KR20160080018A - Power control device for sub-module of mmc converter - Google Patents

Abstract

The present invention relates to a power control device for a sub module of a modular multi-level converter (MMC) capable of controlling power supply to the sub module of the MMC linked to a high-voltage direct-current (HVDC) power transmission system and a static compensator (STATCOM). According to the present invention, the power control device includes: at least one first resistor which is connected between the P and N bus bars of the MMC; a second resistor which is serially connected to the first resistor; a switch which is serially connected to the second resistor; a third resistor which is connected in parallel to the serial connection of the second resistor and the switch; a zener diode which is connected in parallel to the third resistor; and a DC/DC converter which is connected to the output terminals of the two ends of the zener diode, converts the voltage between the two terminals of the zener diode, and delivers the converted voltage to the sub module. Depending on the on/off switching of the switch, the amount of current flowing to the zener diode is controlled.

Description

POWER CONTROL DEVICE FOR SUB-MODULE OF MMC CONVERTER FOR MMC CONVERTER

[0001] The present invention relates to a power supply control device, and more particularly to a power supply control device which is equipped with a stable power supply (not shown) in a sub-module of a modular multilevel converter (MMC) connected to a high voltage direct current transmission (HVDC) system and a static type synchronous compensator Power supply control device for a submodule of an MMC converter for controlling supply of power.

Generally, in an HVDC (High Voltage Direct Current) system, AC power generated by a power plant is converted into DC power, and the power is supplied to the load by reconverting the power from AC power to AC power. This HVDC system has advantages such as efficient and economical power transmission through voltage boosting, heterogeneous grid connection, and long distance high efficiency transmission. STATCOM (Static Synchronous Compensator) is one of the FACTS (Flexible AC Transmission System) devices, which is connected to the power system to increase the power transmission capacity and to maximize the utilization rate of existing facilities. Means the compensating device of This STATCOM system has the advantage of stabilizing the system by keeping the voltage constant by compensating the system in parallel by using the voltage type power semiconductor.

An MMC converter can be connected to the HVDC system or STATCOM. In this MMC converter, a plurality of sub-modules are connected in series. In MMC converters, submodules are a very important component. Therefore, it is required to supply stable power to the sub-module in order to allow the sub-module to operate normally in various environments. Also, in the MMC converter, the submodule converts the voltage and becomes the path of current for power transmission. Since the loss occurring in the operation of such a sub-module adversely affects the efficient operation of the sub-module, efforts are being made to minimize it.

FIG. 1 is an equivalent circuit diagram of an MMC converter, and FIG. 2 is a circuit diagram of a power control device for a submodule of a conventional MMC converter. As is well known, the MMC converter is composed of one or more phase modules 1, and each phase module 1 has a plurality of submodules 10 connected in series. Each phase module 1 connects the DC voltage side to the positive and negative DC voltage bus lines P and N, respectively. A DC voltage of high voltage exists between these DC voltage P-N bus lines. Each sub module 10 is formed with two connection terminals X1 and X2.

Conventionally, the power supply controller 20 for a submodule of an MMC converter converts a high voltage (about 2 to 3 kV) of a P-N bus line to a low voltage (about 300 to 400 V) to supply power necessary for operation of the submodule. At this time, due to the characteristics of the HVDC system, a combination of a resistor (R) and a zener diode (Z) is used to maintain high reliability. For example, the current is limited by using specific resistors R1 and R2 among a plurality of resistors R1 to R3 connected in series between the P-N bus lines, and the voltage is converted to a low voltage by using the Zener diode Z.

However, such a conventional power supply control apparatus 20 has a problem in that a loss due to heat generation occurs in the resistors R1 and R2 for current limitation, and this heat generation is closely related to the reliability of the device, The operation may be adversely affected. Therefore, it is troublesome to install a heat sink for preventing heat generation.

