KR101553765B1 - Method and system for preventing commutation failure in high-voltage direct current system - Google Patents

Abstract

The present invention relates to a system for preventing a current failure in a high-voltage direct current (HVDC) system, comprising: a rectifier composed of a plurality of thyristors and converting an AC input to the plurality of thyristors into a direct current; And a rectifier for rectifying the maximum value of the forced retard signal for forcibly delaying the current when the current controller and the DC line accident occurs, And a controller for controlling the input of the starter angle controller and the current controller such that the minimum value of the starter signal is input to the throttle valve as a point angle signal of the thyristor valve, So as to follow the output of the current controller.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and a system for preventing current failure in an HVDC system,

The present invention relates to a high-voltage direct current (HVDC) system using a thyristor-based rectifier and an inverter.

The power conversion in the HVDC system operates on sequential switching of thyristors. At this time, finite time is required for operation of the thyristor, and if this time is prolonged, current failure occurs.

In particular, current failures occur frequently due to the small operating angle at the inverter side [1,2] . Such a current failure causes the destabilization of the HVDC system, such as the burnout of the thyristor due to the overcurrent, the correction of the protection relay, and the variation of the transmission power [3-9] .

In addition to the leakage reactance and operating angle of the transformer, which are determined at the design stage, various causes of the current failure may be caused by the reduction of the AC voltage and the increase of the DC current [10-12] . In order to limit the increase of the DC current, a method of increasing the smoothing reactor or increasing the inverter side SCR to minimize the voltage decrease due to AC failure [13] , CCC-HVDC which adds a capacitor between the inverter side transformer and thyristor [14-16] . However, this is something to consider at the time of design and is not suitable for preventing current failure that may occur during HVDC operation.

In particular, the CCC-HVDC method can cause the thyristor to be burned out and shorten the lifetime due to excessive voltage stress, so studies are needed to solve this problem [17] . In addition to these methods, the following methods have been proposed to prevent current failure.

The first is VDCOL, a way to limit DC current. In order to prevent the overcurrent, DC current or DC voltage command value is lowered according to the DC voltage or AC voltage state. This is the most widely used method [18-22] . However, the design of VDCOL should reflect the strength of AC system [23] , but it does not reflect current change.

The second is to increase the Soho angle in case of current failure [24] . This method has difficulties in preventing current failures that may occur during recovery after AC voltage reduction due to failure as a measure for current failures.

In addition, the sensitivity analysis for the cause of the current failure has been studied, but the limitation is not reflected in the dynamic characteristics of the HVDC system. Therefore, further study is needed to reflect the dynamic characteristics of HVDC system to prevent current failure.

The present invention aims to provide a technique for minimizing the current failure prevention of the HVDC system by causing the output of the Soho angle controller to follow the output of the current controller at the inverter stage composed of a plurality of thyristors.

According to one aspect of the present invention, there is provided a system for preventing current failure in a high-voltage direct current (HVDC) system, comprising: a rectifier configured to include a plurality of thyristors, and a rectifier for converting the direct current converted from the rectifier into an alternating current, wherein the rectifier has a maximum value of a forced delay signal (Forced Retard Signal) for forcibly delaying the current when the current controller and the DC line accident occur, The throttle control apparatus according to any one of claims 1 to 3, wherein the throttle valve is controlled by a throttle valve control signal. And the output of the SOHO angle controller follows the output of the current controller.

According to another aspect of the present invention, there is provided a method for preventing current failure in a high-voltage direct current (HVDC) system, the method comprising: measuring an output phase voltage and a DC current, Calculating a difference between a maximum phase voltage and a maximum phase voltage by performing a difference operation on a voltage corresponding to a maximum value and a minimum value of each phase voltage when each phase voltage is decreased to be equal to or less than an AC system voltage, Calculating an overlap angle corresponding to a voltage drop of a leakage reactance due to an AC system voltage decrease and an increase in a DC current, calculating a phase shift between a minimum phase voltage and a minimum phase voltage, If it is operated below the current command value, it is checked whether or not each dot angle of the current controller and the SOHO angle controller intersects with each other. If crossed, the output of the SOHO angle controller And controlling the output of the current controller to follow the output of the current controller.

