) can open the switching element (40) to allow the smoothing capacitor (20) to be normally charged and discharged. In step S303, the smoothing capacitor (20) can be charged through the current flowing through the high-voltage diode (30). In step S303, the electric energy stored in the smoothing capacitor (20) can be discharged through the freewheeling diode (50). In step S303, the processor (80) can control the switching of the switching elements included in the switching unit (10) so that the three-phase AC power can be converted into DC power by the switching unit (10).

In the event of a fault in the system, the processor (80) can turn on the switching element (40) (S305). That is, in a situation where a fault occurs in the system, the processor (80) can prevent a surge from occurring by the smoothing capacitor (20) by turning on the switching element (40). In step S305, the smoothing capacitor (20) can be charged through the current flowing through the high-voltage diode (30), but the electric energy stored in the smoothing capacitor (20) cannot be discharged through the freewheeling diode (50). In this way, the present invention can prevent a surge from occurring by the smoothing capacitor (20) by quickly disconnecting the smoothing capacitor (20) of the converter when a fault occurs in the system, thereby suppressing the electric energy stored in the smoothing capacitor (20) from being discharged.

Next, the processor (80) can control the switching unit (10) to perform the FRT (Fault Ride Through) function (S307). That is, the processor (80) can control the switching unit (10) so that the switching unit (10) continues to operate.

Meanwhile, in the above-described embodiment, the operation of controlling the switching unit (10) to perform the FRT function is described as being performed after the operation of turning on the switching element (40), but the operation of performing the FRT function may be performed before the operation of turning on the switching element (40), or may be performed simultaneously with the operation of turning on the switching element (40).

Afterwards, the circuit breakers connected to the system may operate to isolate the faulted section, thereby restoring the system voltage and system current to normal.

Figure 4 is an exemplary diagram showing the result of applying a converter for a low-voltage direct current system according to one embodiment of the present invention to a system.

As shown in Fig. 4, when a fault occurs in the system to which the converter is connected, and the smoothing capacitor (20) is immediately disconnected by inserting a switching element (40), it can be confirmed that the discharge of electric energy charged in the smoothing capacitor (20) is suppressed, and a fault current according to the fault point impedance occurs without a surge.

As described above, the converter for a low-voltage DC system and the control method thereof according to an embodiment of the present invention can prevent a surge from occurring by a smoothing capacitor by quickly disconnecting the smoothing capacitor of the converter when a fault occurs in the system. In addition, the converter for a low-voltage DC system and the control method thereof according to an embodiment of the present invention can eliminate the need to operate a circuit breaker at ultra-high speed to prevent a surge by configuring the converter to prevent a surge from occurring by the smoothing capacitor, thereby inducing simplification of a circuit breaker applied to a low-voltage DC system and eliminating the need to connect a series reactor to a low-voltage DC system to reduce the maximum fault current.

The implementations described herein may be implemented, for example, as a method or process, an apparatus, a software program, a data stream or a signal. Even if discussed in the context of only a single form of implementation (e.g., discussed only as a method), the implementation of the discussed features may also be implemented in other forms (e.g., as an apparatus or a program). The apparatus may be implemented using suitable hardware, software, firmware, and the like. The method may be implemented in an apparatus such as a processor, which generally refers to a processing device including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. A processor also includes a communication device such as a computer, a cell phone, a personal digital assistant ("PDA"), and other devices that facilitate communication of information between end-users.

Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Accordingly, the true technical protection scope of the present invention should be determined by the following patent claims.

10: Switching section
20: Smoothing capacitor
30: High voltage diode
40: Switching element
50: Freewheeling diode
60: Current sensor
70: Memory
80: Processor

Claims (9)

A switching unit that converts three-phase AC power into DC power;
A smoothing capacitor to which the DC power converted in the above switching unit is applied;
A high voltage diode connected in series with the above smoothing capacitor;
A switching element connected in parallel to the high voltage diode; and
A converter for a low-voltage direct current system, characterized by including a freewheeling diode connected in parallel to the above switching element.
In paragraph 1,
Further comprising a processor for controlling the switching unit and switching element,
The above processor is a low-voltage direct current system converter characterized in that it inserts the switching element to prevent a surge from occurring by the smoothing capacitor when a fault occurs in the system.
In the second paragraph,
Further comprising a current sensor for detecting a fault current of the above system,
A converter for a low-voltage direct current system, characterized in that the processor determines that a fault has occurred in the system when the fault current detected through the current sensor is greater than a preset reference current.
In the second paragraph,
A low-voltage direct current system converter, characterized in that the processor controls the switching unit to perform an FRT (Fault Ride Through) function when a fault occurs in the system.
In the second paragraph,
A converter for a low-voltage direct current system, characterized in that the processor opens the switching element to charge the smoothing capacitor through the high-voltage diode or to discharge the smoothing capacitor through the freewheeling diode when no failure occurs in the system.
A control method for a converter for a low-voltage DC system, comprising: a switching unit that converts three-phase AC power into DC power; a smoothing capacitor to which the DC power converted by the switching unit is applied; a high-voltage diode connected in series with the smoothing capacitor; a switching element connected in parallel with the high-voltage diode; a freewheeling diode connected in parallel with the switching element; and a processor that controls the switching unit and the switching element.
The step of the above processor determining whether a failure has occurred in the system; and
A control method for a converter for a low-voltage direct current system, characterized in that the processor includes a step of turning on the switching element to prevent a surge from occurring by the smoothing capacitor when a failure occurs in the system.
In paragraph 6,
A control method for a converter for a low-voltage direct current system, characterized in that the processor determines that a fault has occurred in the system when the fault current of the system is greater than a preset reference current.
In paragraph 6,
A control method for a converter for a low-voltage direct current system, characterized in that the processor further includes a step of controlling the switching unit to perform an FRT (Fault Ride Through) function when a fault occurs in the system.
In paragraph 6,
A control method for a converter for a low-voltage direct current system, characterized in that the processor further includes a step of opening the switching element to charge the smoothing capacitor through the high-voltage diode or to discharge the smoothing capacitor through the freewheeling diode when no failure occurs in the system.

Images