In addition, the submodule of the MMC converter associated with the HVDC system accommodates a very wide input voltage range (0 to 3 kV), and since the MMC converter must be operated in combination with it, Should all be supplied normally. For this reason, if the current limiting resistors (R1, R2) are selected so that the output of the control power supply can be normally performed in the 800V region and if the input voltage is increased to 3 kV, a large current flows through the resistors R1 and R2, And cause heat generation.

At the same time, most of the increased current flows into the zener diode (Z), causing a high heat generation of the control diode (Z), which greatly affects the reliability. This is because the resistance value of the Zener diode (Z) is generally smaller than the line resistance value of R3.

In the case of the current limiting resistors R1 and R2, the heat dissipation can be smoothly performed by using the heat dissipation plate. However, in the case of the Zener diode Z, there is a problem that mounting of a heat dissipation plate or the like is difficult due to volume expansion or the like.

Therefore, in the related art, there is a demand for development of a power control device that enables stable power control while minimizing loss in a current limiting resistor without installing additional devices in a submodule of an MMC converter associated with an HVDC system.

The present invention relates to a power control device for a submodule of an MMC converter that converts a high voltage to a low voltage in an HMC system and an MMC converter associated with a STATCOM to supply heat to the MMC converter submodule The purpose is to provide.

Another object of the present invention is to provide a power control device for a submodule of an MMC converter that minimizes burden on a zener diode in accordance with an on / off switching operation of a switch element serially connected to a current limiting resistor.

A power supply control device for a submodule of an MMC converter according to the present invention includes:

At least one first resistor connected between the P-N buses of the MMC converter; A second resistor serially connected to the first resistor; A switch serially connected to the second resistor; A third resistor coupled in parallel to the series connection of the second resistor and the switch; A zener diode connected in parallel to the third resistor; And a DC / DC converter connected to output terminals of both ends of the zener diode for converting a voltage between both ends of the zener diode and delivering the voltage to the submodule. And controls the magnitude of the current flowing to the Zener diode in accordance with on / off switching of the switch.

In the present invention, the resistance value of the third resistor is larger than the resistance value of the second resistor.

In the present invention, the voltage between the P-N bus lines increases or decreases in the range of 0 to a predetermined maximum voltage (Vmax).

In the present invention, when the voltage between the P-N bus lines is in the range of 0 V to the first voltage, the switch is turned off so that no current flows to the second resistor.

In the present invention, when the voltage between the P-N bus lines is in the range of the first voltage to the maximum voltage, the switch is turned on so that current flows to the second resistor.

In the present invention, the first voltage is determined according to the magnitude of the current flowing to the Zener diode.

In the present invention, the apparatus further includes a current detector for detecting a current flowing in the Zener diode. In a state where the switch is initially turned off, the voltage between the PN bus lines is increased from 0 to a predetermined maximum voltage Vmax And alternately turns on / off the switch according to a current value of the Zener diode detected by the current detector to repeatedly supply / cut off the current to the second resistor.

In the present invention, the duty ratio of on / off switching of the switch is varied so that the current flowing to the Zener diode is kept below a preset reference value.

According to the present invention, it is possible to minimize the loss occurring in various devices inside the power control device for the submodule of the MMC converter, and to prevent the heat generation, there is no need to install a separate device such as a heat sink of the Zener diode.

In addition, according to the present invention, the burden of the zener diode used in the power supply control device can be reduced, so that the size of the zener diode can be reduced to the utmost, which enables downsizing and weight reduction.

1 is an equivalent circuit diagram of a general MMC converter,
2 is a circuit diagram of a power supply control device for a submodule of a conventional MMC converter,
3 is a circuit diagram of a power supply control device for a submodule of an MMC converter according to an embodiment of the present invention,
4 is a schematic diagram of a current flow for explaining a power control process of a submodule in a power control apparatus for a submodule of an MMC converter according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals whenever possible, even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the difference that the embodiments of the present invention are not conclusive.

In describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected or connected to the other component, Quot; may be "connected," "coupled," or "connected. &Quot;

3 is a circuit diagram of a power control device for a submodule of an MMC converter according to an embodiment of the present invention.

Referring to FIG. 3, the power supply control apparatus 100 for a submodule of an MMC converter according to an exemplary embodiment of the present invention includes an MMC converter including one or more phase modules, a plurality of submodules To supply power to operate. To this end, the power supply control apparatus 100 according to the present invention converts a high voltage between a positive (+) and a negative (-) P bus line connected to each phase module and a N bus line into a low voltage necessary for operation of the sub- . These MMC converters are linked to the HVDC system and the STATCOM.

The power supply control apparatus 100 of the present invention includes at least one first resistor R4 110 connected between the PN bus lines of the MMC converter and a second resistor R5 120 connected in series to the first resistor R4 110 . The first resistor 110 is connected in series with one or more resistors. A switch 130 is connected in series to the second resistor 120. The switch 130 may be variously implemented as a mechanical switch, a relay contact switch, or a semiconductor switch device. IGBTs, FETs, and the like may be used as the semiconductor switch elements, and reverse diodes for limiting current flow are preferably connected in series when a mechanical switch or a relay contact switch is applied. The on / off switching operation of the switch 130 is controlled by a control unit (not shown). Since the switch 130 is connected in series with the second resistor 120, the current is supplied or cut off to the second resistor 120 according to the on / off switching operation.

The power control apparatus 100 of the present invention includes a third resistor R6 140 connected in parallel to the series connection of the second resistor 120 and the switch 130, Respectively, and a capacitor 160. The Zener diode 150 and the capacitor 160 are connected to each other. The Zener diode 150 has the same characteristics as the normal diode in the forward direction from the N bus line to the P bus line. The Zener diode 150 has a current flowing through the Zener diode 150, but no current flows in the reverse voltage (a very small leakage current flows) , The Zener breakdown occurs and the reverse bias flows and the current flows in the reverse direction. Therefore, in the drawing, a current lower in the N bus line direction from the P bus line can not flow in the reverse direction, but when the reverse bias occurs, the reverse current flows in the P bus line from the N bus line direction. The capacitor 160 serves to maintain a constant voltage.

The power supply control device 110 of the present invention is connected to the both output terminals of the Zener diode 150 and the capacitor 160 and receives a voltage across the control diode 150 to receive a low- And a DC / DC converter 170 for converting the converted signal into a sub-module. At this time, the voltage input to the DC / DC converter 170 changes according to the ON / OFF switching operation of the switch 130. [

Meanwhile, in another embodiment of the present invention, the power supply control apparatus 100 may include a current detector 180 for detecting a current flowing to the zener diode 150. The current detector 180 can detect current in various forms. For example, current may be detected using a current sensor as in the figure, or by using a voltage across a resistor (not shown) connected in series with the Zener diode 150. The current value detected by the current detector 180 is input to a controller (not shown). Then, the controller controls on / off switching of the switch 130 using the received current value so as to adjust the magnitude of the current flowing in the Zener diode 150. Throughout the present invention, the ON state of the switch 130 means that the line is short-circuited to conduct the current, and the OFF state means that the line is opened to block the current flow .

4 is a schematic diagram of a current flow for explaining a power supply control process of a submodule in a power supply control device for a submodule of an MMC converter according to an embodiment of the present invention.

4A shows the current flow in the low voltage section when the switch 130 is off and FIG. 4B shows the current flow in the high voltage section when the switch 130 is on Lt; / RTI > The power supply control device 100 for a submodule of the MMC converter according to the present embodiment adjusts the magnitude of the current flowing to the Zener diode 150 according to the on / off switching operation of the switch 130, Thereby reducing the burden on the user 150. The high voltage across the P-N bus line of the MMC converter applied to the present embodiment increases or decreases from 0 V to a predetermined maximum voltage Vmax. For convenience of description, the maximum voltage Vmax will be described as an example at 3 kV. Accordingly, in this embodiment, the power supply control device 100 receives an input voltage from a high voltage between the PN bus lines of the MMC converter, for example, 0 V to 3 kV, converts the input voltage into a low voltage of 300 to 400 V required for the submodule, .