The present invention has the effect of improving the stability of operation of the HVDC system and minimizing current failure prevention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram schematically illustrating a configuration of a system for preventing current failure in an HVDC system according to an embodiment of the present invention; FIG.
FIG. 2 is a detailed block diagram illustrating a configuration of an inverter control unit in a system for preventing current failure in an HVDC system according to an embodiment of the present invention; FIG.
3 is a block diagram illustrating a controller configuration of an inverter side in a system for preventing current failure in an HVDC system according to an embodiment of the present invention.
4 is an overall flow diagram of a method for preventing current failure in an HVDC system in accordance with an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be appreciated that those skilled in the art will readily observe that certain changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. To those of ordinary skill in the art.

The present invention relates to a HVDC (High-Voltage Direct Current) system using a thyristor-based rectifier and an inverter, and more particularly to a high-voltage direct current (HVDC) system using a thyristor-based rectifier and an inverter for preventing commutation failure of the plurality of thyristors at an inverter stage comprising a plurality of thyristors The current of the AC line, the current of the DC line, the current loop of the current controller, and the point angle detected by the small angle controller are monitored in real time. If the current of the DC line is operated below the preset current command value, An intelligent controller, an optimal controller, a controller, and a controller, which compares the difference between the respective outputs of the current controller and the Soo angle controller with 0 according to whether or not each of the dots is crossed, , Robust controller, and outputs the result to the controller So that the output of the SOHO controller follows the output of the current controller, thereby improving the stability of the HVDC system and minimizing current failure prevention.

Hereinafter, a configuration of a system for preventing a current failure in an HVDC system according to an embodiment of the present invention will be described in detail with reference to FIG. 1 to FIG.

1 is a block diagram schematically illustrating a configuration of a system for preventing current failure in an HVDC system according to an embodiment of the present invention.

1, an HVDC system according to an embodiment of the present invention includes a rectifier 110 and an inverter 112. The HVDC system includes an A / D converter for converting an analog signal into a digital signal, (Not shown) including a DSP having an algorithm, a digital input / output circuit for generating a signal to the valve, and the like, and HVDC software configured by the controller of the rectifier 110 and the controller of the inverter 112 are mounted .

The rectifier 110 is composed of a plurality of thyristors 111, and converts the alternating current input to the plurality of thyristors 111 into a direct current.

At this time, the rectifier 110 includes a rectifier controller which is controlled such that a maximum value of the current controller and a forced delay signal (Forced Retard Signal) for forcibly delaying the current when the DC line accident occurs is input to the throttle valve signal of the thyristor valve do.

The inverter 112 converts a direct current converted from the rectifier 110 into an alternating current by a plurality of thyristors 113. The minimum value of the ignition signals corresponding to the small- The output of the SOHO controller follows the output of the current controller when the output of the SOHO controller is larger than the output of the current controller through the inverter control unit.

Referring to FIG. 2, FIG. 2 is a detailed block diagram illustrating a configuration of an inverter control unit in a system for preventing current failure in an HVDC system according to an embodiment of the present invention. Referring to FIG. 2, An inverter control unit 200 according to an exemplary embodiment of the present invention includes a phase voltage detection unit 210, a DC line current detection unit 212, a monitoring unit 214, a phase voltage calculation unit 216, an overlap angle calculation unit, And a dot blur processing unit 220.

In addition, although not shown in FIG. 2, in the HVDC system, the inverter controller includes a current controller for the error of the current, a voltage controller for the voltage error, a voltage controller for synchronizing the ignition signal of the voltage controller and the current controller with the grid voltage A comparator for comparing the output signal of the current controller or the voltage controller with the signal of the voltage controlled oscillator, a comparator for comparing the output of the current controller or the voltage controller with the output of the voltage controlled oscillator, And a maximum / minimum (Max / Min) selector for selecting a signal that meets the control condition from among the command values for the voltage error.