4 (a), the power supply control apparatus 100 according to the present invention initially turns off the switch 130 to open the line, thereby causing current to flow through the second resistor 120 The input voltage between the PN bus lines is continuously increased from 0 to 1500 V (referred to as a first voltage). In this section (low voltage section), since the switch 130 is off, current does not flow through the second resistor 120, so that the loss generated in the second resistor 120 can be reduced. Therefore, the supply current I ₁₀ supplied through the first resistor 110 is divided into I ₁₁ and I ₁₄ . In this embodiment, the third resistor 140 is much larger than the second resistor 120. Thus, the supply current I ₁₀ is mostly I ₁₁ , which is again divided into I ₁₂ and I ₁₃ . The input voltage does not burden the zener diode 150 because the magnitude of the I ₁₂ current is not large in the low voltage interval of 0 to 1500V. Here, the first voltage of 1500V can be arbitrarily set and changed, and in the present embodiment, it is set by the magnitude of the _I12 current so as not to burden the Zener diode 150. [ If the input voltage is increased to 1500V or more, I ₁₀ is increased and I ₁₂ is increased, so that the Zener diode 150 is burdened.

In order to prevent this, as shown in FIG. 4 (b), after the input voltage between the PN bus lines reaches 1500 V, the switch 130 is turned on so that the current flows to the second resistor 120. Accordingly, the switch 130 is turned on in the section where the input voltage between the PN bus lines is 1500 to 3000 V (high voltage section), so that the line is short-circuited so that current flows through the second resistor 120, idle current I ₁₀ which is supplied as 110) is divided into _{I 11, I 14, I 15} . Since the third resistor 140 is much larger than the second resistor 120, the supply current I ₁₀ is mostly I ₁₁ and I ₁₅ , and I ₁₁ is again divided into I ₁₂ and I ₁₃ . Thus, the high voltage period is 1.5 ~ 3㎸ input voltage of the PN bus supply current I ₁₀ of the second resistor 120 in the portion (I ₁₅₎ is divided so reduce the size of the current I ₁₂ which is supplied to the Zener diode 150, So that the Zener diode 150 is not burdened.

As described above, in the embodiment of the present invention, while the input voltage between the PN bus lines increases from 0 to 3 kV (maximum voltage Vmax), 1.5 kV, which is a threshold voltage imposing load on the zener diode 150 The switch 130 is turned off so that the current I ₁₅ does not flow to the second resistor 120 and the switch 130 is turned on after the input voltage reaches _1.5 kV so that the current I ₁₅ flows through the second resistor 120. Accordingly, even when the switch 130 is turned off during the low voltage period in which the input voltage is in the range of 0 to 1.5 kV, the magnitude of the supply current I ₁₀ is small, so that the I ₁₂ is small so that the Zener diode 150 is not burdened. Since the supply current I ₀ is relatively larger than the low voltage period in the high voltage period of 1.5 to 3 kV, the switch 130 is turned on so that the supply current I ₁₀ flows to the second resistor 120 through the part I ₁₅ So that the magnitude of the current I ₁₂ flowing to the Zener diode 150 is reduced so that the Zener diode 150 is not burdened. That is, while I ₁₅ continues to increase from _1.5 kV to 3 kV, the magnitude of I ₁₅ increases so that I ₁₂ does not exceed a certain magnitude.