,

,

) 및 DC 선로 전류(

)를 측정하여 측정된 상 전압(

,

,

) 및 전류 값(

)이 기설정된 값 이하로 감소되는지 여부를 체크한다.The monitoring unit 214 monitors the phase of the output phase voltage output from the phase voltage detection unit 210 and the DC line current detection unit 212

,

,

) And DC line current (

) And the measured phase voltage (

,

,

) And the current value (

) Is reduced to a predetermined value or less.

,

,

) 이 최소한의 소호각 유지를 위한 AC 계통의 전압(

) 이하로 감소 되는지 여부를 확인한다.More specifically, the normal operating point of the HVDC system according to the present invention is determined by the current control of the rectifier 110, the minimum firing angle control, the current control and the so-called angle control of the inverter 112, Due to the excessive reduction of the current, the rectifier 110 may operate as the minimum firing angle controller and the inverter 112 as the current controller. However, when the controller is operated so that the DC line current is controlled by both the rectifier 110 and the inverter 112 before the operating point is determined, the DC line current can be very rapidly changed even with a small fluctuation of the AC voltage. That is, the decrease / increase of the DC current frequently occurs due to the change of the current voltage due to the AC failure. This phenomenon increases the incidence of current failures, so that each phase voltage monitored through the monitoring unit 214

,

,

) Is the voltage of the AC system for maintaining the minimum arc angle (

) Or less.

,

,

)이 기설정된 AC 계통 전압 이하로 감소된 경우 상기 각 상 전압 (

,

,

) 중 최대값과 최소값에 해당하는 전압에 대한 차이를 계산하고, 이를 통해 최대 상 전압과 최소 상 전압 간의 위상변이를 하기의 수학식 1을 통해 산출한다.As a result of the monitoring by the monitoring unit 214, the phase voltage calculator 216 calculates phase voltages

,

,

) Is less than or equal to the predetermined AC system voltage,

,

,

), The phase difference between the maximum phase voltage and the minimum phase voltage is calculated by the following equation (1): " (1) "

That is, in the HVDC system according to the present invention, since the thyristor is connected in the reverse direction in the inverter 112, the thyristor having the smallest phase voltage can be turned on. The voltage with respect to the three phases can be expressed by the following equation (2) in order to calculate the phase change at the moment when the three-phase voltage crosses as in the configuration of the thyristor 113 on the inverter 112 side.

At this time, thyristors are sequentially operated by crossing each of the three phases at a minimum value every 120 degrees, but if the voltage of the three phases is unbalanced, the phase shift occurs when the three phases are crossed.

This phase shift can be calculated from the part where each phase intersects with each other, and the voltage of a phase and b phase crosses from 0 ° to 180 °. When the voltage of a phase decreases due to failure, (3) " (3) "

The overlap angle calculation unit 218 calculates an overlap angle corresponding to the voltage drop of the leakage reactance due to AC system voltage reduction and DC current increase.

When there is no change in the DC line current, the voltage drop due to the leakage reactance is the same, so that the overlap angle increases due to the decrease in the a-phase voltage. As a result, the angle of incidence decreases and the rate of occurrence of current failure increases.

)는 하기의 수학식 4와 같이 나타낼 수 있다.Calculation of the value at which the SOH angle is reduced at the time of voltage reduction is possible from the calculation of the voltage drop due to the leakage reactance. Through the above equation (2), the current voltage (

) Can be expressed by the following equation (4).

In addition, the pole voltage of the converter connected to the a-phase and the b-phase is made equal by the Kirchhoff's law, and the voltage drop due to the leakage reactance is obtained from the pole voltage.

From the equation (5), the overlap angle can be obtained as shown in equation (6).

As the DC current increases, the voltage drop due to the leakage reactance increases, so that the overlap angle increases. As a result, the angle of incline decreases and the rate of current failure increases. The voltage drop due to the leakage reactance according to the DC current change can be obtained by the following equation (7).

When the current of the DC line is operated to be equal to or less than a preset current command value, the firing angle processor 220 checks whether the angle of each of the current controller and the small angle controller crosses each other. So as to follow the output of the current controller.

)이 상기 전류 제어기 출력 추종 시 필요한 소호각 필요량(

), 상기 상 전압 산출부(216)로부터 산출된 위상변이량, 상기 오버랩 앵글 계산부(218)로부터 산출된 오버랩 앵글의 증가량(

)을 모두 합하여 소호각 보정치(

)로 설정한다.Here, the blind processing unit 220 receives the output of the SOHO angle controller (

) Of the current controller output required to follow the current controller output

), The phase shift amount calculated from the phase voltage calculation unit 216, the increment amount of the overlap angle calculated from the overlap angle calculation unit 218

) Are summed to calculate the small correction value (

).

Also, the blind processing unit 220 inputs the result of comparing the difference between the outputs of the current controller and the SoHo controller to 0 and the error of each output to the controllers of various types described above, and then outputs the result And controls so that the output of the SOHO angle controller follows the output of the current controller.

3 is a block diagram showing a configuration of an inverter side in a system for preventing current failure in an HVDC system according to an embodiment of the present invention.

), 전류 제어기의 출력(

)이 각각 비교기(30), 오차 출력기(31)로 각각 분기되어 입력되고, 상기 오차 출력기(31)의 오차를 전술한 다양한 형태의 제어기(32)를 통한 결과, 상기 비교기(30)의 결과를 각각 33에서 스위칭하여 상기 소호각 제어기의 출력(

)이 전류 제어기의 출력(

)을 추종하도록 제어된다.
Referring to the dotted line area in FIG. 3, the present invention is characterized in that the inverter-side SOHO angle controller follows the output of the current controller by using the above-described various types of controllers at the portion where the decrease of the SOHO angle due to the voltage decrease and the overlap angle increase, Has been added, and the output of the soho angle controller (

), The output of the current controller

Are input to the comparator 30 and the error output unit 31 respectively and the error of the error output unit 31 is obtained through the controller 32 of the various types described above and the result of the comparator 30 And outputs the output of the SOHO angle controller (

) The output of this current controller

).

The configuration of the system for preventing current failure of the HVDC system according to an embodiment of the present invention has been described.

Hereinafter, a method for preventing current failure in the HVDC system according to an embodiment of the present invention will be described in detail with reference to FIG.

4 is an overall flowchart of a method for preventing current failure in an HVDC system according to an embodiment of the present invention.

4, first, the output phase voltage and the DC line current are measured in step 410. In step 412, it is determined whether the measured phase voltage and current value are decreased to less than the AC system voltage corresponding to the minimum angle of the predetermined thyristor .

As a result of the check, if the phase voltage is decreased to be equal to or less than the AC system voltage, the process moves to step 414 to calculate a difference between the maximum value and the minimum value of the phase voltages.

In step 416, the phase shift between the maximum phase voltage and the minimum phase voltage is calculated through the calculation of step 414.

In step 418, an overlap angle corresponding to the voltage drop of the leakage reactance due to the AC system voltage decrease and the DC current increase is calculated. In step 420, whether or not the current of the DC line is less than or equal to a preset current command value If the current command value is equal to or less than the preset current command value, the process proceeds to step 422, and it is checked whether the current controller and the SOHO angle controller cross each other.

As a result of the checking, if it crosses, the process proceeds to step 424, and a result obtained by comparing the outputs of the current controller and the SoHo controller with 0 and an error with respect to each output are input to the controllers of various types described above, And controls so that the output of the SOHO angle controller follows the output of the current controller.