Thereafter, the switch 130 is maintained in the ON state while the first voltage is reduced to 1.5 kV at 3 kV, which is the maximum voltage Vmax, so that the supply current I ₁₀ is supplied to the second resistor 120 FIG part (I ₁₅₎ to flow when divided by so reducing the size of the current flowing through the Zener diode 150 and to reduce the burden on the Zener diode 150, the input voltage is equal to or less than the input voltage is below the first voltage 1.5㎸ The switch 130 is turned off to cut off the current flowing to the second resistor 120 so as to reduce the loss in the second resistor 120 and keep I ₁₁ constant. The first voltage becomes a threshold voltage that imposes a load on the Zener diode 150 while the input voltage increases or decreases from 0 to 3 kV. Accordingly, by turning on / off the switch 130 based on the first voltage, the loss occurring in the second resistor 120 can be reduced and the burden on the Zener diode 150 can be minimized.

If the power supply control apparatus 100 further includes the current detection unit 180, the control unit may initially turn off the switch 130 so that the voltage between the PN bus lines changes from 0 V to the maximum voltage The current I ₁₂ flowing to the Zener diode 150 is detected by the current detector 180 while the current I ₁₂ is increased to Vmax and the switch 130 is alternately turned on and off according to the magnitude of the detected current I ₁₂ (on / off) so as to repeat the supply / cutoff of the current to the second resistor 120. Specifically, the duty ratio of on / off switching of the switch 130 is varied so that the current I ₁₂ flowing to the Zener diode 150 is kept below a preset reference value. This is because the current I ₁₂ flowing to the zener diode 150 repeats supplying / blocking the current I ₁₅ to the second resistor 120 by appropriately adjusting the on / off duty ratio of the switch 130 in the control unit. So that it can adjust the amount of the liquid. Since the magnitude of the current I ₁₂ flowing to the Zener diode 150 is actually measured and the on / off switching operation of the switch 150 is performed according to the measured magnitude of the current I ₁₂ The amount of current I ₁₂ flowing to the Zener diode 150 can be better controlled than performing the on / off switching operation of the switch 150 on the basis of the first voltage, The burden on the Zener diode 150 can be reduced.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. Furthermore, the terms "comprises", "comprising", or "having" described above mean that a component can be implanted unless otherwise specifically stated, But should be construed as including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

110: first resistor 120: second resistor
130: Switch 140: Third resistance
150: Zener diode 160: Capacitor
170: DC / DC converter 180:

Claims (8)

At least one first resistor (110) connected between the PN busbars of the MMC converter;
A second resistor (120) serially connected to the first resistor (110);
A switch 130 connected in series to the second resistor 120;
A third resistor (140) connected in parallel to the series connection of the second resistor (120) and the switch (130);
A zener diode 150 connected in parallel to the third resistor 140; And
And a DC / DC converter (160) connected to both ends of the Zener diode (150) for converting a voltage between both ends of the Zener diode (150)
And controls the magnitude of the current flowing to the Zener diode (150) in accordance with on / off switching of the switch (150). The method according to claim 1,
Wherein the resistance of the third resistor (140) is greater than the resistance of the second resistor (120). The method according to claim 1,
Wherein the voltage between the PN bus lines increases or decreases in the range of 0 to a predetermined maximum voltage Vmax. The method of claim 3,
Wherein the switch (130) is turned off to prevent current from flowing to the second resistor (120) when the voltage between the PN bus lines is 0V and the first voltage is a low voltage period. 5. The method of claim 4,
The submodule of the MMC converter which turns on the switch 130 to allow the current to flow in the second resistor 120 during a high voltage interval in which the voltage between the PN bus lines is the maximum voltage Vmax from the first voltage, Power control device. The method according to claim 4 or 5,
Wherein the first voltage is determined according to a magnitude of a current flowing to the Zener diode (150). The method according to claim 1,
The method of claim 1, further comprising: detecting a magnitude of a current flowing through the Zener diode (150). The method of claim 1, further comprising: And the switch 130 is alternately turned on / off according to a current value of the Zener diode 150 detected by the current detector 180 to increase the voltage Vmax, 120) of the power supply for the sub-module of the MMC converter. 8. The method of claim 7,
Wherein the duty ratio of on / off switching of the switch (130) is varied to maintain the current flowing to the Zener diode below a preset reference value.

Images