As described above, the operation of the system for preventing the current failure of the HVDC system according to the present invention and the method of providing the same can be performed. While the present invention has been described with reference to the exemplary embodiments, Without departing from the scope of the invention. Accordingly, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by equivalents of the claims and the claims.

210: phase voltage detecting unit 212: DC line current detecting unit
214: monitoring section 216: phase voltage calculating section
218: overlap angle calculation unit 220:

Claims (8)

A system for preventing current failure in a High-Voltage Direct Current (HVDC) system,
A rectifier which is composed of a plurality of thyristors and converts AC inputted into the plurality of thyristors into DC,
And an inverter for converting the direct current converted from the rectifier into an alternating current,
The rectifier includes:
A rectifier controller which is controlled such that a maximum value of the current controller and a forced delay signal for forcibly delaying the current in the event of a DC line accident is input to the throttle valve signal of the thyristor valve,
The inverter includes:
And the output of the SOHO controller follows the output of the current controller through an inverter control unit which is controlled so that the minimum value among the ignition signals corresponding to the SOHO angle controller and the current controller is input as the firing angle signal of the thyristor valve.
The inverter control unit includes:
A monitoring unit for measuring an output phase voltage and a DC line current to check whether a phase voltage and a current value are reduced to a predetermined value or less;
As a result of the checking by the monitoring unit, if the phase voltage is decreased to be equal to or less than the AC system voltage, the phase shift between the maximum phase voltage and the minimum phase voltage is calculated through a difference operation between the maximum value and the minimum value of the phase voltages A phase voltage calculation unit,
An overlap angle calculation unit for calculating an overlap angle corresponding to a voltage drop of leakage reactance due to AC system voltage reduction and DC current increase;
If the current of the DC line is operated below the preset current command value, it is checked whether the current point of the current controller and the Soo angle controller cross each other. If the DC line is crossed, the output of the Soo angle controller follows the output of the current controller And a control unit for controlling the current of the HVDC system. delete The apparatus according to claim 1,
Wherein the output of the SOHO angle controller adds all of the required SOHO angles required for following the current controller output, the phase shift calculated by the phase voltage calculator, and the increment amount of the overlap angle calculated from the overlap angle calculator, Wherein the system is configured to prevent current failure in the HVDC system. The apparatus according to claim 1,
The difference between the outputs of the current controller and the SoHo controller is compared with zero and the result of inputting the error of each output to the controller and then the result of output is switched so that the output of the SoHo controller follows the output of the current controller Wherein the control unit is configured to control the current of the HVDC system. 5. The apparatus of claim 4,
Wherein the controller includes a proportional, integral, and differential component controller, an intelligent controller, an optimal controller, and a robust controller. A method for preventing current failure in a High-Voltage Direct Current (HVDC) system,
Measuring an output phase voltage and a DC current and checking whether the measured phase voltage and the DC current value are reduced to a predetermined value or less;
As a result of the monitoring part check, if the phase voltage is decreased to less than the preset AC system voltage, the phase shift between the maximum phase voltage and the minimum phase voltage is calculated through the difference calculation between the maximum value and the minimum value of the phase voltages And,
Calculating an overlap angle corresponding to a voltage drop of leakage reactance due to AC system voltage reduction and DC current increase;
If the current of the DC line is operated below the preset current command value, check whether each dot angle of the current controller and the SOHO angle controller cross each other, and if so, control so that the output of the SOHO angle controller follows the output of the current controller The method of claim 1, further comprising: 7. The apparatus according to claim 6, wherein the output of the solenoid angle controller is an output follow-
And comparing the result of the comparison between the current controller and the Soo angle controller with a difference of 0, and inputting an error of each of the outputs to the controller, and then switching the result of the comparison to output the result. . 8. The apparatus of claim 7,
Wherein the controller includes a proportional, integral, and differential element controller, an intelligent controller, an optimal controller, and a robust controller.

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